Yellow nutsedge (Cyperus esculentus L.) interference with polyethylene-mulched bell pepper (Capsicum annuum L.)

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Yellow nutsedge (Cyperus esculentus L.) interference with polyethylene-mulched bell pepper (Capsicum annuum L.)
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Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
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    Abstract
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    Introduction
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    Chapter 1. Interference of yellow nutsedge with bell pepper as influenced by initial yellow nutsedge plant density
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    Chapter 2. Critical yellow nutsedge-free period for bell pepper fruit production and vegetative growth
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    Chapter 3. Distance between yellow nutsedge and bell pepper at which pepper growth and yield is reduced
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    Chapter 4. Effect of 1,3-D + chloropicrin and metam-na on yellow nutsedge tubers grown in a greenhouse at different growth stages
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    Chapter 5. Summary and conclusions
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    Appendix A. Spatial pattern of planted tubers in tuber population experiment
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    Appendix B. Fruit number data
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    Appendix C. Total Kjeldahl N analysis
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    Appendix D. Sample calculations
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    References
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    Biographical sketch
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Full Text










YELLOW NUTSEDGE (Cyperus esculentus L.) INTERFERENCE WITH
POLYETHYLENE-MULCHED BELL PEPPER (Capsicum annuum L.)












By

TIMOTHY NEAL MOTIS


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2002














ACKNOWLEDGMENTS

I thank Dr. James P. Gilreath for providing assistantship funds and timely

encouragement. I thank Dr. Salvadore J. Locascio, chairman of my supervisory

committee, for providing advice, encouragement to excel professionally, and insights that

enhanced the quality of this dissertation. I also thank Dr. William Stall for his assistance

in experimental design and Drs. Sartain and Saba for their instruction and role as

supervisory committee members.

I extend special thanks Michael R. Alligood for help in field preparation,

instruction in laboratory procedures, practical suggestions, and technical expertise. I am

also grateful to Scott Taylor and the entire crew at the Horticulture Unit for their help in

crop establishment and harvesting.

I thank my wife, Paige, and my parents for their support, patience, and

encouragement. Lastly, I thank God for all the resources I have been provided with to

fulfill the requirements for this Ph.D.















TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS ................................................ ii

ABSTRA CT ......................................... . ................. v

INTRODUCTION

W eed/Crop Competition ............................................ 1
Yellow Nutsedge Biology .......................................... 12
Nutsedge Interference With Vegetables ............................... 16
Methods of Nutsedge Control ...................................... 20

CHAPTERS

1 INTERFERENCE OF YELLOW NUTSEDGE WITH BELL PEPPER AS
INFLUENCED BY INITIAL YELLOW NUTSEDGE PLANT DENSITY ....... 30

Introduction ...................................... ............... 30
M materials and M ethods ............................................. 31
Results and Discussion ............................................ 37

2 CRITICAL YELLOW NUTSEDGE-FREE PERIOD FOR BELL PEPPER
FRUIT PRODUCTION AND VEGETATIVE GROWTH .................. 135

Introduction ....................................... ............. 135
M materials and M ethods .................................. .......... 136
Results and Discussion ................................ ........... 140


3 DISTANCE BETWEEN YELLOW NUTSEDGE AND BELL PEPPER
AT WHICH PEPPER GROWTH AND YIELD IS REDUCED ............... 186

Introduction .................................................... 186
Materials and Methods ............................................ 186
Results and Discussion ........................................... 191










4 EFFECT OF 1,3-D + CHLOROPICRIN AND METAM-NA ON YELLOW
NUTSEDGE TUBERS GROWN IN A GREENHOUSE AT DIFFERENT
GROWTH STAGES ................................................. 225

Introduction ................................... ................. 225
M materials and M ethods ................................ ............ 227
Results and Discussion ................................ ........... 229

5 SUMMARY AND CONCLUSIONS ................................... 236

APPENDICES

A SPATIAL PATTERN OF PLANTED TUBERS IN TUBER POPULATION
EXPERIMENT ................................................... 242

B FRUIT NUMBER DATA ............................................ 244

C TOTAL KJELDAHL N ANALYSIS ................................... 250

D SAMPLE CALCULATIONS ........................................ 251

REFERENCES ....................................................... 258

BIOGRAPHICAL SKETCH ............................................. 269














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

YELLOW NUTSEDGE (Cyperus esculentus L.) INTERFERENCE WITH
POLYETHYLENE-MULCHED BELL PEPPER (Capsicum annuum L.)

By

Timothy N. Motis

May 2002


Chairperson: Salvadore J. Locascio
Major Department: Horticultural Sciences

Bell pepper, an economically important vegetable crop in Florida, cannot be

grown successfully without controlling yellow nutsedge. Methyl bromide, the only

chemical used in polyethylene-mulched bell pepper production that effectively controls

nutsedges, is being phased out of production. Information, therefore, is needed for

developing alternative yellow nutsedge control measures. Objectives of this research

were to determine the number of nutsedge plants tolerated by bell pepper, the time period

when yellow nutsedge must be controlled, the distance between nutsedge and bell pepper

plants at which pepper yields are reduced, and the activity of 1,3-dichloropropene (1,3-D)

+ 35% chloropicrin (Pic) and metam-Na on tubers at varying stages of growth. In field

experiments, bell pepper and yellow nutsedge plants were grown on polyethylene-

mulched, drip-irrigated beds. Respective treatments in the density, critical period, and








distance experiments included initial nutsedge tuber densities (ranging from 10 to 120

tubers-m'2), duration of yellow nutsedge interference with pepper and nutsedge-free time

(0 to 13 weeks after pepper transplanting), and initial distance between nutsedge plants

and a pepper plant (7.6 to 30.5 cm). In the greenhouse experiment, 1,3-D + Pic or

metam-Na was applied to dry, imbibed, and sprouted nutsedge tubers. Bell pepper yield

losses of greater than 10% were predicted with interference of nutsedge plants from 5

tubers-m2. Nutsedge-free periods of 4 to 5 weeks or 1 Y to 6/ weeks after pepper

establishment were required in spring and fall, respectively, for not more than 10% loss

of marketable pepper fruits. All distances of planted tubers from a pepper plant of 7.6 to

30.5 cm resulted in greater than 10% reductions in pepper fruit yield. In the greenhouse

experiment, metam-Na and 1,3-D + Pic effectively controlled yellow nutsedge for 28

days. Tubers imbibed with water before planting were more susceptible to 1,3-D + Pic

than tubers planted without prior water imbibition. Near total suppression of nutsedge

tubers was needed for a longer period of time in fall than spring to obtain adequate pepper

yields. When nutsedge tubers were planted 5 or 10 cm apart, suppression of nutsedge

needed to extend to the edge of the 61 cm-wide planting beds. The efficacy of 1,3-D +

Pic and metam-Na against yellow nutsedge was enhanced by minimizing volatilization of

fumigant gasses, and the efficacy of 1,3-D + Pic enhanced when applied to water-imbibed

tubers. Polyethylene-mulched bell pepper exhibited a low tolerance of yellow nutsedge in

the plant bed, and acceptable fruit production required the absence of nutsedge from

early- through mid-season.














INTRODUCTION

Weed/Crop Competition

Definition and Description of Competition

Effects of undesirable plants on crop plants have been a concern throughout the

history of agriculture (Grace and Tilman, 1990). Practices such as pruning, manipulating

crop spacing, and weed control have been adapted to maximize the performance of crop

plants. Each of these practices changes the proximity and subsequent growth of plants

that invariably occur in association with neighbors (i.e., other plants and/or organisms).

The interaction among a plant and neighbors is called interference and is further defined

as the effect that the presence of a plant has on the growth or development of its

neighbors (Radosevich, 1988).

Interference can negatively or positively affect a plant. Negative effects of plant

associations include competition, amensalism, and parasitism (Burkholder, 1952).

Competition involves mutually adverse effects on each of two associated

organisms/plants (Connell, 1990), whereas amensalism and parasitism describe

interactions where one of two organisms is not harmed (i.e., a plant that can exude

allelopathic substances) or benefits, respectively, by association with the negatively

influenced neighbor. Positive effects can occur, for instance, if two species occur in

symbiosis with each other. Distinctions among types of interference are important






2

because it is possible to incorrectly attribute crop yield loss, for example, to competition

when, in fact, yield loss may be due to other types of interference such as allelopathy.

Connell (1990) further described competition as "apparent" or "real." Apparent

competition was subdivided into two types. The first type involves indirect interaction

via a shared enemy (Holt, 1977, 1984). In this interaction, a shared enemy may benefit

from an increase in one plant species and subsequently harm a plant of another species.

The second type is indirect interaction between two species via another species on the

same trophic level. An example of this was described by Volz (1977) where competition

between corn and yellow nutsedge was attributed to the positive effect of yellow nutsedge

on soil microbes that, in turn, reduced corn yields via denitrification. Real competition,

as described by Connell (1990), occurs as one organism causes direct harm to a

neighboring organism via physical contact and abrasion or as two or more organisms use

a shared resource such as water, nutrients, or light.

Aspects of Resource Competition in Agricultural Settings

Real (resource) vs. apparent competition is often difficult to prove in nature

because there are usually a large number of species interacting with each other for an

indefinite period of time. In an agricultural setting, however, the number of species

interacting in the field and the duration of that interaction are limited to a growing season.

Also, the amount of inputs such as water and fertilizer is controlled in agricultural

settings.

Two components of resource competition are the effect on and response to

resources (Goldberg, 1990). Effect on resources was described as the rate of change in

light, water, or nutrient availability in response to increased plant density or biomass. By






3

studying the effect that plant species grown at varying densities have on resource

availability, it is possible to compare the competitiveness of two species by ranking their

ability to reduce the amount of available resources. In making interpretations related to

resource depletion it is important to distinguish between uptake and nonuptake effects on

resources. Uptake effects include physiological activity rates of plants and the ability of

plant organs to allocate resources. Nonuptake effects include adding resources (i.e,

nutrients and water) and modifying the physical environment.

Resource availability was described as the rate of change in a component of plant

fitness (i.e., crop growth and/or yield) in response to increased resource availability

(Goldberg, 1990). Competitive plants are those that are able to tolerate low resource

availability by maximizing resource uptake, minimizing resource loss, and maximizing

efficiency of resource conversion to new growth. It should be noted, however, that

tolerance of low resources may not be evidenced by increased yield or growth rates but

may instead be manifested by increased survival through means such as dessication

tolerance and ability to store resources obtained during temporary periods of abundance.

It is also possible that a plant species may be able to tolerate low amounts of one resource

but may not grow well at low amounts of another resource.

Climatic conditions, in addition to resources, are also important in understanding

interactions among crop species (Radosevich and Holt, 1984). In contrast to resources

such as light, water, and nutrients, conditions are not consumed. They include factors

such as temperature and photoperiod. Conditions may, in fact, alter the ability of plants

to use or tolerate low resource quantities.






4

Factors that Modify Crop/Weed Interference

In studying crop/weed interference it is important to understand factors that

modify interference. These include space, density, and species proportion (Radosevich

and Holt, 1984). Space is a conceptual unit consisting of the composite of all resources

and interactions needed for plant growth. The concept of "space" allows for the study of

how two plants or plant species interact without the need to determine the cause of the

interaction. This is because both plants share the same "space," with all its resources; and

each plant is a biological indicator of the space utilization of its neighbor. A related

concept, spatial pattern, refers to arrangement of and distance between plants on a

horizontal plane. Spatial pattern in competition experiments should be defined or

controlled to explain or minimize variation within treatments.

Density is the number of individuals per unit of area (Radosevich and Holt, 1984).

With increased density, a density is reached where interference occurs among neighboring

plants. As density of one species (weed) increases, the performance of neighboring plants

of another species (crop) is typically decreased. With further increases in weed density,

resources become limited and/or intraspecific competition among weeds increases such

that interspecific competition against the crop is reduced until the rate of loss in crop

performance levels off. This relationship between density and performance is known as

the law of constant final yield.

Species proportion refers to the proportion or ratio of each plant species in a plant

stand when there are at least two species within a population of plants (Radosevich and

Holt, 1984). The proportion or ratio is also known as relative density. Relative density of






5

each species in a mixture of species may or may not be of interest in weed-crop

competition studies, but it is a factor that may influence weed-crop interaction.

Methods of Studying Competition

Weed scientists are interested in developing threshold levels needed for making

informed weed management decisions. It is not adequate to only determine if yields are

influenced by the presence or absence of weeds. Additional questions must be answered

such as "what is the weed density that causes minimum and maximum yield loss," "when

do weeds need to be controlled," and "what is the distance around a crop plant that weeds

should be controlled?".

To answer such questions, it is necessary to determine thresholds including the

critical density, biological threshold, critical period, and area of influence. The critical

density is the weed density that a crop can tolerate without exceeding an economically

acceptable level of yield loss. The biological threshold is the weed density above which

little or no further yield loss occurs. Although a weed density resulting in the biological

threshold may be less than that occurring in a typical field, this parameter is needed to

determine the critical period. The critical period is the time period during the growing

season when a crop must be kept free of weeds. It relates to when weeds must be

controlled. The area of influence is the area over which a weed competes with a target

plant.

Appropriate experimental designs to determine these threshold levels include the

additive, replacement series, critical period, and neighborhood designs. Choice of

experimental design depends on the objectives of the researcher.








Additive designs

An additive design is used to determine the critical density and biological

threshold. In an additive design the crop density is held constant while weed density is

varied (Cousens 1985; Cousens, 1991; Radosevich 1987; Zimdahl 1980). Because field

crop densities are typically constant with varying weed densities, the additive study

mimics actual grower conditions. Furthermore, the design allows for evaluation of the

effects of full-season weed competition with a crop grown under production practices

used by growers.

In designing an additive study, it is important to choose appropriate levels of weed

density (Cousens, 1991). Commonly, a geometric series of densities such as 1,2,4, 8,

16, and 32 weeds-m"2 is used. An arithmetic series such as 1, 3, 5, and 7 weeds'm"2 may

be used for low weed densities when yield response is expected to be linear. In either

case, the densities chosen should include those resulting in minimal and maximal yield

losses; and it is desirable to have the greatest concentration of points on the steepest part

of the curve.

With results from an additive study it is possible to plot, via regression analysis,

the effect of increasing weed density on crop yield loss. According to Cousens (1991),

hyperbolic models usually provide a better fit than quadratic, square root, or sigmoidal

models. Choice of a model should depend not only on the coefficient of determination

(r2) value but also on biological properties. For example, a quadratic equation may give a

high value for r2 but may force an unacceptable maximum on data that is asymptotic.

Once the data are fitted to a model, the resulting equation may be used to estimate, within

the constraints of the design, parameter values and yield loss at any density.








Replacement series design

Unlike an additive design, a substitutive approach known as the replacement

series design allows for the separation of total (crop + weed) density and proportion of the

crop and weed in plant stands. In the replacement series design, proportions of two

species (i.e., crop and weed) are varied while the total density remains constant (Cousens,

1991). As it is difficult to vary crop density in the field, most replacement series studies

are conducted in the greenhouse. Monocultural stands of each species are also included

as treatments (Radosevich, 1987). Although proportions are used in the design, the

purpose of the design is not to study the effect of proportion per se (Cousens, 1991;

Radosevich, 1987) but to determine which of two species is the stronger competitor and

to learn how the two species interact. In accomplishing these objectives, derived rather

than direct variables are used.

To determine which species is the most competitive, relative yields in mixtures

are used. Relative yield for each species at each proportion is calculated by dividing the

yield with each proportion by the mean monocultural yield (Roush et al., 1989). Relative

yield for each species may then be plotted against proportion. The equivalent yield ratio

is the proportion at which the resulting lines for relative yield intersect. From the

equivalent yield ratio it is possible to determine which species is the most competitive.

If, for example, the equivalent yield ratio was obtained with a weed:crop proportion of

25:75, the conclusion would be that one weed could produce as much yield as three crop

plants, indicating that the weed is more competitive than the crop.

Relative yield total may also be plotted against proportion by summing the

relative yield for each species at each proportion. Relative yield total is useful for






8

comparing the performance of two species in mixtures vs. that with monocultures. For

instance, if relative yield total does not change over proportions it may be concluded that

the yield produced by both species in mixtures is equal to that expected with each species

grown separately.

Relative yield and relative yield total can also be used to learn something about

how the weed and crop interact. Several outcomes are possible (Radosevich, 1987).

First, it may appear that the weed and crop are planted so far apart that they do not

interact; however, it is possible that, in fact, the weed and crop compete equally (i.e.,

equivalent weed:crop yield ratio of 50:50) with the contribution to total yield by each

species in direct proportion to its presence in the mixtures. Secondly, it may be that one

species is more aggressive than the other and contributes more than the other to the total

yield, indicating that competition is for a common resourcess. A third possible outcome

is mutual antagonism where both species contribute less than expected to the total yield

and combined yield of both species is less when grown in mixtures than when either

species is grown in pure stands. A fourth possibility is mutual benefit, where the yield

with species grown in mixture exceeds that with pure stands.

With a replacement series design incorporating density in addition to proportion it

is also possible to evaluate the relative effects of intra- and interspecific interference of

each species (Radosevich, 1987; Radosevich, 1988) using a variable called reciprocal

yield. A separate line is drawn for each species by plotting reciprocal yield against

density using a linear equation. The result is a set of more or less parallel lines. The

degree of separation between the lines shows the extent of intraspecific competition while






9

the slope of the lines shows the extent of interspecific competition. A flat or steeply

sloped line shows a weak and strong interspecific competitor, respectively.

A requirement for proper design of a replacement series experiment is a total

density that is sufficiently high to obtain constant final yield (Cousens, 1991). If a

replacement series study is conducted with a density less than that resulting in constant

final yield, then interpretation of proportion effects may be influenced by the total density

used. It is possible to conduct replacement series studies with multiple total densities to

obtain information on potential density effects.

Critical period studies

To determine the critical weed-free period necessary to produce acceptable crop

yields, a weed removal and plant back study is conducted (Oliver, 1988) within a single

experiment or as separate experiments. These experiments are conducted using multiple

or single weed densities. If using a single density, the density should be that which

results in the biological threshold obtained with an additive study. The critical period

may be underestimated if the weed density used is too low (i.e., below the biological

threshold).

