Factors affecting the growth and production of minimum tillage peanuts

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Factors affecting the growth and production of minimum tillage peanuts
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Thesis (Ph. D.)--University of Florida, 1986.
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Bibliography: leaves 119-124.
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by Daniel Lamar Colvin.
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Vita.

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FACTORS AFFECTING THE GROWTH AND
.PRODUCTION OF MINIMUM TILLAGE PEANUTS









By

DANIEL LAMAR COLVIN


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


1986















ACKNOWLEDGEMENTS


I wish to express my sincere appreciation to Dr. Barry

Brecke, Dr. Wayne Currey, Dr. Fred Shokes, Dr. Ben Whitty,

and Dr. David Wright for their support and advice during the

course of this study and preparation of this manuscript.

Special thanks are extended to Dr. Barry Brecke, chairman of

my committee, and Dr. Wayne Currey, co-chairman of my

committee. Valuable advice, encouragement and intense

monetary support, without which this work could not have

been conducted nor completed, was provided by both these

members.

Thanks are extended to Dr. Donn Shilling, Dr. Dan

Gorbet, Dr. Tom Kucharek, Dr. Jerry Bennett, and Mr. Tim

Hewitt for their helpful suggestions and constructive

criticism during my research.

I am deeply grateful to Ms. Susan Durden for her

professional assistance in preparing this manuscript.

I would like to thank Raymond Robinson and Jimmy

Daniels for providing experimental sites in Williston and

Branford, Florida respectively. I am further grateful for

the donation of a Ro-Tills planter by Brown Manufacturing

Corporation and a twin 4-row planter unit by Vada

Manufacturing Corporation. I appreciate provisions made for









tractors and other equipment by Brookins Tractor

Corporation, Chiefland, Florida.

I thank my parents, Geral Daniel and Mary Claudette

Colvin, for their encouragement, love, and support

throughout the course of my education.

To my father and mother-in-law, William H. and Kathleen

S. McWhorter, whom I have come to love as my own parents, I

appreciate the encouragement and love given me during my

graduate education. I also thank them for giving me Suzy.

Finally, I owe most gratitude to my loving wife, Suzy.

Without any doubt, she is the best thing that has happened

to me throughout the course of my graduate education. Suzy

has stood by my side unshakeably, even during times when my

immature whims and childish outbursts should have driven her

away. If not for her, none of the ordeal I have endured to

obtain a higher degree would be worthwhile. Suzy deserves

this degree as much as I do, for I could not have made it

without her.


iii















TABLE OF CONTENTS


ACKNOWLEDGEMENTS ...................................

LIST OF TABLES .........................................

ABSTRACT ........ .............................. .......


Page

ii

vi

viii


CHAPTER 1.

CHAPTER 2.


CHAPTER 3.


CHAPTER 4.


CHAPTER 5.


CHAPTER 6.


INTRODUCTION ............................

VARIATIONS IN SURFACE AND SUBSURFACE
TILLAGE FOR PEANUT PRODUCTION ............

Introduction ............................
Materials and Methods .................
Results and Discussion ................

HERBICIDE SYSTEMS FOR MINIMUM TILLAGE
PEANUTS................. ..... ...... ......

Introduction ................... .........
Materials and Methods .................
Results and Discussion ................

WEED CONTROL, YIELD AND ECONOMIC ANALYSIS
OF FULL-SEASON DOUBLE-CROP PEANUTS GROWN
CONVENTIONALLY AND WITH MINIMUM TILLAGE....

Introduction ............................
Materials and Methods ..................
Results and Discussion .................

EFFECTS OF TILLAGE AND WHEAT STRAW
LEACHATES ON THE GERMINATION AND INCIDENCE
OF Sclerotium rolfsii IN PEANUTS ..........

Introduction ..........................
Materials and Methods ..................
Results and Discussion ..................

RESPONSE AND COMPARISONS OF EIGHT COMMON
PEANUT CULTIVARS PRODUCED CONVENTIONALLY
AND MINIMUM-TILLAGE ......................