In a weed removal experiment, naturally occurring or planted weeds at crop

planting are removed at predetermined times during the growing season. A season-long

weed-free (weeds never established) and weedy (weeds never removed) check should be

included in the design. After weeds are removed, the crop is kept free of weeds for the

remainder of the season. Results obtained with a weed removal experiment show how

long a weed, present at crop planting, may be allowed to compete with the crop before

yields are reduced.






10

In a weed plant back experiment, weeds are allowed to emerge with the crop or

weeds are planted at predetermined times during a growing season. To obtain a desired

density, natural populations are either thinned or weeds are planted at the chosen density.

As with the removal experiment, a weed-free (weeds never established) and season-long

competition (weeds established at the same time as the crop) check should be included in

the design. Once the weeds are established they are allowed to grow and compete with

the crop for the duration of the season. Results from plant back experiments show how

long a crop must be kept weed-free to obtain satisfactory yields.

Within each replication (four to six are preferred), data such as crop yield

obtained with each weed removal or planting treatment may be converted to percent of

that obtained with a weed-free treatment (Oliver, 1988). These data can then be plotted

as a function of weed plant back or removal time on one graph to determine the critical

weed-free period. For example, if weed removal study data show that weeds may be

allowed to compete for 3 weeks and weed plant back study data show that a crop must be

kept weed-free for 5 weeks, then the critical period is between 3 and 5 weeks. From the

graph, a critical period can be identified for any level of yield loss.

Neighborhood studies

A neighborhood design is useful when the nearness of a weed species to a target

crop plant is of primary interest (Oliver, 1988; Radosevich, 1987). The two main factors

influencing performance of the target plant are distance between the crop and weed and

density of the weed species. The primary objective of these studies is to determine the

distance from a crop plant at which weed control is necessary.






11

In a typical neighborhood study, individual weeds are spaced 2 to 3 m apart within

a crop row, far enough to prevent intraspecific competition among weeds (Oliver, 1988).

Crop plants placed on either side of the weed plants are harvested several times during the

season, and weeds are harvested. At each harvest date, crop plants growing within

several row segments (for example, 0 to 12.5, 12.5 to 25, and 25 to 50 cm from the crop

plant) on both sides of the weed are cut at the soil surface. At each distance, samples

collected from all sides of the weed are combined to represent circles with varying

diameters around each weed.

There are variations of the experiment described by Oliver (1988). Goldberg and

Wemrner (1983) described a study in which the crop species is evaluated over a range of

weed densities, and the crop species is grown alone or is surrounded by individuals of the

weed species. The spatial arrangement of crop and weed species can also be varied.

Several equations have been used to describe the performance of the crop plant as

influenced by proximity to the weed species. Mack and Harper (1977) expressed plant

mass of plants in sand dunes as a log-linear function of factors including mass and

distance of neighbors. Goldber and Wemrner (1983) estimated performance (i.e., growth

rate, survival, or reproductive output) of a crop plant as a function of the "amount of

neighbors" (i.e., density, biomass, or leaf area). A variation of their equation included a

distance factor to account for diminishing effects of increasingly distant neighbors.

Weiner (1982) constructed a model in which seed yield of annual plants was a function of

the number and species of individual neighbors within each of several concentric

neighborhoods.






12

Yellow Nutsedge (Cvperus esculentus L.) Biology

Distinguishing Characteristics

The two Cyperus species of major agricultural importance are purple (Cyperus

rotundus L.) and yellow (C. esculentus L.) nutsedge. Both are perennials and are

considered among the world's worst weeds (Holm et al., 1977). Yellow nutsedge is

found in all U.S. states, whereas purple nutsedge is most commonly found in the southern

U.S. (U.S. Dept. Agric. Res. Serv., 1970). The two species commonly occur in mixed

stands and are difficult to distinguish until flowers appear. In mixed stands, purple

nutsedge can be differentiated from yellow by a reddish- or purplish- brown

inflorescence, leaves with boat-shaped leaf tips, and scaly rhizomes producing tubers and

bulbs in chains (Wills, 1987). By comparison, yellow nutsedge has a yellowish-brown or

straw-colored inflorescence, leaves with long, tapered tips, and weak rhizomes that

usually terminate in bulbs or single tubers. Typically, yellow nutsedge thrives in low,

moist areas, and purple nutsedge is found on well-drained soils (Holm et al., 1977).

Origins and Taxonomy

Nutsedge species are widespread in tropical and temperate zones around the

globe. The ancient, edible chufa is of Mediterranean origin (de Vries, 1991). Yellow

nutsedge, coded as CYPES in the Weed Science Society of America Composite list of

weeds, is classified by taxonomists into the class Angiospermae, the subclass

Monocotyledonae, order Graminales, and the family Cyperaceae (sedge family) (Gleason,

1963). Gleason (1963) reported approximately 75 genera and over 4000 species within

the Cyperaceae family.






13

Kukenthal (1936) described eight botanical varieties of C esculentus, but only

four (esculentus, leptostachyus, macrostachyus, and hermanii) were subsequently

recognized by Schippers et al. (1995) after testing characteristics of material collected

from herbariums from each continent. These varieties were called "weedy" by de Vries

(1991) and were distinguished from the cultivated variety, sativus, referred to as "Chufa."

Both weedy nutsedge and Chufa are included in C. esculentus according to Linnaeus

(1753). De Vries (1991) concluded that the similarity and history of Chufa and weedy

yellow nutsedges did not provide a taxonomical basis for separating the two groups, but

proposed that Chufa be named as a cultivar of yellow nutsedge (Cyperus esculentus L.

cv. Chufa) with the following criteria: yellow or greyed orange tubers, RHS Color Chart

numbers 163-167; tubers 0.5 cm to 3 cm long, borne on short rhizomes; rarely flowering;

sensitive to frost; and shoots ascending.

Propagation and Life Cycle

Yellow nutsedge can produce large numbers of seed as shown by Hill et al. (1963)

who, in Massachusetts, reported 605 million seeds'ha'. Viability of yellow nutsedge seed

varies. Justice and Whitehead (1946), for example, found that the viability of mature

seed ranged from less than 5% to greater than 40%. Factors influencing seed viability

include temperature, light, and moisture. Adequate soil moisture was critical for seed

germination in experiments by Lapham and Drennan (1990). Although growers of

irrigated cotton in California believed seed to be the main means of yellow nutsedge

dissemination (Thullen and Keeley, 1979), propagation of yellow nutsedge by seed is not

considered of major importance in cultivated fields (Mulligan and Junkins, 1975; Stoller,






14

1975; Stoller and Sweet 1987) due to lack of seedling vigor and absence of ideal

conditions for germination.

The primary source of yellow nutsedge establishment is underground tubers.

Most (99%) of the tubers in a peat soil were located at a soil depth of less than 25 cm in a

report by Tumbelson and Kommedahl (1961). Mature tubers are tan to brown colored

and spherical in shape (Stoller et al., 1972). A basal and distal end may be discerned with

the basal more rounded than the distal end.

Tubers lie dormant in the soil until stimulated to sprout. In temperate climates,

soil warming is the primary sprouting stimulus (Stoller, 1981). In addition to

temperature, mechanical disturbance has an effect on tuber dormancy. Taylorson (1967)

observed that both mowing and disk harrow cultivation sharply increased sprouting of

yellow nutsedge tubers during a period when tuber sprouting in an undisturbed stand was

low. Disk harrow cultivation increased sprouting more than mowing.

Tuber germination was not influenced by tuber sizes ranging from 61 to 294

mg-tuber'; however, dry weight of seedlings collected 16 days after planting tubers 5.3

cm deep in paper cups in a greenhouse at 22 to 30C was correlated at P < 0.01 (r = 0.57)

with planted tuber dry weight in a study by Stoller et al. (1972). Thus, tuber germination

and size were not related but yellow nutsedge plant vigor was a function of tuber size.

Upon breaking of dormancy and subsequent germination, rhizome(s) emerge from

the distal end of yellow nutsedge tubers (Jansen, 1971). Nodes, internodes, and

cladophylls are clearly visible on rhizomes. Upon exposure of a rhizome to light and

diurnal temperature fluctuations at the soil surface, basal bulbs are formed (Stoller et al.,

1972) 1 to 2 cm from where the rhizome tip first encounters light. Roots form and radiate






15

horizontally from the rhizome in the area near the basal bulb. Basal bulbs contain

meristematic tissue for the formation of roots, secondary rhizomes, leaves, and the flower

stalk (Stoller and Sweet, 1987).

Several weeks after a primary shoot (rhizome tip) emerges, secondary rhizomes

are produced from the basal bulb (Stoller and Sweet, 1987). These rhizomes turn upward

and form new basal bulbs that, in turn, form additional shoots and rhizomes resulting in

rapid vegetative proliferation of shoots. This vegetative phase is favored by long days of

14 to 16 h (Jansen, 1971). New tubers may also be formed from secondary rhizomes 4 to

6 weeks after shoot emergence (Stoller and Sweet, 1987). Growth ofnutsedge shoots and

rhizomes remains active until the middle of August (Jansen, 1971). Then, as daylength

decreases to less than 14 h, reproductive processes of flowering and tuber formation are

initiated (Jansen, 1971; Williams, 1982).

Numerous tubers and shoots can result from the sprouting and growth of a single

tuber. Tumbelson and Kommedahl (1961) found that one yellow nutsedge tuber in the

field produced 602 plants'm2 and 2184 tubers'm2 in 16 weeks. In spring 1999 in Florida,

Locascio and Dickson (2000) observed an increase in nutsedge (mixture of yellow and

purple) density from 181 to 950 plants-m"2 between 11 May and 22 June. Multiple shoots

per tuber and the ability of a tuber to sprout more than once contribute to high nutsedge

plant densities. Tumbleson and Kommedahl (1961) reported that, in petri plates, each

tuber produced zero to seven shoots, with an average of two. Stoller et al. (1972) found

that 52.2% and 26.5% of tubers sprouted two and three times, respectively.

Control of tubers is difficult due to tuber dormancy resulting in variable sprouting

times. Thullen and Keeley (1975) found that, in 2 to 4 weeks, 75% to 80% of yellow






16

nutsedge tubers sprouted with 40% of these producing more than one shoot. Some of the

unsprouted 20% to 25% of the tubers sprouted the following month, and sprouting

continued until all tubers either sprouted or died. One tuber in their experiment sprouted

for the first time 64 weeks after the first planting. They observed a high degree of

variability in sprouting characteristics such as multiple sprouting, sprouting interval, and

sprout weight.

Nutsedge Interference With Vegetables

Yield Losses Due to Nutsedge Interference

Yellow and purple nutsedge infestations, when not controlled, have resulted in

significant crop yield losses. Bell pepper fruit yield losses of 73% (Morales-Payan et al.,

1998) and 32% (Morales-Payan et al., 1997) have been reported in greenhouse studies.

Significant yield losses for other vegetables have also been reported. Watermelon fruit

yields were reduced by up to 98% by yellow nutsedge (Buker In et al., 1998). William

and Warren (1975) reported field grown crop losses due to full-season purple nutsedge

competition as follows: garlic 89%; okra 62%; two carrot cultivars, 'Kuroda' and

'Nantes' 39% and 50%, respectively; green bean 41%; cucumber 43%; cabbage 35%; and

tomato 53%. Purple nutsedge densities of 75 plants-m2 reduced radish yields by 100%

(Santos et al., 1998).

Thresholds Determined

Critical nutsedge densities and densities resulting in the biological threshold have

been reported for several vegetable crops. In a greenhouse study by Morales-Payan et al.

(1997), the critical purple nutsedge density for 10% bell pepper fruit yield loss was

obtained with an initial density of 50 tubers-m2. In this study, pepper fruit yield loss






17

increased linearly to 32% as initial tuber density increased from 0 to 200 tubers-m2. In

another study, yield loss increased linearly to 73% with increased initial tuber density

from 0 to 300 tubers-m2 (Morales-Payan et al., 1998). The critical density for 10%

tomato fruit yield loss and the density resulting in the biological threshold was 12.5 and

50 planted tubers'm-2, respectively, in work by Morales-Payan (1999). Marketable

tomato fruit yield loss with 50 to 200 tubers-m"2 was 45% compared to 65% loss for

medium size fruit. The critical density for 10% watermelon fruit yield loss was obtained

with 25 and 37 planted yellow nutsedge tubers-m2 in spring and fall, respectively, as

reported by Buker HI et al. (1998).

The critical nutsedge-free period has been determined for several vegetable crops.

William and Warren (1975) reported a critical purple nutsedge free period for several

vegetable crops grown on irrigated sandy clay to clay soils in Brazil. This period was

between 3 and 13 weeks for garlic; 3 and 7 weeks for okra, cucumber, and 'Nantes'

carrot; 3 and 5 weeks for tomato and 'Kuroda' carrot, and at 4 weeks for cabbage and

green bean. Their results showed that the critical nutsedge-free period for most crops is

during the first third of the growing cycle before the reproductive stage of the crop

begins. Their results also showed that crops such as garlic that did not produce a

significant amount of leaf canopy required a longer nutsedge-free period than for more

competitive crops such as tomato.

A replacement series study of yellow nutsedge interference with greenhouse-

grown tomato by Santos et al. (1997) showed that yellow nutsedge competed more

strongly with itself than with tomato. The dry weight of one tomato shoot equaled the dry

weight of three yellow nutsedge plants, indicating that tomato was a stronger competitor






18

than yellow nutsedge. Yellow nutsedge, however, competed more strongly than purple

nutsedge with tomato.

Means of Nutsedge Interference

Nutsedge interferes with crops such as bell pepper via competition for resources

including light, nutrients, and water. Of these three resources, light is often the most

important for vegetables supplied with nutrients and water via fertigation. William and

Warren (1975) concluded that purple nutsedge competed for light in slow growing

vegetable crops such as garlic that did not produce a large leaf canopy. Research by

Ponce et al. (1996) showed that bell pepper was sensitive to shading by weeds. They

found that bell pepper height and yield reduction increased with earliness of black

nightshade (Solanum nigrum) emergence. Bell pepper fruit yield was reduced 93% with

black nightshade emerging simultaneously with the pepper crop.

Yellow nutsedge competition with field-grown tomato for nutrients was observed

by Morales-Payan (1999). In this work, N, P, and K accumulation in yellow nutsedge

shoots increased while N, P, and K content in tomato leaves decreased with nutsedge

density. The rate of nutrient sequestration with increased nutsedge density was more

rapid with initial weed densities between 25 and 50 than between 100 and 200 plants-m'2.

With 200 plants-m2, N, P, and K uptake by nutsedge shoots was 153, 103, and 159

kg'ha', respectively.

Nutsedge interference with crops has also been attributed to allelopathic

substances (Drost and Doll, 1978; Drost and Doll, 1980; Gilreath, 1981; Meena and

Varshney, 1998; Sanchez et al, 1973). Most of the work has been done with agronomic

crops. For instance, Drost and Doll (1980) reported that yellow nutsedge tuber extracts






19

reduced corn (Zea mays) and soybean (Glycine max) dry weight more than leaf extracts.

Sanchez et al. (1973) found that yellow nutsedge extracts were phenolic in nature.

Quayyum et al. (2000) reported that the major compounds extracted from purple nutsedge

leaves and tubers via ethyl acetate followed by gas chromatography-mas spectroscopy

were dicarboxylic, phenolic, and fatty acids. Gilreath (1981) found that leachates from

purple nutsedge plants and tubers reduced the growth of cucumber (Cucumis sativus L.),

lettuce (Lactuca sativa L.), and tomato plants. Similarly, Kawisi et al. (1995) found that

purple nutsedge tuber extracts reduced the growth of squash (Cucurbita pepo cv. Felix)

roots by 95% to 99%.

Nutsedge interaction with bell pepper was influenced by crop production practices

in a study by Morales-Payan et al. (1998). With 70 kg-ha' of N applied to greenhouse-

grown bell pepper, fruit yield loss was not influenced by initial purple nutsedge densities

of 0, 100,200, and 300 plants-m2. Increasing the N supply from 70 to 210 kg-ha"' did not

reduce yield losses due to purple nutsedge competition. Use of seed vs. transplants was

also shown to influence weed interference effects on tomato. A minimum of one weed

control operation (fields were infested with weeds other than nutsedge) was necessary to

prevent yield loss of transplanted 'Springset' tomatoes compared to two weed control

operations when tomatoes were seeded into the field (Weaver and Tan, 1983; Weaver and

Tan, 1987).

Production practices such as crop spacing and row arrangement (Batal and

Smittle, 1981; Everett and Subramanya, 1983; Locascio and Stall, 1982; Locascio and

Stall, 1994; Stofella and Bryan, 1988), fertilizer rate (Everett and Subramanya, 1983;

Hartz et al., 1993; Locascio and Stall, 1982; Locascio and Stall, 1994) and method of






20

application (Batal and Smittle, 1981; Csizinsky, 1994; Hartz and Hochmuth, 1996;

Locascio et al., 1981), mulching (Locascio and Currey, 1973), transplanting depth

(Vavrina et al., 1994), and water management (Batal and Smittle, 1981; Hartz and

Hochmuth, 1996) have been studied to provide information needed to optimize bell

pepper crop vigor and resulting fruit yield. Crop vigor, as influenced by these practices,

is related to crop competitiveness against weeds.

Methods of Nutsedge Control

Bell pepper is a major Florida vegetable crop with over 7,400 ha planted annually

between 1984 and 1999 (Witzig and Pugh, 2000). In 1998-1999, the value of bell

peppers ($243 million) produced in the state ranked second to tomato with 15.4 % of the

total value of Florida vegetables. Considering the importance of bell pepper and high

crop yield losses associated with nutsedge infestations, nutsedge control is imperative.

Since the 1970's, methyl bromide has been the primary means of nutsedge control

in vegetable fields due to its consistent control of soil pests under a wide range of

growing conditions, low cost, and ease of use (Bewick, 1989; Overman and Martin, 1978;

Williamson et al., 1955). Due to its alleged contribution to the depletion of the

stratospheric ozone layer, methyl bromide is being phased out of production in the United

States (Environmental Protection Agency, 1999; Watson et al., 1992). Therefore, it is

necessary to develop alternative control strategies. Methyl bromide alternatives discussed

below include chemical and biological control, cultural methods, and solarization. These

may be used alone or in combination as an integrated approach to weed management

(Walker and Buchanan, 1982).








Chemical Control

Most of the methyl bromide alternative research has been focused on chemical

alternatives. These alternatives include other fumigants, herbicides, and fumigant-

herbicide combinations. As there are few new products being released, most chemical

alternatives being studied are old products.

The leading methyl bromide alternative for polyethylene-mulched tomato

production is 1,3 dichloropropene (1,3-D) + chloropicrin (Pic) combined with pebulate

(Locascio et al., 1997). Chloropicrin is very effective against soil-borne diseases and

1,3-D is an effective nematicide. Applied in combination, 1,3-D and Pic provided soil

disease and nematode control but lacked activity against purple and yellow nutsedge

(Gilreath et al, 1994; Stall, 1994). Hence, it was necessary to also apply a herbicide,

pebulate. This combination improved nutsedge control compared to that with 1,3-D + Pic

alone (Gilreath et al., 1996) and has provided a similar degree of pest control as methyl

bromide (Gilreath et al., 1994; Locascio et al., 1997). Locascio et al. (1997) reported that

pebulate (at 4.5 kg-ha') combined with 1,3-D + 17% Pic (at 327 L-ha"') produced field-

grown tomato yields that were 85% to 100% of those obtained with methyl bromide.

There are several problems in using 1,3-D. The label requires that applicators

wear suits made of tyvek, a full face respirator, and rubber gloves and boots. This gear is

expensive and uncomfortable. Another problem is a three-week delay between

application and crop planting. Because of these disadvantages and others, work has been

done to investigate the efficacy of pebulate combinations that do not include 1,3-D.

Results have been inconsistent. In a study by Gilreath et al. (1995) control of purple

nutsedge with pebulate combined with Pic, dazomet, or metam-Na was equal to that






22

obtained with methyl bromide. Olson et al. (1996), on the other hand, found that metam-

Na plus pebulate did not reduce yellow and purple nutsedge infestations compared to

those found in untreated plots. In a study by Locascio et al. (1995), metam-Na plus

pebulate reduced nutsedge numbers below those present in untreated plots, but numbers

were not as low as with methyl bromide.

Due to problems with the use of in-row applied 1,3-D, work has also been

conducted with broadcast applications of 1,3-D + Pic. With broadcast applications,

bedding and mulch application can be done several days after the chemical is broadcast

applied by injection to about 25 cm, thereby precluding the need for protective clothing

for a large number of workers. Broadcast applications of pebulate combined with 1,3-D

+ 17% and 35% Pic rototilled to a 25 cm depth in a 1.8 m area, however, did not improve

nutsedge control relative to that obtained with in-row applications (Locascio and

Dickson, 2000).

For pepper production, there is no methyl bromide alternative that consistently

controls weeds. Pebulate has provided some nutsedge control when applied with soil

fumigants but is not registered for use on pepper. In one experiment, 3.4 kg-ha'" pebulate

reduced pepper plant vigor by 15% (Bagley and Beste, 1982). Stall and Gilreath (1996),

however, found that pepper was tolerant of up to 4.5 kg-ha' pebulate. Napropamide is

the only herbicide with nutsedge activity labeled for use on pepper, and control of

nutsedge with this material is erratic (Pritts and Kelly, 2001). In polyethylene-mulched

fields, napropamide must be applied preplant on the bed surface, and there is no post-

emergence herbicide that may be applied that controls nutsedge in pepper.






23

The phaseout of methyl bromide and the lack of herbicides with acceptable

nutsedge activity is likely to increase reliance on dazomet, 1,3-D + Pic, and metam-Na.

Dazomet and 1,3-D + Pic have shown little activity against nutsedge in tomato production

(Locascio et al., 1997). Mixed results have been obtained with metam-Na alone or in

combination with 1,3-D + Pic.. Csinos et al. (2000) showed that metam-Na (468 L-ha')

+ 1,3-D with 17 % Pic (126 L-ha7') provided good control of most pests when covered

with polyethylene film immediately after treatment. In contrast, Jaworski et al. (1980)

and Locascio et al. (1997) found that metam-Na was less effective than methyl bromide

in terms of nutsedge control in pepper transplant and tomato production fields,

respectively. Erratic performance of metam-Na may be due to fumigant loss by

volatilization (Goldwasser et al., 1994; Klefield et al., 1991) and variable temperatures at

time of application (Ben-Yephet and Frank, 1985), fumigant rates (Stall, 1994), and

differences in soil distribution of the chemical as influenced by soil texture (Ben-Yephet

and Frank, 1989; Gerstl et al., 1977).

Another potential strategy for nutsedge control in pepper is repeated stimulation

of tuber sprouting (i.e., by practices such as irrigation and tillage) and herbicide

applications to emerged nutsedge shoots prior to crop establishment. This strategy is

based on the observation that nutsedge carbohydrates are lost with multiple sproutings.

Stoller et al. (1972) reported that tubers germinating three successive times lost 60% of

their initial dry weight and content of carbohydrates, oil, starch, and protein during the

first germination. This approach has shown promise in work with glyphosate (Cools and

Locascio, 1977; Fraedrich et al., 2002), a broad-spectrum, systemic herbicide that is

readily translocated throughout a plant after foliar application and absorption (Doll and






24

Piedrahita, 1978; Chase and Appleby, 1979a; Pereira, and Crabtree, 1986). It has activity

against nutsedge (Cools and Locascio, 1977; Chase and Appleby, 1979b; Doll and

Piedrahita, 1982), especially when tubers are nondormant and when complete coverage of

actively growing, young shoots is obtained (Fraedrich et al., 2002; Zandstra and

Nishimoto, 1977; Doll and Piedrahita, 1978).

Cools and Locascio (1977) obtained better purple nutsedge control in the summer

and fall than during the spring, and excellent control (up to 98%) was obtained only with

applications made in two or three consecutive seasons. Tuber dormancy, due to low

temperatures, reduced the efficacy of glyphosate in the spring, but two spring-season

applications one week apart provided better control than one. Fraedrich et al. (2002)

applied glyphosate to fields infested with purple nutsedge up to three times in 1999 and

two additional times in 2000. Over this two year period, the number of viable tubers

declined by 98% from 516 to 11 tubers-m2. They found that soil moisture and nutsedge

plant size at application time influenced the efficacy of glyphosate. The influence of soil

moisture on glyphosate performance was also shown by Mosssavi and Dore (1979) who

found that glyphosate activity on purple nutsedge was reduced when applied to drought

stressed plants compared to that obtained when applied to plants grown with soil moisture

at field capacity.

Biological Control

Biological control of weeds is accomplished with natural enemies. Classical

biological control is the introduction ofnonindigenous natural enemies (Phatak et al,

1987) whereas inundative biological control is the timely augmentation of an indigenous

natural enemy resulting in high inoculum pressures and subsequent suppression or death






25

of the weed host (Phatak et al., 1987). Phatak et al. (1987) listed 132 insects that have

been associated with purple and/or yellow nutsedge. About half of these were known to

feed on crop plants, and four of the insects have been studied in detail. These include

three moths (Bactra verutana Zeller in the United States, B. minima Meyrick and B.

venosana Zeller in the Indian subcontinent) and a weevil (Athesapeuta cyperi Marshall in

southeast Asia). Attempts using the classical strategy to control purple nutsedge at

several locations, however, were unsuccessful as evidenced by lack of subsequent

recovery and/or high parasitism of the biological control agents. Using an inundative

approach, Frick and Chandler (1978) reduced aboveground growth of purple nutsedge by

30% to 60% within four to seven weeks after the last release of B. verutana.

A fungal bioherbicide agent, Dactylaria higginsii, was reported to be pathogenic

to greenhouse-grown purple and yellow nutsedge (Kadir and Charudattan, 2000).

Nutsedge shoot and tuber dry weights were reduced 73% and 67%, respectively, after

inoculation with conidial suspensions of D. higginsii. A rust organizm, Puccinia

canaliculata, applied alone or in combination with herbicide(s) has also been evaluated

(Beste et al., 1992; Callaway et al., 1986) for nutsedge control. Combination treatments

ofpebulate followed by rust inoculation, however, were not effective against yellow

nutsedge in tomato fields (Beste et al., 1992).

Research has also showed that yellow nutsedge is inhibited by allelopathic effects

of sweet potato (Ipomoea batatas). Harrison and Peterson (1994) found that yellow

nutsedge was highly sensitive to compounds in the periderm of sweet potato cv. Regal.

In an earlier experiment (Harrison and Peterson, 1991), they found that yellow nutsedge

did not greatly affect sweet potato growth, but yellow nutsedge shoot dry weights of






26

plants grown with sweet potato were less than 10% of those obtained in the absence of

sweet potato.

There are several reasons for inconsistent weed control with biological control

agents. First, control is generally achieved slowly and may not occur in time to prevent

the competitive effects of weeds. Secondly, establishment of the bioherbicide agent is

difficult to obtain if conditions needed for fungal growth do not exist during the crop

growing season. Finally, bioherbicide agent survival in the field may be reduced by

fungicides and insecticides applied to vegetable crops.

Cultural Methods

Cultural practices that may be manipulated to control weeds include cultivation,

crop rotation, use of cover crops, and mulching. Preplant tillage brings nutsedge tubers to

the surface where they are subject to dessication and/or cold injury (Stoller and Wax,

1973; Wax, 1975). Three cultivations at monthly intervals reduced the number of newly

formed yellow nutsedge tubers in the field (McCue and Sweet, 1982). Preplant tillage

can also be used in conjunction with herbicides or soil fumigants as cultivation has been

shown to stimulate tuber sprouting (McCue and Sweet, 1982), rendering them susceptible

to chemical control. A disadvantage of cultivation is that nutsedge tubers can be spread

by tillage equipment.

Crop rotation and use of cover crops was used for many years, prior to the time

when methyl bromide was widely used, to control weeds. Yellow and purple nutsedges

are sensitive to shading from crops that produce a canopy early in the season (Dawson,

1964; Keeley and Thullen, 1978; Khan and Mahmood, 1991; Morales-Payan et al., 1997;

Patterson, 1982; Walker and Buchanan, 1982). Therefore, choice of crops in a rotation,






27

as well as cover crops, should be made based on the ability of crops to produce a canopy

early in the season that shades out nutsedge. Although crop rotation incorporating cover

crops has been an important tool for weed management in the past, reliance on soil

fumigants and synthetic fertilizers coupled with reduced land area available for vegetable

production has reduced the use of crop rotation in recent years.

Flooding the soil prior to crop planting to control nutsedge has also been studied.

Nutsedge control, however, was poor because dormant tubers were able to sprout after the

flooding period had ended (Nelson et al., 1999). Problems with soil flooding include the

need for large quantities of water, mosquito control, and impact on neighboring crops.

Mulching with materials such as polyethylene controls weeds by excluding light.

This method, though, does not control nutsedge due to the ability of rhizome tips to

penetrate commonly used polyethylene films. (Locascio and Currey, 1973; William,

1976).

Solarization

Soil solarization is a practice used to control weeds and diseases with high

temperatures induced by covering planting beds, about eight weeks prior to crop planting,

with clear, polyethylene film. After solarization, the polyethylene must be painted to

exclude light, thereby limiting potential growth of dormant weed seeds. Painting of the

mulch (black in spring; white in fall) is also necessary to prevent crop injury during

periods of high soil temperatures.

Effectiveness of soil solarization is dependent on obtaining sufficiently high soil

temperature to control/kill weeds. Chase et al. (1999) obtained 100% nutsedge tuber

mortality using diurnal soil temperature oscillations with maximum temperatures of 50






28

and 56C and a minimum temperature of 26C. They also found that 6 weeks of

solarization with thermal-infrared-retentive (TIR) films resulted in higher temperatures

and a higher level of purple nutsedge control than with a 30-jtm low density polyethylene

(LDPE) clear film. Residual nutsedge control was 95% and 92% with 75- and 100-jtm

TIR film, respectively. Stevens et al. (1999), found that a TIR film increased the soil

temperature at 5 cm depth by 5C compared to that obtained with conventional LDPE

film.

Chase et al. (1999) also found that, with TIR films, more emerged purple nutsedge

plants were killed by foliar scorching than with the LDPE film. Foliar scorching under

clear films occurs due to the failure of nutsedge rhizome tips to penetrate the mulch

(Chase et al., 1998 and Patterson, 1998). Chase et al. (1998) attributed the lack of

rhizome tip penetration through clear mulch to a light-dependent morphological change in

rhizome tips causing the sharply pointed scale leaves surrounding the meristem to unfurl.

Foliar scorching is an important method of nutsedge control with solarization as it

is difficult to obtain temperatures lethal to tubers occurring below 10 to 12.5 cm

(Albregts et al., 1996; Chase et al., 1999).

Solarization alone or in combination with herbicides works best in hot, arid

climate such as that in Israel. In Florida, results have been mixed. In some instances,

solarization has been found to be effective for tomato (Overman, 1985; Overman and

Jones 1986) and strawberry (Overman et al., 1987). Gilreath et al. (1999) found that fall-

grown tomato yields with solarization were less than those obtained with methyl bromide.

In their study, solarization provided a degree of purple nutsedge control similar to that

with methyl bromide, but crabgrass [Digitaria ciliaris (Retz.) Koel.] and root knot






29

nematode (Meloidogyne spp.) control was less with solarization than methyl bromide.

Strawberry yields with solarization (21 Aug. to 9 Oct.) alone were much lower than yields

with methyl bromide-chloropicrin due to a low number of days with soil temperatures

>50 C (Locascio et al., 1999).

Inconsistent performance and lack of widespread grower acceptance of

solarization in Florida is due to several factors. Frequent cloud cover/rain and subsurface

irrigation result in reduced soil temperatures and effectiveness of solarization. Also, the

polyethylene film must be laid down about two months before planting. Therefore,

solarization is most feasible as a fall production practice in a state where most vegetables

are grown during the spring season.














CHAPTER 1
INTERFERENCE OF YELLOW NUTSEDGE WITH BELL PEPPER AS
INFLUENCED BY INITIAL YELLOW NUTSEDGE PLANT DENSITY

Introduction

Reduction of crop yields by weed interference is a function of weed density. An

additive design is suited for studying the effect of weed density on crop/weed interaction.

In an additive design, crop density is held constant while weed density is varied (Cousens

1985; Cousens, 1991; Radosevich 1987; Zimdahl 1980). Important parameters

determined with an additive design include the critical weed density and biological

threshold. The critical density is the weed density a crop can tolerate without exceeding

an economically acceptable level of yield loss. The biological threshold is the weed

density above which little or no further yield loss occurs.

The critical nutsedge density and biological threshold have been reported for

several vegetable crops. In a greenhouse study by Morales-Payan et al. (1997), the

critical purple nutsedge density for 10% bell pepper fruit yield loss was obtained with an

initial density of 50 nutsedge plants-m2. In their study, pepper fruit yield loss increased

linearly to 32% as initial nutsedge density increased from 0 to 200 plants-m2. Thus, the

nutsedge density resulting in the biological threshold was not reached. In a field study by

Morales-Payan (1999), yellow nutsedge interference by plants from less than 25

tubers-m"2 reduced marketable tomato fruit yield by 10%. In the same study, nutsedge

interference reduced marketable tomato fruit yield by approximately 45% with initial






31

nutsedge densities of 50 to 200 plants-m"2. The biological threshold for tomato yield loss,

then, was obtained with 50 nutsedge plants-m2.

Crop response to weed density may vary with production practices used. For

example, applied N rate and purple nutsedge tuber density interacted in their effects on

fruit yield of greenhouse-grown bell pepper (Morales-Payan et al., 1998). With 70 kg

N-ha', initial nutsedge plant density had no effect on bell pepper fruit yield. With 140

and 210 kg N-ha1, pepper yields declined linearly up to 73% with an increase in nutsedge

density from 0 to 300 plants-m2.

Field-grown bell pepper yield response to yellow nutsedge population has not

been described. This research was conducted to determine the effect of planted yellow

nutsedge tuber densities on growth and fruit yield of bell pepper planted at two in-row

spacings.

Materials and Methods

Design

Experiments were conducted during spring and fall on a Kanapaha fine sand

(loamy siliceous, hyperthermic, Grossarenic Paleaquult) in 1999 and on an Arredondo

fine sand (loamy, siliceous, hyperthermic, Grossarenic Paleudult) in 2000 at the

Horticultural Research Unit of the University of Florida in Gainesville, Fla.

Treatments were arranged as a factorial with two in-row pepper spacings (22.9

and 30.5 cm) and five to six planted tuber densities with five replications. In spring 1999,

0, 30, 60, 90, and 120 tubers-m2 were planted. In fall 1999, 0, 10,20, 30, 60, and 90

tubers-m2 were planted. In both seasons in 2000, 0, 15, 30,45, 60, and 90 tubers-m"2

were planted.








Establishment and Maintenance Procedures

Beds were formed on 1.2 m centers, fumigated with 392 kg-ha-' of 75:25 methyl

bromide:chloropicrin injected 20 cm deep with two shanks to kill existing tubers, and

covered with polyethylene mulch (Sonoco; 0.0038 cm thickness; black in spring; white in

fall). Planting holes were punched within one to two weeks after fumigation, but in fall

1999 they were punched five weeks after fumigation due to a delay in availability of

pepper transplants. Holes for pepper transplants were punched with a planting wheel to

form double rows of holes spaced 22.9 or 30.5 cm apart in the rows. Holes for nutsedge

tubers were punched via a board with dowels 7.6 cm long. For each season, the number

of dowels on the board corresponded to the highest tuber density used so that all plots

received the same number of holes.

Bell pepper ('X3R Camelot') seedling and nutsedge tuber planting began on the

day holes were punched (Table 1-1). Each nutsedge planting hole received one tuber in

plots treated with the highest tuber density. In remaining plots, the number of holes

planted varied according to tuber density. For example, in spring 2000, a maximum of

120 tubers-m2 was planted. To plant 60 tubers'm2, one of every two holes received a

tuber. Within each treatment, the same spatial pattern of planted tubers was used.