Introduction ............................ 92
Materials and Methods ................. 101
Results and Discussion ........ ......... 103

CHAPTER 7. SUMMARY AND CONCLUSIONS ................... 113

LITERATURE CITED ...................................... 119

BIOGRAPHICAL SKETCH ............... .......... ........... 125









LIST OF TABLES


TABLE PAGE

2.1 Surface and subsurface tillage treatments.... 10

2.2 Peanut yield as affected by tillage system,
location, and year........................... 14

2.3 Force required to pull plants from the soil
as affected by tillage treatment............. 15

3.1 Minimum tillage peanut herbicide systems..... 26

3.2 Crop injury, cocklebur, sicklepod, Florida
beggarweed, and annual grass control ratings
as affected by herbicide systems in 1984..... 31

3.3 Crop injury, cocklebur, sicklepod, Florida
beggarweed, and annual grass control ratings
as affected by herbicide systems in 1985..... 33

3.4 Peanut yield as affected by herbicide
systems............................... ....... 39

4.1 Herbicide systems and treatment costs for
full-season double-crop, conventional and
minimum-tillage peanuts..................... 47

4.2 Peanut foliar injury as affected by herbicide
system (averaged across season and tillage).. 51

4.3 Annual grass control as affected by herbi-
cide system (averaged across season and
tillage) ......... .................... .... 53

4.4 Smallflower morningglory control as affected
by herbicide system (averaged across season
and tillage) ................................ 55

4.5 Sicklepod control as affected by herbicide
system (averaged across season and tillage).. 57

4.6 Florida beggarweed control as affected by
herbicide system (averaged across season
and tillage) ........................... ...... 58

4.7 Effect of season, tillage, and herbicide
system on peanut yield and net return at
Marianna, Florida 1984........................ 60

4.8 Effect of season, tillage, and herbicide
system on peanut yield and net return at
Jay, Florida 1985........................... 62









4.9 Effect of season, tillage, and herbicide
system on peanut yield and net return at
Williston, Florida 1985...................... 65

4.10 Herbicide system net returns as affected
by season and tillage (averaged across all
locations) ................................... 67

4.11 Effects of season of production on peanut
yield (averaged across tillage, herbicide
systems and locations)................... ..... 69

4.12 Effects of tillage on peanut yield (aver-
aged across season, herbicide systems and
locations) ........................ ........... 70

5.1 Stem rot hit counts as influenced by till-
age treatments...................... .......... 82

5.2 Peanut yield as affected by tillage treat-
ment...... ... ........... .. ............ ..... 85

5.3 Stem rot sclerotial germination as affected
by sclerotial age and wetting source......... 88

6.1 Effects of tillage on overall peanut yield
(averaged across all cultivars).............. 105

6.2 Effects of tillage on peanut yield by cult-
ivar and location............................ 107

6.3 Effects of tillage on overall peanut grade
characteristics (averaged across all cult-
ivars) ....................................... 109

6.4 Peanut grades by cultivar (averaged over
tillages) .................................... 111


vii















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



FACTORS AFFECTING THE GROWTH AND PRODUCTION
OF MINIMUM TILLAGE PEANUTS

By

Daniel Lamar Colvin

December, 1986



Chairman: Dr. B. J. Brecke
Cochairman: Dr. W. L. Currey
Major Department: Agronomy


Several factors that affect the production of

minimum-tillage peanuts were studied from 1984 to 1986 at

Branford, Gainesville, Jay, Marianna, Quincy, and Williston,

Florida. Included were studies of: 1) variations in

surface and subsurface tillage for peanut production (which

evaluated differences in no-tillage, minimum-tillage, and

conventional culture with or without subsoiling); 2) herbi-

cide systems for minimum-tillage peanuts (which evaluated

several weed control systems for possible use in

minimum-tillage peanuts); 3) weed control, yield and

economic analysis of full-season versus double-crop peanuts

grown either conventionally or minimum-tillage (which

evaluated the best season of production, best tillage

system, several herbicide systems and economic
viii








return to the grower); 4) effects of tillage and wheat straw

leachates on the germination and incidence of Sclerotium

rolfsii in peanuts (which examined no-tillage,

minimum-tillage, and conventional tillage effects on stem

rot of peanuts in the field, and the effects of wheat straw

leachates on S. rolfsii sclerotial germination) in the

laboratory; and 5) response and comparisons of eight common

peanut cultivars produced conventionally and minimum-tillage

(this study evaluated runner, Virginia, and Valencia

market-type peanuts for their suitability under

minimum-tillage as compared to conventional tillage.