Drip irrigation with biwall tubing (orifice diameter, 0.025 cm; emitter spacing, 30

cm; flow rate of 1.89 L per 30.5 m per min) placed on the soil surface at the middle of

each bed simultaneously with polyethylene mulch application was used to supply water as

needed to prevent moisture stress to plants. Irrigation times for each week were

scheduled to apply approximately 75% of the mean daily volume of ET for the previous

seven days.






33

Plants received 224:37:186 kg ha-' ofN-P-K, respectively. All P and 40% ofN

and K were applied preplant-incorporated during bed formation. The remainder of N and

K was drip-applied in 10 equal weekly applications. Pesticides were applied as needed

for insect and disease control.

Measured and Derived Variables

Measured variables included pepper and nutsedge plant height, pepper leaf area,

dry weight of pepper [(leaves, stem, and fruit (if present)] and nutsedge (shoots) plants,

nutsedge shoot number, N concentration in pepper and nutsedge plants, and harvested

pepper fruit weight. Pepper leaf, stem, and fruit dry weights were summed to obtain total

dry weight per pepper plant. Using dry weight data from pepper plants grown weed-free,

percent losses of leaf, stem, fruit, and total dry weight were calculated.

Nitrogen concentration in pepper was determined for leaf, stem, and fruit tissue.

The N concentrations were determined for fruit on pepper plants sampled before harvest

and for harvested fruit. When no fruit was present, a value of zero was assigned for N

concentration and N accumulation. Accumulation of N by pepper leaf, stem, and fruit

tissue was the product of N concentration multiplied by dry weight. Dry weight of

harvested fruit was calculated multiplying the fresh weight of harvested fruit by percent

dry weight of a sample of harvested fruit. During each season, fruit N uptake for each

harvest was summed to obtain total fruit N uptake. In a similar manner as for dry weight

data, percent losses of leaf, stem, fruit, and total N uptake were also determined.

Nutsedge N uptake was derived the same as for pepper leaf and stem N uptake.

Methods for determining nutsedge dry weight per unit land area, however, differed in

1999 and 2000. In 1999, nutsedge shoot N uptake was derived by multiplying the dry






34

weight of a known number of sampled stems by the number of shoots in a unit area of

bed surface. In 2000, nutsedge shoot N uptake was derived using the dry weight of all

shoot biomass within the unit of land area.

Harvested pepper fruit weight data for each harvest were summed to obtain total

fruit weight for each fruit size category. Large fruit yield was derived from the sum of

U.S. Fancy and U.S. No. 1 fruit. Yields of U.S. Fancy, U.S. No. 1 and U.S. No. 2 fruit

were summed to obtain marketable fruit yield. Total yield was the sum of yield for all

fruit grades including culls. Harvested fruit yields were converted to percent loss, relative

to values obtained with pepper grown weed-free.

Data Collection Procedures

Pepper plant heights, the distance from the bed surface to the highest bud, were

measured during flowering, fruit development, and after final fruit harvest (Table 1-1)

from four representative plants in the middle of each plot. A stake, placed in the ground

at pepper flowering, was used to show the location of the four plants so that height data

were collected from the same plant each time.

Nutsedge shoot heights, the distance from the bed surface to the highest growing

point of leaf blades, were measured at the same times as pepper plant heights (Table 1-1)

from eight leaf blades in the middle of each plot.

Nutsedge shoots were counted in a 0.1 m2 area in each plot during pepper

flowering, fruit development, and after final fruit harvest (Table 1-1). In 1999, shoots

were counted in the middle of each plot where shoot heights were obtained. To avoid

compromising shoot height data, heights were obtained from leaf blades that appeared






35

undisturbed, or heights were measured before shoot counting. In 2000, shoots were

counted at one end of each plot in a 0.1 m2 area with nutsedge and pepper end-plants.

Nutsedge shoots were sampled in a 0.1 m2 area at one end of each plot the same

times as shoots were counted (Table 1-1). Shoots were sampled by cutting at ground

level. In 1999, a portion (14 to 28 shoots) of the shoots in the 0.1 m2 area was sampled.

In 2000, to improve the likelihood of obtaining a representative sample, all of the shoots

in the 0.1 m2 area were sampled. Each sample of shoots was placed in a labeled paper

bag and dried in a forced air drier at 60 C prior to recording dry weight. Subsequently,

samples were ground with a mill (Wiley) to a particle size of< 0.6 mm diameter prior to

determining total kjeldahl N (TKN) using a 100 mg sample. Tissue were digested in

H2SO4 and analyzed by Rapid Flow Colorimetry (Hanlon et al., 1996).

In each season, a representative pepper plant from each end of every plot was

sampled during pepper flowering, fruit development, and near the end of fruit harvesting

(Table 1-1). In plots with nutsedge, pepper plants surrounded by nutsedge were sampled.

Leaves, stem, and fruit(s) (if present) of each plant were separated and placed in bags

after passing leaves through an area meter (LI-3100; LI-COR; Lincoln, NE) to obtain total

leaf-plus-petiole area per pepper plant. Leaf, stem, and fruit tissue were dried at 60 C

prior to recording dry weight for leaf, stem, and fruit (if present) tissue. Dried tissue was

then analyzed for TKN in the same manner as above. Pepper leaf and stem tissue

sampled at pepper flowering were combined for TKN analysis. For plants sampled

during fruit development and after fruit havest, TKN was determined for leaf, stem, and

fruit (present only during fruit development) tissue.






36

In spring and fall 2000, light (photosynthetic photon flux density) readings were

taken via a radiometer-photometer (LI-250; LI-COR; Lincoln, Neb.) with a one meter

long quantum sensor (LI-191 SA; LI-COR; Lincoln Neb.) at pepper flowering and fruit

development. In each plot with nutsedge, a reading was taken one meter above the tallest

plants to determine the amount of light available to pepper and nutsedge plants. A second

reading was taken with the sensor placed flush with the top of the pepper plants with

nutsedge leaf blades laying over the bar. The second reading was divided by the first and

multiplied by 100 with the resulting percentage subtracted from 100.

Pepper fruits were harvested twice each season except for fall 1999 when fruits

were harvested once. After removing culls, fruit were graded as US fancy, US No. 1, and

US No. 2 fruit according to U.S. Dept. of Agriculture standards.

Data Analysis Procedures

Data were subjected to analysis of variance using SAS (SAS, 2000). Significant

effects were obtained with F-tests. Because densities lower than 30 tubers-m'2 varied

between spring 1999 and fall 1999 seasons, data for these seasons were analyzed

separately. Tuber densities in spring 2000 and fall 2000 were the same, so data for these

seasons were combined for analysis.

Pepper fruit yield and vegetative dry weight data were expressed as weight and as

percent weight loss relative to weight obtained with no nutsedge. Pepper fruit and

vegetative yield responses to increased tuber densities were described with polynomial

contrasts. Analysis of interactions were performed on percent loss data. Bell pepper fruit

reduction by nutsedge was regressed against tuber density using a rectangular hyperbola

model proposed by Cousens (1985): Y = ID/(1 + ID/A) where Y = yield loss, D = initial






37

tuber density, I = yield loss as D approaches 0, and A = maximum yield loss as D

approaches infinity. Values for vegetative growth responses to tuber density were

regressed using a rectangular hyperbola: Y = A x X/(B + X) where 'Y' = percent loss, 'X'

= initial tuber density, 'A' = maximum percent loss, and 'B' = a random parameter. All

curves generated with hyperbolic equations originated at zero. Responses ofnutsedge

growth parameters and shoot N concentration and uptake to increased initial nutsedge

plant density were described with polynomial contrasts.

Results and Discussion

Common planted-tuber densities in all seasons were 30, 60, and 90 tubers

tubers-m2. These tuber densities corresponded to the high range of bell pepper fruit and

vegetative yield reduction by nutsedge interference. Thus, in fall 1999, tuber densities of

10 and 20 tubers-m"2 were added and the 120 tubers'm"2 density omitted. During each

season in 2000, a density of 15 tubers-m2 was used in place of the 10 and 20 tubers-m"2

densities. Although each planted tuber may have produced more than one shoot, initial

tuber density was considered the same as initial plant density in discussion below.

Pepper Fruit Yield

Main treatment effects on pepper fruit yield are shown in Tables 1-2, 1-3, and 1-4.

In spring 1999, large, marketable, and total fruit weights as t-ha' were greater and losses

as percent of yield with pepper grown weed-free were less with pepper plants spaced 23

than 31 cm apart within rows (Table 1-2). In-row pepper spacing in fall 1999 did not

affect pepper fruit weight (Table 1-3).

In 2000, bell pepper fruit yield losses due to nutsedge interference were greater in

fall than spring (Table 1-4) due to greater early-season nutsedge vigor as explained






38

below. Season interacted with in-row pepper plant spacing on large fruit weight as t'ha1

but not as percent reduction by nutsedge interference. Nutsedge interference reduced

large fruit weight (%) to a greater extent with pepper plants spaced 31 than 23 cm apart

(Table 1-4). Marketable fruit weights were similar with in-row pepper spacings, but

percent loss of marketable fruit due to nutsedge interference was 4% greater with pepper

plants spaced 31 than 23 cm apart within rows. Pepper plants produced more total fruit

weight when grown 23 than 31 cm apart, but total fruit weight loss (%) compared to

pepper grown without nutsedge was greater with pepper plants spaced 31 than 23 cm

apart.

It appeared that increasing pepper population by reducing in-row pepper plant

spacing from 31 to 23 cm allowed pepper plants to more effectively compete with

nutsedge. Therefore, intraspecific competition of pepper with itself was not as important

as interspecific competition of pepper with nutsedge. With weeds controlled, Locascio

and Stall (1994) reported similar bell pepper yields with in-row plant spacings of 23 and

31 cm with greater yield per plant with the 31 than 23 in-row pepper spacing.

Nutsedge interference in each season in 1999 reduced bell pepper fruit yields

relative to yields obtained with pepper grown weed-free (Tables 1-2 and 1-3). Yield

responses to plant density in spring 1999 were linear (Table 1-2), but were quadratic in

fall 1999 (Table 1-3) and quadratic or cubic in 2000 (Table 1-4).

Rectangular hyperbolas generated for percent yield loss responses to nutsedge

plant density are shown in Fig. 1-1. In spring 1999, fall 1999, and in 2000, the rate of

yield loss was most rapid between 0 and 30 plants-m2. Nutsedge interference with plants

from 30 plants-m2 reduced bell pepper fruit yields by 55% to 70%. Yield losses (%)






39

continued to increase with nutsedge densities greater than 30 plants'm2, but they

increased less sharply than between 0 and 30 plants-m2. In all seasons, the critical

planted nutsedge density resulting in 10% large, marketable, or total pepper fruit weight

loss was predicted with less than 5 plants'm-2, and the biological threshold was predicted

to be 30 to 45 plants-m'2.

Coefficients for model parameters for each fruit grade are shown in Table 1-5.

Coefficients for parameter 'A' (yield loss with tuber density approaching infinity) showed

that, with continued increases in nutsedge density beyond 90 or 120 plants-m2, yield

losses were expected to plateau at 90% to 100%.

Yield loss responses to initial nutsedge plant density in 2000 were not as well

correlated (low r2 values) as those in spring 1999 and fall 1999 (Fig. l-l), possibly a result

in 2000 of regressing yield loss data within means from two seasons. Regressing the

means would have increased the r2 values. Slopes, though not as well correlated,

resembled those obtained in spring 1999 and fall 1999.

Slopes generated by Cousen's model were similar in shape to those obtained by

Morales-Payan (1999) for tomato yield loss to yellow nutsedge interference. Comparing

his results with those in the present study, however, showed that tomato was more

competitive to yellow nutsedge interference than bell pepper. For instance, the critical

nutsedge density for 10% loss of marketable bell pepper and tomato fruit yield was 5 and

12 plants-m-2, and the tuber density resulting in the biological threshold resulted in 45%

and over 60% yield loss for bell pepper and tomato, respectively. Tomato plants are taller

and form a larger leaf canopy than pepper plants and are, thus, better able to compete with

nutsedge. The low tolerance of bell pepper to yellow nutsedge interference suggested that






40

near total control of yellow nutsedge tubers is needed for acceptable pepper fruit

production.

Pepper Height

Bell pepper height data are shown in Tables 1-6, 1-7, and 1-8. In spring 1999

(Table 1-6) and fall 1999 (Tablel 1-7), in-row spacing of pepper plants had no influence on

pepper plant heights. In 2000, pepper plants at fruit harvest were taller in spring than fall

and in-row pepper spacing had no influence on pepper plant heights (Table 1-8).

In spring 1999 (Table 1-6) and fall 1999 (Table 1-7), mean nutsedge density

influenced height of peppers compared to heights with no nutsedge. In spring 1999,

pepper plants were shorter without than with nutsedge interference. In contrast, fall 1999

pepper plants were shorter with than without nutsedge interference. In 2000, nutsedge

interference had no effect on pepper plant heights (Table 1-8).

In spring 1999, initial nutsedge plant density influenced pepper plant height

during but not after pepper flowering (Table 1-6). At that time, pepper plant height

increased quadratically from 23 to 27 cm with an increase in planted nutsedge density

from 30 to 120 plants-m"2. Most of the height gain was between pepper flowering and

fruit development.

In fall 1999, at each time they were recorded, pepper plant heights declined

linearly from about 33 to 25 cm with an increase in nutsedge density from 10 to 90

plants-m2. Pepper plant heights increased little between pepper flowering and the end of

the season.

In 2000, initial nutsedge plant density interacted with season on pepper plant

height during pepper flowering and fruit development (Tables 1-8 and 1-9). At these






41
times, pepper plant heights in spring 2000 either increased or changed little while, in fall

2000, they declined in cubic or linear fashion with an increase in planted nutsedge density

from 15 to 90 plants-m2 (Table 1-9). Pepper plant heights after fruit harvest, averaged

over both seasons in 2000, changed little with an increase in initial nutsedge density from

15 to 90 plants-m2 (Table 1-8).

Pepper plant heights responded to nutsedge interference differently in spring vs.

fall seasons. In spring seasons (Tables 1-6 and 1-9), pepper plants grown with nutsedge

were able to compete with nutsedge, whereas fall-season pepper plants (Tables 1-7 and

1-9) did not appear to be able to compete with nutsedge plants. These data suggested that

pepper plants were more competitive in spring than fall.

Pepper Plant Leaf Number

Main effects of treatments on pepper leaf number are shown in Tables 1-10, 1-11,

and 1-12. In spring 1999, leaf counts were not obtained from pepper plants sampled

during pepper flowering (Table 1-10). In-row pepper plant spacing in spring 1999 only

influenced leaf number loss (%) at pepper fruit development when reduction (%) in leaf

number was greater with pepper plants spaced 31 than 23 cm apart. In fall 1999, leaf

number was not influenced by in-row pepper plant spacing (Table 1-11).

In 2000, pepper plants sampled during pepper flowering, fruit development and

after final fruit harvest produced more leaves in the spring than fall, but reductions (%) of

leaf number due to nutsedge interference were similar between seasons (Table 1-12). In-

row pepper spacing, during 2000, did not influence leaf number of plants sampled during

pepper flowering. At fruit development, leaf numbers were similar with both in-row

pepper spacings, but nutsedge interference reduced leaf number (%) to a greater extent






42

with pepper plants spaced 31 than 23 cm. At final fruit harvest, pepper had more leaves

when grown 31 than 23 cm apart, and leaf number reduction (%) was greater with pepper

plants spaced 31 than 23 cm apart.

In all seasons, nutsedge interference reduced pepper plant leaf number compared

to that with no nutsedge (Tables 1-10, 1-11, and 1-12). Leaf number responses to initial

nutsedge plant density were linear in spring 1999 (Table 1-10), quadratic in fall 1999

(Table 1-11) and linear or quadratic in 2000 (Table 1-12). Leaf numbers decreased while

leaf number reductions (%) by nutsedge interference increased with increases in planted

nutsedge density.

Rectangular hyperbolas for leaf number reduction by nutsedge interference are

shown in Fig. 1-2. At pepper flowering, leaf number loss (%) increased more sharply in

fall 1999 than in 2000 with increases in initial nutsedge plant density. In fall 1999, the

rate of leaf number loss (%) at each sampling time appeared similar while in 2000, the

rate of leaf number loss (%) was less pronounced at pepper flowering than at pepper fruit

development or after fruit harvest. At pepper fruit development and after fruit harvest, in

all seasons, leaf number loss (%) increased more sharply with an increase in planted

nutsedge density between 0 and 30 than between 30 to 90 or 120 plants'm2.

According to models for slopes in Fig 1-2, nutsedge plants from less than 5

tubers'm"2 resulted in the critical density for 10% reduction in leaf number of pepper

plants, except at pepper flowering in 2000 where 9 plants'm"2 resulted in 10% leaf

number reduction. The biological threshold was predicted to be with an initial nutsedge

density of 30 plants'm"2 for each sampling time except pepper flowering in 2000. At

pepper flowering in 2000, the biological threshold was not reached.






43

Coefficients for model parameters of rectangular hyperbolas used to describe leaf

number loss to nutsedge interference are shown in Table 1-13. Models predicted

maximum leaf number reduction by nutsedge interference of 75% to 91%.

Pepper Plant Leaf Area

Main effects of treatments on pepper plant leaf area are shown in Tables 1-14,

1-15, and 1-16. In-row spacing in spring 1999 only influenced leaf area, as cm2, of

pepper at the end of the season (Table 1-14) and had no effect in fall 1999 (Table 1-15).

At each sampling time in 2000, leaf area of spring-grown pepper plants exceeded

that of fall-grown pepper, but leaf area reduction (%) by nutsedge interference in fall and

spring was similar (Table 1-16). In-row pepper spacing in 2000 did not influence pepper

plant leaf area until pepper fruit development stage. At fruit development and at the end

of the season, leaf areas were greater with pepper plants spaced 31 than 23 cm apart, but

leaf area reductions (%) by nutsedge interference were similar with both pepper plant

spacings.

Nutsedge interference consistently reduced pepper plant leaf area compared to leaf

area with no nutsedge planted, and leaf area decreased while leaf area losses (%)

increased with increases in nutsedge plant density (Tables 1-14, 1-15, and 1-16). Leaf

area losses (%) by nutsedge interference were characterized by rectangular hyperbolas as

shown in Fig. 1-3. The rate of leaf area loss with pepper plants sampled during pepper

flowering was more pronounced in fall 1999 than in spring 1999 and spring and fall of

2000. In spring 1999, the rate of increase in pepper leaf area reduction (%) was slightly

greater for plants sampled during pepper fruit development than after fruit harvest. In fall

1999 and in spring and fall of 2000, rates of leaf area reduction (%) at fruit development






44

appeared similar as at the end of the season. Except at pepper flowering in spring 1999,

leaf area losses (%) increased most sharply (to between 40% and 60%) with an increase

in initial nutsedge density from 0 to 30 plants-m2. At pepper flowering in spring 1999,

nutsedge interference with 12 plants-m"2 reduced leaf area by 10%, and the biological

threshold was not reached. At remaining sampling times and seasons, the critical density

for 10% leaf area reduction by nutsedge interference was predicted at less than 5

plants'm'2, and the biological threshold was reached with 30 to 45 plants'm2.

Coefficients for model parameters characterizing the effect of nutsedge tuber

density on leaf area reduction by nutsedge interference are shown in Table 1-17.

Nutsedge interference was predicted to reduce leaf area by a maximum of 67% to 99%.

Pepper Leaf Dry Weight

Main effects of treatment on bell pepper leaf dry weight are shown in Tables 1-18,

1-19, and 1-20. In spring 1999, pepper plant in-row spacing did not affect pepper plant

leaf dry weight until after fruit harvest (Table 1-18). After pepper fruit harvest, pepper

plants produced more leafbiomass when spaced 31 than 23 cm apart, but nutsedge

interference reduced leafbiomass similarly with both pepper plant spacings. In fall 1999,

in-row pepper plant spacing did not influence pepper leaf dry weight (Table 1-19).

At each sampling time in 2000, leaf dry weights were greater while leaf dry

weight losses (%) were less in spring than fall (Table 1-20). In row pepper spacing in

2000 did not affect leaf dry weight of pepper plants at pepper flowering, but at fruit

development and after fruit harvest more leafbiomass (g-plant') and less leafbiomass

loss (%) resulted from the 31- than 23-cm pepper spacing.






45

Nutsedge interference consistently reduced pepper leaf dry weights relative to

weights with pepper grown weed-free (Tables 1-18, 1-19 and 1-20). Leaf dry weights

decreased while leaf dry weight losses (%) increased with increases in initial nutsedge

plant density, and responses were mostly linear in spring 1999 and quadratic in the other

seasons.

Slopes generated with rectangular hyperbola models for the effect of initial

nutsedge plant density on pepper leaf dry weight are shown in Fig. 1-4. Parameter

coefficients for these slopes are shown in Table 1-21. Slopes for leaf dry weight loss

resembled those for leaf area (Fig. 1-3). Pepper leaf dry weights at pepper flowering were

reduced by nutsedge interference, relative to that with no nutsedge, 20% and 30% with 30

plants-m2 and 40% and 60% with 90 plants'm2 in spring 1999 and in 2000, respectively.

At or after pepper fruit development in each season, leaf dry weight losses with a planted

nutsedge density of 30 plants'm2 were not greatly increased with further increases in

nutsedge density.

Models showed that at pepper flowering in spring 1999 and in 2000, bell pepper

tolerated interference by nutsedge plants from 7 to 12 tubers-m"2 without a greater than

10% reduction in leaf dry weight, and the biological threshold for leaf dry weight loss

was not reached. At flowering in fall 1999 and at or after fruit development in each

season, the critical initial nutsedge density for 10% dry weight loss was predicted with

less than 5 plants'm2, and the biological threshold was reached with 30 plants'm2.

Pepper Stem Dry Weight

Main effects of treatments on stem dry weight are shown in Tables 1-22, 1-23,

and 1-24. In spring 1999 at pepper flowering, pepper plants produced a similar amount of






46

stem biomass with both in-row spacings, but nutsedge interference at pepper flowering

and harvest times reduced stem dry weights (%) to a greater extent with plants spaced 31

than 23 cm apart (Table 1-22). Apparently, during pepper flowering, nutsedge

interference had a greater effect on stem biomass than leaf biomass production as leaf

biomass losses (%) were similar with both pepper plant spacings (Table 1-18). During

pepper fruit development in spring 1999, in-row pepper spacing had no effect on stem dry

weight (Table 1-22). After fruit harvest, plants produced more stem biomass with pepper

plants spaced 31 than 23 cm apart, but stem dry weight losses (%) were similar with both

pepper plant spacings. In fall 1999, in-row pepper spacing did not affect pepper stem dry

weights (Table 1-23).

In 2000, stem dry weights were much greater, and losses (%) were 25% to 50%

less with pepper plants grown in spring than fall (Table 1-24). In-row pepper spacing had

no or little effect on pepper stem dry weights in spring and fall 2000.

In all seasons, nutsedge interference reduced stem dry weights compared to those

with pepper grown weed-free (Tables 1-22, 1-23, and 1-24). Furthermore, in all seasons,

pepper stem dry weights decreased while dry weight losses (%) increased with increases

in initial nutsedge plant density. These responses were linear or cubic in spring 1999

(Table 1-22) and quadratic in the other seasons (Tables 1-23 and 1-24).

Slopes and model parameter coefficients for stem dry weight reduction (%) by

nutsedge interference are shown in Fig. 1-5 and Table 1-25, respectively. These slopes

appeared similar to those observed for leaf area (Fig. 1-3) and leaf dry weight (Fig. 1-4),

except that, at pepper flowering in spring 1999, stem dry weight loss increased linearly

from about 8% to 30% with an increase in initial nutsedge density from 30 to 120






47

plants-mr2. Similarly, in spring and fall 2000 during pepper flowering, stem dry weight

loss increased from 12% to 50% with an increase in nutsedge density from 15 to 90

plants-mi2. (Fig. 1-5). At flowering in fall 1999 and during or after fruit development in

each season, pepper plant stem dry weight losses (%) increased rapidly to over 45% with

an initial nutsedge density of 30 plants-m2 and less sharply with further increases in

nutsedge plant density.

Bell pepper plants sampled during flowering in spring 1999 and in 2000 tolerated

nutsedge interference with plants from 10 and 33 planted tubers-m"2, respectively, without

a greater than 10% reduction in stem dry weight. In these seasons, the biological

threshold for leaf dry weight loss was not reached. At flowering in fall 1999 and during

or after fruit development in each season, the critical initial nutsedge density for 10% loss

and biological threshold was predicted with less than 5 plants-m2 and with 30 plants-m2,

respectively.

Pepper Fruit Dry Weight During Fruit Development Stage

Main effects of treatments on dry weight of fruit present on pepper plants sampled

during fruit development are shown in Tables 1-26 and 1-27. In spring 1999, fruit dry

weights were similar with both in-row pepper plant spacings, but percent dry weight loss

of 75% with pepper plants spaced 31 cm apart was slightly greater than that with plants

spaced 23 cm apart (Table 1-26). In fall 1999, in-row pepper spacing had no effect on dry

weight of developing fruit.

In 2000, during the pepper fruit development stage, fruit dry weights were much

greater in spring than fall, but percent losses of approximately 60% were similar in both






48

seasons (Table 1-27). In-row pepper spacing in spring and fall 2000 did not influence dry

weight of enlarging fruit.

In all seasons, nutsedge interference substantially reduced fruit dry weights

compared to those with no nutsedge (Tables 1-26 and 1-27). Fruit dry weights decreased

whereas losses (%) increased with increases in nutsedge plant density. These responses

to nutsedge density were linear in spring 1999 and quadratic in the other seasons.

Rectangular hyperbolas and coefficients for model parameters are shown in Fig.

1-6 and Table 1-28, respectively. Slopes for each season were similar in shape and

magnitude (Fig. 1-6). In each season, percent dry weight loss of developing fruit

increased rapidly to nearly 60% with nutsedge interference from 30 plants-m2 and

increased more slowly to between 70% and 80% with 90 or 120 plants-m'2. Thus, in all

seasons, the critical nutsedge density for 10% reduction in dry weight and the biological

threshold was predicted with less than 5 and with 30 plants-m2, respectively.

Rectangular hyperbolas for developing (Fig. 1-6) and harvested (Fig. 1-1) fruit

weight as well as fruit number (data not shown) were similar. Therefore, nutsedge

interference significantly reduced bell pepper fruit set and enlargement.

Pepper Plant Total Dry Weight

Main effects of treatments on total bell pepper dry weight [sum of leaf, stem, and

fruit (if present) dry weight] are shown in Tables 1-29, 1-30, and 1-31. In spring 1999

during pepper flowering, in-row pepper spacing did not influence total biomass produced

by pepper plants, but percent loss of biomass due to nutsedge interference was greater

with pepper plants spaced 31 than 23 cm apart (Table 1-29). During pepper fruit

development, in-row pepper spacing had no influence on total pepper plant biomass.






49

After final pepper fruit harvest, total dry weight of pepper plants was slightly greater with

pepper plants spaced 31 than 23 cm apart, and biomass loss (%) due to nutsedge

interference was similar with both in-row pepper plant spacings. In fall 1999, in-row

pepper spacing had no influence on the dry weight of total biomass produced by pepper

plants (Table 1-30).

In 2000, total pepper biomass was greater and biomass loss (%) was less in spring

than fall (Table 1-31), and this was consistent with results in 1999. For example, at

pepper flowering, nutsedge interference reduced total pepper biomass by 30% to 41% in

spring 1999 (Table 1-29) compared to 63% to 64% in fall 1999 (Table 1-30). These

findings were in agreement with those for all pepper growth parameters and showed that

nutsedge interfered more strongly with bell pepper vegetative growth in fall than spring.

In spring and fall 2000, in-row spacing of pepper plants had little or no effect on

the dry weight of total biomass produced by pepper plants at or after pepper flowering

(Table 1-31). This was also true for pepper leaf, stem and developing fruit dry weights in

2000 and for pepper growth parameters in fall 1999. Therefore, only in spring 1999 did

increased pepper plant populations with plants spaced 23 cm compared to 31 cm apart

improve pepper plant competitiveness against yellow nutsedge. In all seasons, however,

yellow nutsedge interference substantially reduced bell pepper plant growth.

As for previously discussed growth parameters, nutsedge interference reduced

total pepper biomass in all seasons compared to that with no nutsedge (Tables 1-29, 1-30,

and 1-31). Therefore, yellow nutsedge interference significantly reduced bell pepper fruit

yield and plant size.






50

Total pepper plant biomass decreased while biomass loss (%) increased with

increases in nutsedge plant density (Tables 1-29, 1-30, and 1-31). As for other growth

parameters previously discussed, these nutsedge density effects were usually linear in

spring 1999 (Table 1-29) and quadratic or cubic in the other seasons (Tables 1-30 and 1-

31).

Rectangular hyperbolas and coefficients for model parameters describing the

effects on initial nutsedge plant density on total pepper biomass are shown in Fig. 1-7 and

Table 1-32, respectively. The shape and magnitude of slopes shown in Fig. 1-7

resembled those for leaf number (Fig. 1-2), leaf area (Fig 1-3), and dry weight of leaves

(Fig. 1-4) and stems (Fig. 1-5). The effects of nutsedge interference on pepper growth in

spring 1999 and in 2000, as shown by data for these variables, were more obvious during

and after pepper fruit development than during pepper flowering. This was evidenced by

higher coefficient of determination (r2) values for data obtained during than after pepper

flowering. Even at 6 WAT during pepper flowering, however, nutsedge interference

substantially reduced pepper plant size, especially with 30 or more plants-m2. For

instance, total pepper plant biomass of pepper plants sampled 6 WAT in spring 1999 and

in 2000 was reduced by over 45% with 90 nutsedge plants'm'2 (Fig. 1-7).

Interspecific nutsedge competition with pepper was dominant during pepper

flowering in spring 1999 and in 2000 as shown by linear or nearly linear increases in

biomass loss with increases in nutsedge plant density (Figures 1-4, 1-5, and 1-7). During

and after pepper fruit development in spring 1999 and in spring and fall 2000, loss

percentages for each pepper growth parameter increased less sharply with an increase in

initial nutsedge density from 30 to 90 or 120 than between 0 and 30 plants'm2.






51

Intraspecific nutsedge competition, therefore, increased with time from pepper flowering

to fruit development and with increases in nutsedge plant density from 30 to 90 or 120

plants-m'2. By pepper flowering in fall 1999, however, nutsedge had already substantially

interfered with bell pepper growth as indicated by high percent losses for pepper growth

parameters and by higher r2 values obtained for plants sampled during than after pepper

flowering.

For all growth parameters discussed above, the highest r2 values were obtained

when nutsedge interference with pepper growth was most severe. At remaining times,

low r2 indicated that nutsedge interference did not consistently result in the losses (%)

indicated by the regression models.

Pepper Plant and Fruit N Concentration

Concentration of N in bell pepper plant tissues was measured to determine ifN

was a common resource competed for by yellow nutsedge and bell pepper. Main effects

of treatments on bell pepper N concentration in plant (leaf and stem tissue) and fruit

tissue are shown in Tables 1-33, 1-34, and 1-35. In-row pepper plant spacing did not

influence pepper plant and fruit N concentration in spring 1999 (Table 1-33). In fall

1999, plant N concentrations were slightly greater with pepper plants grown 31 than 23

cm apart within rows, but in-row pepper plant spacing did not affect pepper fruit N

concentration (Table 1-34).

In 2000, season had no effect on pepper plant N concentration during pepper

flowering, but plant N concentrations after pepper flowering were greater in fall than

spring (Table 1-35). In-row pepper plant spacing in 2000 did not affect pepper plant N or

developing fruit N concentration. Harvested fruit N concentrations, however, were 10%






52

greater with pepper plants spaced 23 than 31 cm apart within rows, a result consistent

with that of less yield loss (%) with pepper plants spaced 23 than 31 cm apart (Table 1-4).

Nutsedge interference in spring 1999 reduced plant N concentration, relative to

that with plants grown weed-free, during pepper flowering and after final fruit harvest but

not during fruit development (Table 1-33). Nutsedge interference had no effect on pepper

fruit N concentration in spring 1999. In fall 1999, nutsedge interference appeared to

increase concentrations of N in vegetative tissue of pepper plants sampled after fruit

harvest and in harvested fruit (Table 1-34). In spring and fall 2000, plant and fruit N

concentrations were greater without than with nutsedge interference, except for end-of-

season plant N concentration that was not influenced by nutsedge (Table 1-35).

In spring 1999, during pepper flowering, pepper plant N concentration declined

linearly from 4.22% to 3.72% with an increase in nutsedge plant density from 30 to 120

plants-m"2 (Table 1-33). Tuber density did not differentially influence pepper plant N

concentration during pepper fruit development, but N concentration after fruit harvest

declined linearly from 1.85% to 1.56% with an increase in initial nutsedge density from

30 to 120 plants'm'2. Concentrations of N in immature and harvested fruit were similar

with all planted nutsedge densities.

With an increase in initial nutsedge density from 10 to 90 plants.mn2 in fall 1999,

N concentration in pepper plant tissue sampled during pepper flowering increased linearly

from 2.80% to 3.46% (Table 1-34). During pepper fruit development, the effect of

nutsedge plant density on pepper plant N concentration was quadratic, but changes in N

concentration over the range of tuber densities used were slight. After pepper fruit

harvest, pepper plant N concentration increased linearly from 2.17% to 2.74% with an






53

increase in initial nutsedge density from 10 to 90 plants'm2. Nitrogen concentration in

immature pepper fruit decreased linearly from 1.97% to 1.62% while N concentration in

harvested fruit remained constant with an increase in nutsedge density from 10 to 90

plants-m'2.

In 2000, at pepper flowering, plant N concentrations decreased quadratically from

2.85% to 2.55% with an increase in initial nutsedge density from 15 to 90 plants-m'2

(Table 1-35). Pepper plant N concentrations after pepper flowering were not differentially

influenced by nutsedge interference at the tuber densities used.

In 2000, season and initial nutsedge density interacted in their effects on

developing and harvested pepper fruit N concentration (Tables 1-35 and 1-36). Nutsedge

interference reduced fruit N concentration with the exception of N concentration in

harvested spring-season fruit (Table 1-36). The major source of the interaction was that

N concentrations in immature and harvested fruit changed little in spring and decreased in

fall with increases in planted nutsedge density. Linear decreases in immature and

harvested fall-season fruit N concentrations with increases in initial nutsedge plant

density were due to the absence of fruit on some pepper plants grown with nutsedge.

According to Lorenz and Maynard (1988), 2.5% to 3.5% N of leaf dry weight was

sufficient for pepper plants at the full bloom stage. In the present study, plant (leaf and

stem tissue combined) N concentrations with no nutsedge interference at 6 WAT were

4.7%, 2.9%, and 3.1% in spring 1999 (Table 1-33), fall 1999 (Table 1-34), and spring and

fall 2000 (Table 1-35), respectively. During pepper fruit development and after fruit

harvest, leafN concentrations were up to 60% greater than stem N concentrations (data

not shown). Therefore, N concentration at 6 WAT in leaf tissue alone would have been






54

greater than that with leaf and stem tissue combined. Thus, it appeared that pepper plants

grown without nutsedge interference during each season contained a sufficient amount of

N at 6 WAT.

Lorenz and Maynard (1988) reported a N sufficiency range for bell pepper of

1.5% to 2.5% dry weight of leaf tissue sampled at full bloom with fruits 75% of full size.

Miller (1961) showed that 1.75% N of dry weight of fruit tissue was sufficient for bell

pepper fruit. In the present study, spring-season pepper plant and fruit N concentrations

during pepper flowering and fruit development were at least 2.28% (Tables 1-33 and 1-

35). Therefore, nutsedge interference did not reduce pepper plant N concentration to a

growth limiting concentration in spring seasons. The linear reduction of pepper plant N

concentration in spring 1999 with increases in nutsedge plant density (Table 1-33)

indicated that nutsedge competed with pepper for N. Therefore, under conditions of low

soil fertility, nutsedge interference with pepper could reduce pepper growth and yield by

reducing the amount of N available for pepper plants.