Summarized results from all five studies indicate that

under Florida conditions minimum-tillage peanuts can be

produced successfully. Indications are that some form of

subsurface tillage (either subsoiling or subsurface

slitting) is needed for maximum yield. Successful herbicide

systems have been identified which perform well for

minimum-tillage peanut production. Full season production

was nearly always superior to double-crop. In addition, a

herbicide system of medium intensity performed best with

respect to economics and weed control whether used

with minimum or conventional tillage. Field studies show no

difference in the occurrence of stem rot in peanuts

regardless of the tillage system used; however, laboratory

studies show that sclerotia can be stimulated artificially

to germinate at a higher level when exposed to wheat straw








leachates. Finally, these studies indicate that runner,

Valencia and Virginia-market-type peanuts can be produced

successfully under minimum-tillage with few statistical

differences in yield as compared to conventional culture.













CHAPTER 1
INTRODUCTION



Peanuts (Arachis hypogaea L.) are an important cash

crop in the Southeast, especially in northern and central

Florida. For many years, peanuts have been produced with

intense tillage and seed bed preparation. These tillage

practices require many hours of field work with large

equipment utilizing large amounts of fuel. In addition,

intensive tillage and cropping practices on the sandy,

light-textured, infertile Florida soils can lead to

extensive erosion and loss of soil fertility.

Until recently, the profit margin offset the costs of

intensive tillage and land preparation for peanut

production. In recent years, peanut prices have not

increased as much as production costs. Consequently,

growers have become increasingly receptive to alternative

and more efficient methods of peanut production.

The use of minimum or conservation tillage farming is

becoming more popular in the United States. Minimum-tillage

offers many advantages compared to traditional agricultural

practices and provides solutions to many current soil and

crop management problems. It has become widely accepted for

crops such as corn (Zea mays L.), sorghum [Sorghum bicolor

(L.) Moench.], and soybeans [Glycine max (L.) Merr.].







2
However, little work has been done to evaluate

minimum-tillage for peanut production.

Five separate studies were established to examine some

of the crucial questions that must be answered in order to

successfully produce minimum-tillage peanuts. Experiment

One was designed to investigate variations in surface and

subsurface tillage and to determine the least amount of

tillage required to produce peanuts with yields equal to

those from conventional practices.

Experiment Two was established to identify potential

weed control systems for the production of minimum-tillage

peanuts. Traditionally weed control in peanuts has depended

to a large extent on volatile herbicides which must be soil

incorporated for weed control activity. It therefore

becomes extremely important to identify alternative

chemicals and approaches for successful minimum-tillage weed

control in a system where soil incorporation of herbicides

may not be possible.

The third study examined several economic factors

associated with the production of minimum-tillage peanuts

including planting dates (full season versus double-crop),

type of tillage (conventional versus minimum-tillage), and

intensity of weed control programs. Three intensities of

weed control programs were examined within combinations of

season and tillage.

Experiment Four was designed to investigate the

occurrence of Southern stem rot (Sclerotium rolfsii Sacc.),









a soilborne disease which was thought to have the potential

to be worse under minimum-tillage conditions. Direct

comparisons of conventional, no-tillage, and minimum-tillage

were made with respect to the occurrence of stem rot in

peanuts. An associated laboratory study was conducted to

investigate the effects of wheat straw leachates on disease

propagule germination. This study provided direct yield

comparisons between the three tillage types as well as

comparisons of disease occurrence.

Finally, experiment Five was implemented to ascertain

whether eight commonly grown peanut cultivars would perform

equally within comparisons of tillage type.

These experiments were designed to answer many

questions asked by growers and were carried out at several

locations in the peanut producing areas of Florida. This

work along with the work of several others provides a basis

on which to advise growers concerning the production of

minimum-tillage peanuts.















CHAPTER 2
VARIATIONS IN SURFACE AND SUBSURFACE TILLAGE FOR
PEANUT PRODUCTION


Introduction



The necessity to eliminate undesirable plants in

agronomic crops probably gave rise to soil tillage.

Throughout history, tillage has become accepted as a

necessary requirement for the production of most food crops.