In fall seasons, plant N concentrations of at least 2.02% during pepper fruit

development (Tables 1-34 and 1-35) exceeded 1.5%, the lowest concentration of N

reported to be sufficient for pepper growth by Lorenz and Maynard (1988). Harvested

fruit N concentration in fall 1999 exceeded 1.75% (Table 1-34), a sufficient concentration

of N (Miller, 1961). In fall 2000, fruit N concentrations of less than 1.75% were

observed (Table 1-36), but this was due to the lack of fruit in some plots that received

nutsedge. Therefore, in fall seasons, N availability to pepper plants may have been

reduced by nutsedge interference to growth limiting amounts, but N concentration data

were not conclusive.








Pepper Plant N Uptake

Main effects of treatments on pepper plant (leaf plus stem) N uptake are shown in

Tables 1-37, 1-38, and 1-39. In spring 1999, in-row pepper spacing influenced pepper

plant N uptake at pepper flowering and fruit development but not at the end of the season

(Table 1-37). At pepper flowering and fruit development, N accumulations in pepper

plants were greater with pepper plants spaced 23 than 31 cm apart within rows. Loss (%)

of N uptake at pepper flowering, however, was greater with pepper plants spaced 31 than

23 cm apart within rows. After pepper flowering in-row pepper spacing had no effect on

pepper plant N accumulation.

In-row pepper spacing in fall 1999 did not influence pepper plant N uptake and

only influenced plant N uptake reduction (%) by nutsedge interference at pepper fruit

development (Table 1-38). At this time, nutsedge interference reduced pepper plant N

uptake to a greater extent with pepper plants grown 31 than 23 cm apart within rows.

In 2000, spring-grown pepper plants sampled at each pepper growth stage had

accumulated more plant N than those grown in fall (Table 1-39). Reduction (%) of plant

N uptake, relative to that with no nutsedge, was similar in spring and fall at the pepper

flowering stage. At the pepper fruit development stage, reduction (%) of plant N uptake

by nutsedge interference was greater in fall than spring.

In 2000, pepper plant N accumulations at flowering and after fruit harvest were

greater with plants spaced 23 than 31 cm apart, but in-row plant spacing had no effect on

N uptake at fruit development (Table 1-39). Reduction (%) in plant N uptake at

flowering was similar with plants spaced 23 than 31 cm, but at fruit development it was

greater with plants spaced 31 than 23 cm apart. After pepper fruit harvest, season






56

interacted with in-row pepper plant spacing on pepper plant N uptake reduction (%) by

nutsedge interference (Tables 1-39 and 1-40). In both seasons, nutsedge interference

reduced pepper plant N uptake by at least 57%, but only in spring was the reduction

percentage greater with pepper plants spaced 31 than 23 cm apart (Table 1-40).

During each season, nutsedge interference consistently reduced pepper plant N

uptake compared to that with no nutsedge (Tables 1-37, 1-38, and 1-39). With increases

in initial nutsedge plant density, pepper plant N uptake decreased while percent reduction

of N uptake increased. An exception occurred in spring 1999 during pepper fruit

development when pepper plant N uptake reduction by nutsedge interference remained

constant at about 60% with all initial nutsedge plant densities (Table 1-37).

In spring 1999, nutsedge interference with plants from 30 tubers-m'2 reduced

pepper plant N uptake by 27% at pepper flowering compared to 57% and 52% during

fruit development and after fruit harvest, respectively (Table 1-37). With further

increases in initial nutsedge density, plant N reduction percentages increased more

sharply during than after pepper flowering.

With an initial nutsedge density of 10 plants-m"2 in fall 1999, nutsedge

interference reduced pepper plant N uptake by at least 19%, and the effects of nutsedge

interference were most obvious at pepper flowering when plant N uptake reduction

increased from 38% to 82% with an increase in nutsedge density from 10 to 90 plants-m"2

(Table 1-38).

In 2000, nutsedge interference with 15 plants-m"2 reduced pepper plant N uptake

by 24% at pepper flowering compared to 46% and 48% during pepper fruit development

and after fruit harvest, respectively (Table 1-39). Nutsedge interference reduced pepper






57

plant N uptake in 2000 more severely after than during pepper flowering. In each season,

at one or more of the pepper growth stages, nutsedge interference reduced pepper plant N

uptake to a maximum of 70% or more (Table 1-37, 1-38, and 1-39).

During each season, coefficients of determination for plant N accumulation as

percent loss of that with pepper grown weed-free were below 0.50. Slopes for plant N

uptake reduction by nutsedge interference were not shown because the critical density for

10% reduction in plant N uptake could not be accurately predicted.

Pepper Fruit N Uptake

Main effects of treatments on pepper fruit N uptake are shown in Tables 1-41, 1-

42, and 1-43. In spring 1999, pepper fruit in the development stage accumulated more N

with pepper plants spaced 23 than 31 cm apart, but N uptake as percent loss, relative to

that obtained with pepper grown weed-free, was similar with both pepper plant spacings

(Table 1-41). Harvested fruit N uptake was slightly greater with pepper plants spaced 23

than 31 cm apart within rows, and N uptake reduction percentage was greater with pepper

plants spaced 31 than 23 cm apart.

In fall 1999, in-row pepper spacing did not have a strong effect on pepper fruit N

uptake (Table 1-42). Reduction of N (%) in immature fruit was greater with pepper

plants spaced 31 than 23 cm apart within rows.

In 2000, immature and harvested pepper fruit accumulated about ten times more N

in spring than fall, but reduction (%) of N taken up by immature fruit, relative to that with

no nutsedge, was similar between seasons (Table 1-43). Harvested fruit N uptake

reduction percentages were greater in fall than spring.






58

In-row pepper spacing in 2000 (Table 1-43) influenced developing and harvested

fruit N uptake and N uptake reduction (%) by nutsedge interference in a similar manner

as described in spring 1999 (Table 1-41). During spring 1999 (Table 1-41), fall 1999

(Table 1-42), and spring and fall of 2000 (Table 1-43), nutsedge interference reduced

immature and harvested fruit N accumulation by at least 57% with either in-row pepper

plant spacings.

In each season, nutsedge interference reduced immature and harvested fruit N

uptake compared to that with no nutsedge (Tables 1-41, 1-42, and 1-43). Fruit N uptake

decreased while N uptake reduction percentages increased with increases in nutsedge

density. Initial nutsedge plant density effects on immature and harvested fruit N uptake

were linear in spring 1999 (Table 1-41) and quadratic in the other seasons (Tables 1-42

and 1-43).

Rectangular hyperbolas for fruit N uptake reduction by nutsedge interference and

coefficients for model parameters are shown in Fig 1-8 and Table 1-44, respectively. In

each season the slopes for developing (immature) and harvested pepper fruit N uptake

reduction by nutsedge interference were similar in shape and magnitude. They showed

that most reduction in N uptake by pepper fruit of 50% to 60% occurred as initial

nutsedge density was increased from 0 to 30 plantsm2 (Fig. 1-8). With 90 nutsedge

plants'm2, nutsedge interference reduced immature and harvested fruit N uptake by at

least 70% in each season. In each season, the critical densities (for 10% reduction) and

biological thresholds for immature and harvested fruit N uptake reduction by nutsedge

interference were reached with less than 5 plants-m2 and with 30 plants-m2, respectively.








Pepper Plant Plus Fruit N Uptake

Main effects of treatments on pepper plant plus fruit (total) N uptake during

pepper fruit development and harvest time are shown in Tables 1-45, 1-46, and 1-47. In

spring 1999, at pepper fruit development, plants accumulated more N when grown 23

than 31 cm apart, but reduction (%) of total N uptake by nutsedge interference was

similar with both pepper plant in-row spacings (Table 1-45). Total pepper N uptake at

harvest time was similar with both in-row pepper plant spacings while N uptake reduction

(%) by nutsedge interference was 7% greater with pepper plants spaced 31 than 23 cm

apart. In fall 1999, the only time in-row pepper spacing influenced total pepper N

uptake was at fruit development when total N uptake reduction (%) was greater with

plants spaced 31 than 23 cm apart (Table 1-46).

In 2000, at both sampling times, total N uptake was greater and reduction (%) by

nutsedge of total pepper N uptake was less in spring than fall (Table 1-47). At pepper

fruit development, bell pepper accumulated more total N when grown 23 than 31 cm

apart within rows, but nutsedge interference reduced total pepper N uptake similarly with

both in-row pepper plant spacings. Cumulative N uptake of pepper vegetative and fruit

tissue at harvest time was greater with pepper plants spaced 23 than 31 cm apart, and

reduction (%) of total pepper N uptake by nutsedge interference was 4% greater with

pepper plants spaced 31 than 23 cm apart.

In each season and at each sampling time within seasons, nutsedge interference

reduced total pepper N accumulation relative to that with no nutsedge (Tables 1-45, 1-46,

and 1-47). Total N uptake decreased with increases in nutsedge plant density in each

season. Percent reduction in total pepper N uptake increased linearly in spring 1999






60

(Table 1-45), quadratically in fall 1999 (Table 1-46), and in cubic fashion in spring and

fall of 2000 (Table 1-47) with increases in nutsedge plant density.

Rectangular hyperbolas and model parameter coefficients generated for percent

reduction by nutsedge interference of total pepper N accumulation are shown in Fig. 1-9

and Table 1-48, respectively. In each season, rates of increase in total N uptake reduction

(%) with increases in nutsedge plant density were similar at pepper fruit development as

at fruit harvest. Within each season, slopes for fruit N uptake (Fig. 1-8) and total N

uptake (Fig. 1-9) reduction by nutsedge interference were similar in shape and magnitude.

Hence, discussion and predicted parameters for fruit N uptake are applicable for total

pepper N uptake.

Nitrogen accumulation by bell pepper was a function of plant dry weight and N

concentration. Therefore, nutsedge competition reduced N uptake similarly as plant dry

weight. Nutsedge interference consistently reduced pepper plant size and, thus, N uptake

by pepper vegetative and fruit tissue.

Nutsedge Shoot Height and Number

Main effects of treatments on nutsedge shoot height and number in spring 1999,

fall 1999, and spring and fall of 2000 are shown in Tables 1-49, 1-50, and 1-51,

respectively. In spring 1999, in-row pepper plant spacing had no effect on shoot height,

and only affected shoot number at pepper fruit harvest time when the number of shoots in

a 0.1 m2 area was 10% greater with pepper plants spaced 31 than 23 cm apart (Table 1-

49). In fall 1999, in row pepper plant spacing only affected nutsedge shoot numbers

during pepper fruit development (Table 1-50). At that time there were seven more

nutsedge shoots per 0.1 m2 with pepper plants spaced 31 than 23 cm apart within rows.






61

In 2000, at pepper fruit development and fruit harvest, nutsedge shoot heights and

numbers were greater in spring than fall (Table 1-51). These results were consistent with

those obtained in spring 1999 (Table 1-49) vs. those in fall 1999 (Table 1-50). They

showed that nutsedge proliferation and growth declined with time during fall seasons.

Nutsedge shoots during pepper flowering in 2000 were less than 2 cm taller with

pepper plants spaced 23 than 31 cm apart (Table 1-51). This was the only significant

effect of in-row pepper plant spacing in 2000. Therefore, in-row pepper spacing did not

have a strong effect on nutsedge shoot proliferation and height in any of the seasons

during which the experiment was conducted.

In spring 1999, nutsedge shoot height during pepper flowering increased linearly

from 45 to 53 cm with an increase in nutsedge density from 30 to 120 plants-m2 (Table 1-

49), indicating that nutsedge competed with itself for light as the initial tuber population

was increased. During pepper fruit development and after fruit harvest, nutsedge shoot

heights were taller than during pepper flowering but not differentially influenced by

nutsedge plant density. Nutsedge shoot number, however, increased linearly with an

increase in initial nutsedge density from 30 to 120 plants'm"2 during pepper fruit

development and after fruit harvest. At pepper fruit harvest time, nutsedge shoot heights

were only slightly taller than those during pepper fruit development due to the tendency

for nutsedge leaf blades to lay over as they lengthened.

Nutsedge plant density did not differentially influence nutsedge shoot height

during pepper flowering in fall 1999 (Table 1-50), but shoot number increased linearly

from 58 to 68 shoots- 0.1m2 with an increase in initial nutsedge plant density from 10 to

90 plants'm-2. Nutsedge shoot height and number during pepper fruit development






62

responded similarly to increases in nutsedge density as during pepper flowering. At fruit

harvest, nutsedge shoot heights increased quadratically with increases in planted nutsedge

density, but changes in height with increasing nutsedge density were slight. Shoot

numbers at pepper fruit harvest time increased linearly with increases in nutsedge density.

At pepper flowering in 2000, season interacted with initial nutsedge density on

nutsedge shoot height and number (Tables 1-51 and 1-52) primarily because shoot heights

and numbers were greater in fall than spring (Table 1-52). During pepper fruit

development in 2000, nutsedge shoot height responded quadratically to increases in

nutsedge density, but changes in height were small (Table 1-51). Shoot number at this

time increased linearly from 90 to 117 shoots 0. 1m2 with an increase in planted nutsedge

density from 15 to 90 plants-m"2. At harvest time in 2000, shoot height was not

differentially influenced by increases in nutsedge density, and shoot number increased

linearly from 75 to 101 shoots'0.1 m-2 with an increase in initial nutsedge density from 15

to 90 plants'm-2.

Yellow nutsedge leaves are typically 20 to 90 cm long (Wills, 1987). In the

present work, leaf blade height and not length was measured. However, a leaf blade

length of 90 cm was in agreement with nutsedge leaf blade heights of up to 70 cm

observed in these studies. Nutsedge leaf blade heights were consistently taller than

pepper plants which were tallest in spring 1999 and did not exceed 56 cm.

Nutsedge leaf blade heights remained similar or decreased with time from fruit

development to harvest time each season. This was due to the tendency for nutsedge leaf

blades to lay over as they lengthen. The observation that nutsedge shoot counts decreased

with time in fall 1999 (Table 1-50) and fall 2000 (Table 1-51) but not in spring seasons






63

indicated that nutsedge growth was sensitive to photoperiod. According to Jansen (1971),

yellow nutsedge vegetative growth is favored by long days characteristic of those in the

spring. As daylength decreases in the fall, flowering and tuber formation dominate over

vegetative growth (Jansen, 1971; Williams, 1982).

Morales-Payan (1999) reported the development of about 700 yellow nutsedge

shoots-m2 from 90 to 120 planted tubers-m"2 at 13 weeks after tomato transplanting in fall

1995 and spring 1996. In spring 1999 in the present study, yellow nutsedge shoot

numbers at 13 WAT were about four times greater (2870 shoots-m-2) with 120 tubers-m2

than numbers reported by Morales-Payan. End-of-season yellow nutsedge shoot numbers

in the present study during fall 1999 were less than while those in spring and fall of 2000

were 31% greater than those reported by Morales-Payan (1999). In most seasons,

therefore, yellow nutsedge was more prolific when grown with bell pepper than tomato.

This was likely due to larger size of tomato than pepper plants. With 90 tubers-m2, end-

of-season pepper plant dry weights (Tables 1-29, 1-30, and 1-31) were much less than

tomato plant dry weights reported by Morales-Payan (1999).

Nutsedge N Concentration and Uptake

Main effects of treatments on nutsedge shoot N concentration and uptake in spring

1999, fall 1999, and in 2000 are shown in Tables 1-53, 1-54, and 1-55, respectively. In

spring and fall 1999, in-row pepper spacing had no effect on nutsedge shoot N

concentration and uptake (Tables 1-53 and 1-54).

In 2000, N concentrations in shoots at pepper flowering were higher in spring than

fall, but fall-season nutsedge shoots accumulated 30% more N than those in the fall

(Table 1-55). As nutsedge shoot N concentration in the fall was only 1.4%, nutsedge






64

efficiently utilized N. Later in the season, at pepper fruit development, nutsedge

concentrations were similar between seasons and spring-planted nutsedge accumulated

more N than fall-planted nutsedge. At fruit harvest, nutsedge shoots had accumulated

more N in spring than fall. This was further evidence of the decline in nutsedge vigor

over time in fall seasons.

In-row pepper spacing in 2000 did not influence yellow nutsedge shoot N

concentration and uptake (Table 1-55). Thus, an increase in pepper plant population by

spacing plants 23 compared to 31 cm apart did not reduce nutsedge shoot N concentration

or uptake.

In spring 1999, N concentration in nutsedge shoots sampled during pepper

flowering declined linearly from 2.65% to 2.37% with an increase in initial nutsedge

density from 30 to 120 plants-m2 (Table 1-53). This was possibly a result of increased

intraspecific nutsedge competition with increases in nutsedge density. Nutsedge shoot N

concentration and uptake at pepper fruit development did not respond differentially to

increases in nutsedge density. At pepper fruit harvest time, however, nutsedge shoot N

concentration declined linearly from 1.25% to 1.04% while shoot N uptake increased

quadratically with an increase in initial nutsedge density from 30 to 120 plants-m'2.

At each sampling time in fall 1999, nutsedge shoot N concentration decreased

linearly or quadratically while N uptake did not change with an increase in initial

nutsedge density from 10 to 90 plants-m'2 (Table 1-54). In fall 1999, yellow nutsedge

leaves turned yellow by the end of the season, a result of a late planting date. This

observation was in agreement with nutsedge shoot N concentrations of below 1% at

pepper harvest time.






65

Nitrogen concentration in nutsedge shoots at pepper flowering in 2000 decreased

linearly from 1.99% to 1.72% while N uptake increased linearly from 39 to 75 kg'ha'

with an increase in initial nutsedge density from 15 to 90 plants-m2 (Table 1-55).

Nutsedge shoot N concentrations at pepper fruit development were not influenced by

nutsedge density, but accumulation of N by nutsedge shoots increased linearly from 82 to

124 kg'ha' with an increase in nutsedge density from 15 to 90 plants-m2.

Season interacted with initial nutsedge density in 2000 on N concentration in

nutsedge shoots at pepper fruit harvest time (Tables 1-55 and 1-52). In spring, nutsedge

shoot concentrations were constant at 0.71% to 0.76% with increases in nutsedge

density, whereas nutsedge shoot N concentration in fall increased linearly from 0.61% to

0.76% with an increase in initial nutsedge density from 15 to 90 plants'm-2. As nutsedge

shoots in spring and fall 2000 were mostly green at harvest time, and shoot N

concentrations were below 1%, nutsedge appeared to be an efficient user of N. Nutsedge

shoot N uptake at the end of the season increased linearly from 35 to 53 kg-ha' as

nutsedge density was increased from 15 to 90 plants-m'2 (Table 1-55).

Morales-Payan (1999) found that yellow nutsedge accumulated 151 kg-ha-1 I of N

at the 13'h week of interference with tomato with an initial density of 100 plants-m"2. This

amount of N was similar to (Table 1-53) or greater than (Tables 1-54 and 1-55) the

amount of N taken up by yellow nutsedge at the end of the season in the present study

with 90 nutsedge plants-m2.

During each season, especially during pepper flowering time, nutsedge shoots

accumulated more N than pepper plants. Furthermore, nutsedge shoot N accumulation

increased while pepper N accumulation decreased with increases in planted nutsedge






66
density. This did not necessarily mean, however, that the main resource being competed

for was N. Competition for another common resource could have reduced pepper plant

size and dry weight, thereby reducing N accumulation.

Nutsedge Shading of Pepper in 2000

Season and in-row pepper spacing effects on interception of light by nutsedge

were contained in interactions as shown in Table 1-56. At pepper flowering, initial

nutsedge density interacted with season on nutsedge shading of pepper (Tables 1-56; Fig.

1-10). Slopes generated by regression analysis appeared linear (Fig. 1-10). During each

season, the percentage of available light blocked by nutsedge leaf blades increased with

an increase in nutsedge density from 15 to 90 plants-m2, but the magnitude of light

intercepted by nutsedge was much greater in fall than spring. In spring, nutsedge

intercepted about 10% to 40% of available light, whereas, in fall, nutsedge intercepted

50% to 85% of available light.

Although season and initial nutsedge density interacted in their effects on

nutsedge shading of bell pepper, season did not interact with nutsedge density on pepper

fruit yield loss in 2000 (Table 1-6). It is likely, therefore, that even with less shading of

pepper by nutsedge at flowering time in spring than fall, spring-grown pepper was shaded

sufficiently to substantially reduce pepper fruit yield.

At pepper flowering, initial nutsedge density also interacted with pepper spacing

on nutsedge shading of pepper (Table 1-56; Fig. 1-10; Table 1-57). The percentage of

available light intercepted by nutsedge increased at a slightly more rapid rate with pepper

plants spaced 23 than 31 cm apart within rows (Fig 1-10). Coefficients of determination






67

(r2 values) for these slopes were low, but nutsedge leaf blades intercepted as much as 55%

of the available light with both pepper spacings.

At pepper fruit development, the effect of initial nutsedge density on nutsedge

shading of pepper varied with season and pepper spacing (Table 1-56; Fig. 1-11; Table 1-

57). Within each season, the rate of increase in nutsedge light interception with increases

in planted nutsedge density differed with in-row pepper plant spacing. However, there

was a more noticeable difference in the magnitude of light intercepted by nutsedge in

spring compared to fall. In spring, nutsedge leaves intercepted between 40% and 60% of

available light with nutsedge densities between 45 and 90 plants'm2. With the same

nutsedge densities, fall-grown nutsedge shoots intercepted nearly 80% of available light.

As nutsedge shoots grew taller than pepper plants and significantly shaded pepper

plants, it appeared that nutsedge and pepper plants were primarily competing for light.

This conclusion was further evidenced by the tendency for spring-grown pepper plants in

1999 to grow taller when subjected to nutsedge interference than when grown weed-free

(Table 1-6). In fall 1999, pepper plants were less competitive than in spring 1999 and,

hence, did not increase in height with increases in initial nutsedge plant density (Table 1-

7). Although nutsedge may have also competed with pepper for N, evidence for this was

not as conclusive as evidence suggesting that nutsedge competed strongly with pepper for

light. The apparent sensitivity of pepper to shading was in agreement with other reports

where shading reduced pepper flower number and subsequent fruit yield (Jeon and

Chung, 1982; Shifriss et al., 1994).









Table 1-1. Dates during each season in 1999 and 2000 for planting and events at
pepper flowering, fruit development, and at or nearly at fruit harvest.

1999 2000
Spring Fall Spring Fall
Planted pepper 24 March 2 Sept. 23 March 16 Aug.
Planted nutsedee 24-25 March 30 Aug. 22 March 16-17 Aug.


Pepper ht measured

Nutsedge shoots
counted and sampled


Plant ht measured
Nutsedge shoots
counted and sampled


Vst: Fruit no. and wt.
recorded

2nd: Fruit no. and wt.
recorded


Plant ht measured'

Nutsedge shoots
counted and sampled


3 May

data not
obtained


2 June
2 June




16 June


25 June




24 Ji

24 Ji


At late pepper flowering
12 Oct. 4 May


12 Oct.


4 May


At pepper fruit development
1 Nov. 30 May 1
2 Nov. 30 May 1


At first and second pepper fruit harvest

22 Nov. 9 June


25 June 1


26 Sept.

26 Sept.


18 Oct.
17 Oct.




5 Nov.


5 Nov.


Nearly at or after final pepper fruit harvest

me 23 Nov. 28 June 15 Nov.

me 24 Nov. 28-29 June 20 Nov.


Pepper plants sampled 30 June 29 Nov.
'Pepper plant and nutsedge shoot heights were obtained.


26-27 June


15 Nov.


w








Table 1-2. Main effects of in row bell pepper plant spacing and initial yellow nutsedge
tuber density on large, marketable, and total pepper fruit weight in spring 1999.
Pepper fruit yield (t-ha' and % loss)
Large Marketable Total
Treatment t-ha' % loss t-ha,' % loss t-ha' % loss
Pepper spacing (cm)
23 20.89 64 25.60 62 27.58 65
31 17.93 72 22.47 72 24.74 73
Signif. ** ** ** *** ** ***
Tuber density
(TD; no-m2)
0 42.59 51.92 58.85 -
30 19.05 55 24.14 54 25.23 57
60 14.49 66 18.00 65 18.98 68
90 12.63 70 15.78 69 16.65 71
120 8.28 80 10.33 80 11.09 81
0 vs. nutsedge *** *** ***
TD (30 to120) *** *** ***
ZValues were expressed as percent loss relative to those obtained with pepper grown
weed-free (0 TD).
NS, **. **Effects were nonsignificant or significant at P < 0.01 or 0.001, respectively,
according to F tests. Competition (TD from 30 to 120) vs. no competition (0 TD)
effects were tested with contrasts. Tuber density effects were linear (L) according to
polynomial contrasts.








Table 1-3. Main effects of in row bell pepper plant spacing and initial yellow nutsedge
tuber density effects on large, marketable, and total pepper fruit weight in fall 1999.
Pepper fruit yield (t-ha' and % loss)
Large Marketable Total
Treatment t-ha' % loss' t-ha' % loss' tha' % loss
Pepper spacing (cm)
23 4.66 74 6.20 66 7.04 64
31 4.62 74 6.23 67 6.75 67
Signif. NS NS NS NS NS NS
Tuber density
(TD; no-i'2)
0 11.82 13.79 15.15 -
10 7.73 38 9.58 33 10.21 34
20 5.25 56 7.07 48 7.55 50
30 2.33 84 4.53 69 5.20 67
60 0.51 95 1.50 87 2.15 84
90 0.21 98 0.81 94 1.09 92
0 vs. nutsedge *** *** ***
TD (30 to 120) Q*** Q*** Q**
ZValues were expressed as percent loss relative to those obtained with pepper grown
weed-free (0 TD).
NS, **, ***Main effects and interactions were nonsignificant or significant at P < 0.01 or
0.001, respectively, according to F tests. Competition (TD from 10 to 90) vs. no
competition (0 TD) effects were tested with contrasts. Effects of nutsedge density were
quadratic (Q) according to polynomial contrasts.









Table 1-4. Main effects of season, in-row bell pepper plant spacing, and initial yellow
nutsedge tuber density effects on large, marketable, and total pepper fruit weight in
spring and fall 2000.
Pepper fruit yield (t-ha' and % loss)
Large Marketable Total
Treatment t-ha' % loss' t-ha'" %loss t-ha"' %loss


Season (S)
Spring
Fall
Signif.
Pepper spacing
(PS; cm)
23
31
Signif.
SXPS
Tuber density
(TD; no'm"2)


21.38
2.55





13.66
12.37


**


63
91





74
78

*NS
NS


22.55
4.39





15.17
13.79
NS
NS


63
88





72
76

*NS
NS


24.71
4.96





16.67
15.19

*NS
NS


0 29.55 33.59 37.52
15 17.03 52 19.00 50 20.64 50
30 10.93 74 12.14 70 13.45 70
45 8.11 81 8.92 79 9.88 79
60 6.88 84 7.29 83 7.92 84
90 5.57 87 5.93 87 6.20 88
TD (15 to 90) C** Q*** C*
SXDEN "*** NS *** NS *** NS
ZValues were expressed as percent loss relative to those obtained with pepper grown
weed-free (0 TD).
NS. *, **. **Main effects and interactions were nonsignificant or significant at P < 0.05,
0.01, 0.001, respectively, according to F tests. Effects ofnutsedge density were
quadratic (Q) or cubic (C) according to polynomial contrasts.













90
1 0
S70
60-
'- 50-
540.
0-
c 30-
S20
S10
2 0


o Large: r2 = 0.71
* Marketable: r2 = 0.72
o Total: r2 =0.76


o Large: r2=0.70
* Marketable: r2 = 0.75
o Total: r2 =0.78


80
0 70



._ 40
.- 30
0
20- 0 Large: r2 =.41
2 10o- T Marketable: r2 = 0.49
v Total: r2 =0.55
0.

0 10 20 30 40 50 60 70 80 90 100 110 120

Initial nutsedae tuber density (no./m2)


Fig. 1-1. Main effect of initial yellow nutsedge tuber density on large,
marketable, or total bell pepper fruit weight in spring 1999, fall 1999, and in
2000 as percent loss relative to that with no nutsedge. Data in spring and fall
of 2000 were combined. Coefficients of determination (r2 values) were
determined by regressing data within means (shown).













Table 1-5. Coefficients for the rectangular hyperbola [Cousen's:
Y = ID/(l +ID/A)] used to characterize the effect of initial yellow
nutsedge tuber density on bell pepper fruit weights as percent loss
relative to those with no nutsedge.
Parameterz
Fruit grade I A
Spring 1999
Large 0.05 0.01 89.53 4.94
Marketable 0.04 0.01 90.82 5.24
Total 0.05 0.01 89.89 4.18
Fall 1999
Large 0.05 0.01 126.49 9.48
Marketable 0.04 0.01 126.32 10.10
Total 0.04 0.01 119.06 8.04
Spring and fall 2000
Large 0.08 0.02 102.76 6.19
Marketable 0.07 0.01 104.09 5.91
Total 0.06 0.01 104.60 5.28
ZCoefficients standard errors for each variable were obtained
with data within means.









Table 1-6. Main effects of in-row bell pepper plant spacing and initial yellow nutsedge
tuber density on pepper plant height during pepper flowering, fruit development, and
after final fruit harvest in spring 1999.
Pepper ht at three growth stages (cm)
Treatment Floweringz Fruit development Fruit harvest
Pepper spacing (cm)
22.9 25.0 51.2 53.2
30.5 25.0 52.0 54.5
Signif. NS NS NS
Tuber density (TD;
no..m-2)
0 22.4 47.9 49.9
30 23.4 51.4 53.1
60 25.6 53.3 55.8
90 26.7 54.2 56.3
120 26.8 51.3 54.1
0 vs. nutsedge *** ** **
TD (30 to 120) 0* NS NS
Tepper plant height from the bed surface to highest bud was measured during pepper
flowering, fruit development, and at fruit harvest at 6, 10, and 14 weeks after pepper
transplanting, respectively.
Ns. **, '*Main effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (30 to 120 TD) vs. no competition (0
TD) effects were tested with contrasts. The significant tuber density effect was
quadratic (Q) according to polynomial contrasts.









Table 1-7. Main effects of in-row bell pepper plant spacing and initial yellow nutsedge
tuber density on pepper plant height during pepper flowering, fruit development, and at
final fruit harvest in fall 1999.
Pepper ht at three growth stages (cm)
Treatment Floweringz Fruit development Fruit harvest
Pepper spacing (cm)
22.9 29.1 29.7 30.0
30.5 29.2 30.5 30.4
Signif. NS NS NS
Tuber density (TD;
no.-m'2)

0 31.4 33.0 32.0
10 32.7 33.9 33.6
20 31.2 31.9 31.3
30 30.8 30.9 31.6
60 24.7 25.8 26.2
90 24.2 25.3 26.3
0 vs. nutsedge X
TD (10 to 90) L*** L*** L***
ZPepper plant height from the bed surface to highest bud was measured during pepper
flowering, fruit development, and at fruit harvest at 6, 9, and 14 weeks after pepper
planting, respectively.
NS.X,. "**Main effects were nonsignificant or significant at P < 0.10, 0.05, or 0.001,
respectively, according to F tests. Competition (30 to 120 TD) vs. no competition (0
TD) effects were tested with contrasts. Significant tuber density effects were linear (L)
according to polynomial contrasts.









Table 1-8. Main effects of season, in-row bell pepper plant spacing, and initial
yellow nutsedge tuber density on pepper plant height during pepper flowering, fruit
development, and after final fruit harvest in spring and fall of 2000.

Pepper ht at three growth stages (cm)
Treatment Flowering' Fruit development Fruit harvest
Season


Spring
Fall


25.4
19.4


Signif.
Pepper spacing (cm)
22.9


30.5


23.0
22.4


44.8
23.4


35.1
35.4


49.4
26.6


38.9
39.6


Signif.
Tuber density (no.-m'2)
0
15
30
45
60
90
0 vs. nutsedge
Nutsedge (15 to 90)
Season X densityv


21.4
24.0
22.0
22.5
23.5
22.8


35.3
37.6
34.7
35.8
33.9
34.4


39.4
40.4
36.4
40.4
38.1
40.9


QR**
NS


ZPepper plant heights were obtained during flowering, fruit development, and after
fruit harvest 6, 10, and 14 weeks after pepper transplanting (WAT) in spring and 6,9,
and 14 WAT in fall, respectively.

'Interactions were determined with nutsedge treatments.
NS,**, '*Main effects and interactions were nonsignificant or significant at P < 0.01 or
0.001, respectively, according to F tests. Competition (15 to 90 TD) vs. no
competition (0 TD) effect at fruit harvest was tested with a contrast. Ttuber density
(15 to 90 TD) effect at fruit harvest was quartic (QR) according to a polynomial
contrast.
















Table 1-9. Interaction of season and initial yellow nutsedge tuber density on
pepper plant height during flowering and fruit development in 2000.
Tuber density (no.- m2)

Season 0 15 30 45 60 90 0 vs nutsedge Signif.z
Ht at flowering (cm)

Spring 23 24 25 26 27 27 *** L***
Fall 20 24 19 18 19 17 NS C*
Ht at fruit development (cm)

Spring 42 45 44 48 45 46 *** QR**
Fall 27 29 23 21 20 20 *L***
ZValues obtained with pepper grown weed-free (0) were excluded in tests for
significance of pepper height response to tuber density.
NS, *. ** Row effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001
according to F-tests. Competition (15 to 90 tubers-m2) vs no competition (0
tubersm'2r) effects were tested with contrasts. Significant tuber density (15 to 90
tubers-m-2) were linear (L), cubic (C), or quartic (QR) according to polynomial
contrasts.










Table 1-10. Main effects of in-row bell pepper plant spacing and initial
yellow nutsedge tuber density on leaf number per pepper plant during fruit
development and after final fruit harvest in spring 1999.
Leaves at two growth stages (no. and % loss)z
Fruit development Fruit harvest
Treatment no. % loss' no. % loss
Pepper spacing (cm)
22.9 69.4 62.7 62.9 52.7
30.5 72.0 69.5 69.9 58.5
Signif. NS NS NS
Tuber density (TD;
no.-m'2)
0 151.7 --- 122.5
30 61.3 58.8 64.3 44.7
60 56.9 62.3 57.1 51.1
90 42.1 71.2 44.1 63.6
120 41.5 72.1 44.3 63.0
0 vs. nutsedge *** ***
TD (30 to 120) L*** L*** L*** L**
ZPepper plants were sampled during fruit development and at fruit harvest
at 10 and 14 weeks after pepper transplanting, respectively.

"Values were expressed as percent loss relative to those obtained with 0
TD.
NS, *****Main effects were nonsignificant or significant at P < 0.05, 0.01,
or 0.001, respectively, according to F tests. Competition (30 to 120 TD)
vs. no competition (0 TD) effects were tested with contrasts. Tuber
density effects were linear (L) according to polynomial contrasts.









Table 1-11. Main effects of in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on leaf number per pepper plant during pepper flowering, fruit
development, and after final fruit harvest in fall 1999.
Leaves at three growth stages (no. and % loss)
Flowering Fruit development Fruit harvest
Treatment no. %loss' no. %loss no. %loss
Pepper spacing (cm)
22.9 26 52.8 26 46.0 25 47.4
30.5 28 51.8 29 47.2 28 50.9
Signif. NS NS NS NS NS NS
Tuber density (TD;
no.-m2)
0 49 --- 46 --- 45 ---
10 33 31.3 35 21.9 30 33.3
20 30 39.0 28 36.3 24 46.5
30 23 53.9 23 48.9 19 57.5
60 16 65.3 18 58.8 17 60.0
90 13 71.9 14 67.2 23 48.6
0 vs. nutsedge *** *** ***
TD (10 to 90) 0* Q* 0* 0* 0*** 0***
z Pepper plants were sampled during pepper flowering, fruit development, and at fruit
harvest at 6,9, and 13 weeks after pepper transplanting, respectively.
'Values were expressed as percent loss relative to those obtained with 0 TD.
NS, "*"*'Main effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (10 to 90 TD) vs. no competition (0
TD) effects were tested with contrasts. Tuber density effects were quadratic (Q)
according to polynomial contrasts.








Table 1-12. Main effects of season, in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on leaf number per pepper plant during late flowering, fruit
development, and at final fruit harvest in spring and fall 2000.
Leaves at three growth stages (no. and % loss)
Flowering' Fruit development Fruit harvest
Treatment no. %loss' no. %loss no. %loss
Season
Spring 39 28.7 67 64.8 52 59.6
Fall 16 41.3 21 63.1 21 62.0
Signif. *** NS *** NS *** NS
Pepper spacing (cm)
22.9 28 34.6 45 59.6 35 56.6
30.5 29 34.0 48 68.6 42 64.7
Signif. NS NS NS *** *** ***
Tuber density (TD;
no..m'2)

0 43 --- 103 --- 79 ---
15 35 14.3 56 43.6 42 47.3
30 29 25.8 40 60.1 32 59.2
45 25 38.8 31 69.2 29 61.7
60 23 42.8 27 72.4 23 69.0
90 19 49.9 24 75.0 25 66.9
0 vs. nutsedge *** *** ***
TD (15 to 90) Q* L*** Q*** Q*** Q*** Q***
ZPepper plants sampled during pepper flowering, fruit development, and after fruit
harvest at 6, 10, and 14 or 6, 9, and 14 weeks after pepper transplanting in spring and
fall, respectively
'Values were expressed as percent loss relative to those obtained with 0 TD.
NS, *' *' **Main effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (15 to 90 TD) vs no competition (0
TD) effects were tested with contrasts. Tuber density effects were linear (L) or
quadratic (Q) according to polynomial contrasts.


















o Fruit development r2 = 0.63
* Fruit harvest r2 = 0.37


o Flowering: r2 = 0.60
* Fruit development r2 = 0.51
0 Fruit harvest: ? = 0.36


S20 V' 1 0 Flowering: r2 0.23
-I 10 A Fruit development r2 0.59
0 0 Fruit harvest r2 =0.42

0 10 20 30 40 50 60 70 80 90 100 110 120
Initial nutsedge tuber density (no./m2)

Fig. 1-2. Main effect of initial yellow nutsedge tuber density on loss of leaf
number, relative to that with no nutsedge, in spring 1999, fall 1999, and in
2000. Data in spring and fall of 2000 were combined. Coefficients of
determination (r2 values) were determined by regressing data within means
(shown).















Table 1-13. Coefficients for the rectangular hyperbola [Y = A x X/(B +
X)] used to characterize the effect of initial yellow nutsedge tuber density
leaf number per pepper plant as percent loss relative to that with no
nutsedge.
Parameters
Pepper growth A B
Spring 1999
Fruit development 77.7 4.0 10.6 4.0
Fruit harvest 75.3 9.0 22.1 10.5
Fall 1999
Flowering 88.2 7.8 20.8 5.3
Fruit development 87.5 11.5 27.3 9.3
Fruit harvest --Y -
Spring and fall 2000
Flowering 91.2 32.7 70.0 45.3
Fruit development 89.6 4.1 15.0 2.6
Fruit harvest 75.4 3.3 8.6 2.0
ZCoefficients standard errors for each variable were obtained with data
within means. Models were significant at P < 0.001.

YThis equation was 168.5 90.0 x X/ (31.6 20.0 + X) 0.84 0.6 (X).
"x" = multiply sign









Table 1-14. Main effects of in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on leaf area per pepper plant during pepper flowering, fruit
development, and after final fruit harvest in spring 1999.
Leaf area at three growth stages (cm2 and % loss)
Flowering Fruit development Fruit harvest
Treatment cm2 % loss' cm2 % loss cm2 % loss
Pepper spacing (cm)
22.9 893 33.8 2043 61.4 1488 52.5
30.5 961 43.0 2141 68.1 1750 59.0
Signif. NS NS NS NS NS
Tuber density (TD;
no.-m2)
0 1356 --- 4392 --- 3006 --
30 1006 24.3 1761 59.2 1543 45.1
60 867 34.5 1737 60.0 1440 49.7
90 800 39.6 1205 71.7 1124 61.6
120 603 55.2 1369 68.2 982 66.7
0 vs. nutsedge *** *** --- ***
TD (30 to 120) L*** L*** C* L* L*** L**
ZPepper plants were sampled during pepper flowering, fruit development, and after
final fruit harvest at 6, 10, and 14 weeks after pepper planting, respectively.
'Values were expressed as percent loss relative to those obtained with 0 TD.
Ns', *, *****Main effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (30 to 120 TD) vs. no competition (0
TD) effects were tested with contrasts. Tuber density effects were linear (L) or cubic
(C) according to polynomial contrasts.








Table 1-15. Main effects of in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on leaf area per pepper plant during pepper flowering, fruit
development, and after fruit harvest in fall 1999.
Leaf area at three growth stages (cm2 and % loss)
Flowering Fruit development Fruit harvest
Treatment cm2 % loss' cm2 %loss cm2 %loss
Pepper spacing (cm)
22.9 532 51.1 527 41.4 518 45.3
30.5 555 43.8 551 43.9 543 49.0
Signif. NS NS NS NS NS NS
Tuber density (TD;
no..m-2)

0 914 --- 872 --- 902 ---
10 686 22.2 721 14.3 619 29.2
20 616 33.3 554 29.2 517 41.1
30 457 50.7 466 45.8 426 52.2
60 347 60.2 315 62.1 352 56.4
90 242 70.8 306 61.8 366 57.1
0 vs. nutsedge *** --- *** ***
TD (10 to 90) L*** L*** ** 0** 0** L**
zPepper plants were sampled during pepper flowering, fruit development, and after
fruit harvest at 6,9, and 14 weeks after pepper transplanting, respectively.
'Values were expressed as percent loss relative to those obtained with 0 TD.
Ns, *.** *** Main effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (10 to 90 TD) vs. no competition (0
TD) effects were tested with contrasts. Tuber density effects were linear (L) or
quadratic (Q) according to polynomial contrasts.









Table 1-16. Main effects of season, in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on leaf area per pepper plant during pepper flowering, fruit
development, and after final fruit harvest in spring and fall of 2000.

Leaf area at three growth stages (cm2 and % loss)
Flowering Fruit development Fruit harvest
Treatment cm2 %loss' cm2 %loss cm2 %loss
Season


Spring
Fall
Signif.
Pepper spacing (cm)
22.9
30.5
Signif.
Tuber density (TD;
no.'m2)

0
15
30
45
60
90
0 vs. nutsedge
TD (15 to 90)


630
219


444
451
NS



673
557
461
347
352
294


30.7
38.1


36.8
31.2
NS





10.7
25.0
41.8
42.5
49.8


1568
335


959


1081
*



2102
1238
864
710
644
563


60.2
64.2


60.1
63.9
NS





40.3
59.7
68.4
67.5
74.0


606


57.5
57.1


54.1
60.4


** NS


1324
751
562
494
412
413


39.4
54.9
60.4
65.4
66.3


Q***


ZLeaf area was recorded for pepper plants sampled during flowering, fruit
development, and after final fruit harvest at 6, 10, and 14 or 6, 9, and 14 weeks after
pepper transplanting in spring and fall, respectively.

'Values were expressed as percent loss relative to those obtained with 0 TD.
NS,, ,*** Main effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (15 to 90 TD) vs. no competition (0
TD) effects were tested with contrasts. Tuber density effects were linear (L), quadratic
(Q), or cubic (C) according to polynomial contrasts.



































0 Flowering: r2 = 0.41
* Fruit development: r2 = 0.36
o Fruit harvest: r2 = 0.27


0 Flowering: r2 = 0.18
A Fruit development r2 = 0.56
o Fruit harvest r2 = 0.33


0 10 20 30 40 50 60 70 80 90 100 110 120
Initial nutsedge tuber density (no./m2)

Fig. 1-3. Main effect of initial yellow nutsedge tuber density on loss of bell
pepper plant leaf area, relative to that with no nutsedge, in spring 1999, fall
1999, and in 2000. Data in spring and fall of 2000 were combined.
Coefficients of determination (r2 values) were determined by regressing data
within means (shown).












Table 1-17. Coefficients for the rectangular hyperbola [Y = A x
X/(B + X)] used to characterize the effect of initial yellow nutsedge
tuber density on leaf area per pepper plant as percent loss relative to
that with no nutsedge.
Parameters
Pepper growth stage A B
Spring 1999
Flowering 97.9 37.6 8.3 73.8
Fruit development 73.7 4.4 8.3 3.9
Fruit harvest 78.5 10.1 25.8 12.0
Fall 1999
Flowering 96.0 17.9 36.6 14.6
Fruit development 95.5 24.2 39.9 22.4
Fruit harvest 66.8 8.4 11.6 5.5
Spring and fall 2000
Flowering 98.5 49.6 80.1 69.7
Fruit development 88.2 4.6 16.0 3.0
Fruit harvest 78.8 5.9 14.0 4.1
ZCoefficients standard errors for each variable were obtained with
data within means. Models were significant at P < 0.001.









Table 1-18. Main effects of in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on leaf dry weight per pepper plant during pepper flowering,
fruit development, and after final fruit harvest in spring 1999.
Leaf dry wt at three growth stages (g and % loss)
Flowering Fruit development Fruit harvest
Treatment g % lossY g % loss g loss

Pepper spacing (cm)
22.9 4.30 37.86 10.14 61.12 8.83 52.95
30.5 4.67 46.77 10.72 66.16 10.66 57.55
Signif. NS NS NS NS NS
Tuber density (TD;
no..m2)

0 6.89 21.47 --- 18.01 --
30 4.99 26.55 8.83 58.04 8.64 48.20
60 4.06 39.51 8.81 58.84 8.95 47.77
90 3.80 42.92 6.07 70.76 6.79 61.16
120 2.70 60.27 7.00 66.92 6.33 63.88
0 vs. nutsedge *** *** ***
TD (30 to 120) L*** L*** C* L** L** L*
ZPepper plants were sampled during pepper flowering, fruit development, and after
final fruit harvest 6, 10, and 14 weeks after pepper planting.

'Values were expressed as percent loss relative to those obtained with 0 TD.
NS, *, ** **Main effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (30 to 120 TD) vs. no competition (0
TD) effects were tested with contrasts. Tuber density effects were linear (L) or cubic
(C) according to polynomial contrasts.








Table 1-19. Main effects of in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on leaf dry weight per pepper plant during pepper flowering,
fruit development, and after fruit harvest in fall 1999.
Leaf dry wt at three growth stages (g and % loss)
Flowering' Fruit development Fruit harvest
Treatment g %loss' g %loss g %loss
Pepper spacing (cm)
22.9 2.31 58.4 2.49 46.2 3.20 48.0
30.5 2.53 61.9 2.64 49.2 3.58 54.5
Signif. NS NS NS NS NS NS
Tuber density (TD;
no..m"2)
0 4.88 --- 4.43 --- 6.11 ---
10 3.18 33.5 3.48 18.2 3.98 33.1
20 2.50 49.3 2.56 35.9 3.39 43.2
30 1.81 62.9 2.13 50.9 2.67 55.2
60 1.30 72.4 1.37 67.6 2.14 61.0
90 0.85 82.6 1.41 65.8 2.07 63.7
0 vs. nutsedge *** --- ***
TD (10 to 90) 0* Q** Q** Q** Q** L***
zPepper plants were sampled during pepper flowering, fruit development, and after
fruit harvest 6, 9, and 13 weeks after pepper planting.
'Values were expressed as percent loss relative to those obtained with 0 TD.
Ns, *'***Main effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (10 to 90 TD) vs. no competition (0
TD) effects were tested with contrasts. Tuber density effects were linear (L) or
quadratic (Q) according to polynomial contrasts.









Table 1-20. Main effects of season, in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on leaf dry weight per pepper plant during bell pepper
flowering, fruit development, and after final fruit harvest in spring and fall 2000.
Leaf dry wt at three growth stages (g and % loss)
Flowering Fruit development Fruit harvest
Treatment g %loss' g %loss g %loss


Season
Spring
Fall


Signif.
Pepper spacing (cm)
22.9
30.5
Signif.
Tuber density (TD;
no.-m'2)


3.54
1.04



2.39
2.47
NS


34.0
50.6
X


43.8
38.9
NS


7.78
1.76



4.72
5.49
**


62.0
72.1
**


64.3
68.6
*


5.06
1.84



3.35
3.90
*


59.6
70.4
X


61.8
67.7
X


3.83
3.08
2.45
1.93
1.81
1.48


0 vs. nutsedge
TTM (1 A +t QA\


--- 11.02


16.5
30.1
47.5
52.0
60.7


6.18
4.24
3.47
3.04
2.67


7.90
45.0 3.91
64.2 2.86
71.4 2.69
74.5 2.17
77.3 2.24


47.6
64.1
66.9
72.0
71.6


zPepper plants were sampled during pepper flowering, fruit development, and after
final fruit harvest 6, 10, and 14 or 6, 9, and 14 weeks after pepper transplanting in
spring and fall, respectively

'Values were expressed as percent loss relative to those obtained with 0 TD.
NS, X, ,***,Main effects were nonsignificant or significant at P < 0.1, 0.05, 0.01, or
0.001, respectively, according to F tests. Competition (15 to 90 TD) vs. no
competition (0 TD) effects were tested with contrasts. Tuber density effects were
quadratic (Q) or cubic (C) according to polynomial contrasts.
















o^ 0


0 Flowering: r = 0.40
* Fruit development = 0.52
0 Fruit harvest: ? = 0.29


/ o Flowering: r2 = 0.61
/ A Fruit development r = 0.39
f/ 0 Fruit harvest: r2 = 0.36













SFlowering: r2 0.31
*/ Fruit development r2 = 0.64
So Fruit harvest: r2 = 0.39

0 10 20 30 40 50 60 70 80 90 100 110 120
Initial nutsedge tuber density (no./m2)


Fig. 1-4. Main effect of initial yellow nutsedge tuber density on leaf dry weight
per bell pepper plant in spring 1999, fall 1999, and in 2000 as percent loss
relative to that with no nutsedge. Data in spring and fall of 2000 were
combined. Coefficients of determination (r2 values) were determined by
regressing data within means (shown).


Rfl













Table 1-21. Coefficients for the rectangular hyperbola [Y = A x
X/(B + X)] used to characterize the effect of initial yellow nutsedge
tuber density on loss of bell pepper leaf dry weight.
Parameters
Pepper growth stage A B
Spring 1999
Flowering 100.8 33.5 95.0 59.4
Fruit development 72.6 4.4 8.42 4.0
Fruit harvest 70.4 8.9 17.0 10.1
Fall 1999
Flowering 98.9 8.5 19.2 4.7
Fruit development 94.8 18.6 30.9 14.9
Fruit harvest 73.3 7.6 12.2 4.6
Spring and fall 2000
Flowering 116.3 37.3 77.0 43.1
Fruit development 91.8 3.6 14.2 2.2
Fruit harvest 81.9 4.2 9.9 2.5
ZCoefficients standard errors for each variable were obtained with
data within means. Models were significant at P < 0.001.









Table 1-22. Main effects of in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on stem dry weight per pepper plant during pepper flowering,
fruit development, and after final fruit harvest in spring 1999.
Stem dry wt at three growth stages (g and % loss)
Flowering' Fruit development Fruit harvest
Treatment g %loss' g %loss g %loss
Pepper spacing (cm)
22.9 2.76 14.7 10.54 56.4 16.69 49.0
30.5 2.78 27.7 10.94 55.9 18.65 53.4
Signif. NS NS NS NS
Tuber density (TD;
no.'m2)

0 3.36 --- 19.65 --- 30.60 ---
30 3.10 7.4 9.02 53.6 15.45 47.0
60 2.66 20.3 9.90 49.3 16.64 43.9
90 2.62 20.8 7.26 61.7 13.43 55.1
120 2.12 36.3 7.88 60.0 12.26 58.9
0 vs. nutsedge *** --- *** ***
TD (30 to 120) L*** L*** C* C* L** L**
ZPepper plants were sampled during pepper flowering, fruit development, and after
final fruit harvest at 6, 10, and 14 weeks after pepper planting.

'Values were expressed as percent loss relative to those obtained with 0 TD.
Ns,*,****Effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (30 to 120 TD) vs. no competition (0
TD) effects were tested with contrasts. Tuber density effects were linear (L) or cubic
(C) according to polynomial contrasts.









Table 1-23. Main effects of in-row bell pepper plant spacing and initial yellow
nutsedge tuber density on stem dry weight per pepper plant during pepper flowering,
fruit development, and after fruit harvest in fall 1999.
Stem dry wt at three growth stages (g and % loss)
Flowering Fruit development Fruit harvest
Treatment g %loss' g %loss g %loss
Pepper spacing (cm)
22.9 2.34 60.2 3.00 45.8 3.70 57.9
30.5 2.50 62.7 3.18 51.7 4.01 64.0
Signif. NS NS NS NS NS NS
Tuber density (TD;
no.-m'2)
0 5.02 --- 5.38 --- 7.95 ---
10 3.27 33.4 4.19 18.9 4.73 39.5
20 2.37 52.4 3.15 37.8 3.59 54.6
30 1.83 63.3 2.61 49.6 2.82 64.6
60 1.26 74.2 1.61 68.8 2.02 72.3
90 0.80 83.9 1.60 68.4 2.00 73.7
0 vs. nutsedge *** --- *** --- ***
TD (10 to 90)( Q** 0* 0*** Q** 0** 0**
zPepper plants were sampled during pepper flowering, fruit development, and at fruit
harvest at 6, 9, and 13 weeks after pepper planting.
'Values were expressed as percent loss relative to those obtained with 0 TD.
NS, *,.**Effects were nonsignificant or significant at P < 0.05, 0.01, or 0.001,
respectively, according to F tests. Competition (TD from 10 to 90) vs. no competition
(0) effects were tested with contrasts. Tuber density effects were quadratic (Q)
according to polynomial contrasts.