In turn, many peanut producers and researchers alike believe

that tillage is necessary to reduce weed competition

(9,62) and disease incidence (6,7) and provide soil

conditions needed for favorable crop growth (63).

Traditionally, moldboard plowing has been done in late fall

to early winter to insure the decomposition of existing

plant residues. Although few data exist on the depth of

soil preparation in regard to peanut production, most soils

would be plowed 15 to 20 cm deep to allow for weed seed and

disease propagule burial. Conventionally prepared peanut

seed beds would normally be disked later in the season prior

to planting in order to further level the field and destroy

any weeds that were present. A final disking just before

planting would normally be used for incorporation of

preplant herbicides. This method of land preparation for






5

the production of peanuts has been termed "Deep Turning;

Non-Dirting" peanut culture by Boyle (6,7). This type of

land preparation procedure has been in use since the early

1950s and is practiced by most peanut producers in the

United States today. Prior research done by Garren (21),

Garren and Duke (22), and Mixon (41) shows significant

peanut yield increases when "Deep Turning; Non-Dirting"

culture was used as compared to lesser degree tillage

systems for peanut production.

In recent years, much research work has been devoted to

the minimum tillage (MT) production of many crops. Much of

this work has extolled benefits that may occur through

MT production of crops. Minimum tillage may offer several

advantages over present production systems such as 1)

reduced wind and water erosion, 2) reduced energy

requirements, 3) more flexible timing of planting and

harvesting, and 4) more efficient water utilization (49,62).

Additional research gives further advantages that may lead

to the adoption of MT practices. While copious amounts of

research can be found dealing with the MT production of corn

and soybeans, a survey of the literature reveals that only a

few researchers have investigated the MT production of

peanuts (14,15). Little or no data are available on the

effects of varying tillage from conventional practices to

lesser surface or subsurface tillage and trending toward

complete no-tillage production of peanuts.








Traffic or plow pans that exist in many southeastern

soils have made under-row subsoiling a popular tillage

method in both conventional and MT cultures of agronomic

crops. However, under-row subsoiling and other forms of

deep tillage require increased fuel costs and may slow

planting operations (18). With the introduction of a

slit-plant system by Elkins and Hendrick (17), the high

energy and draft requirements of subsurface tillage may be

reduced by as much as 40% over traditional under-row

subsoiling. Several new tillage methods have been

introduced since the work comparing gradations in disking to

moldboard plowing for the production of peanuts in the mid-

1950s (21,22,41).

Considering these factors, it was the objective of this

study to compare various surface and subsurface tillage

practices by examining root strength measurements and final

peanut yield.



Materials and Methods


Field experiments were conducted during 1984 in

Williston and Marianna, Florida, and during 1985 in

Williston and Jay, Florida. Soil types included a Zuber

loamy sand (Ultic Hapludalf) in Williston, a Chipola loamy

sand (Arenic Hapludult) in Marianna., and a Red Bay sandy

loam (Rhodic Paleudult) in Jay. The experimental design was

a randomized complete block with four replications. All









plots were seeded with the 'Sunrunner' (a runner type)

peanut cultivar at a seeding rate of 140 kg/ha. Row spacing

used was a twin 23 cm row pattern set on 76 cm row centers

with 53 cm wheel middles between sets of rows. The

experimental areas at all locations were seeded with wheat

(Triticum aestivum L.) in the fall prior to the initiation

of the experiments. All plots were sprayed with 1.12 kg

ai/ha of glyphosate approximately 2 weeks prior to peanut

planting to kill the wheat cover and existing weeds.

Herbicide treatments used in this experiment were

oryzalin + glyphosate 1.12 + 1.12 kg ai/ha (preemergence),

paraquat 0.14 kg ai/ha (ground cracking), and alachlor +

dinoseb + naptalam 3.36 + 1.12 + 2.24 kg ai/ha (early

postemergence). Experimental sites contained natural

infestations of Florida beggarweed [Desmodium tortuosum

(SW.) DC.], smooth crabgrass [Digitaria ischaemum (Schreb.)

Muhl.], and smallflower morningglory [Jacquemontia

tamnifolia (L.) Griseb.]. Soil fertilization and liming

practices were in accordance with soil test recommendations

of the University of Florida Soil Testing Laboratory.

In order to simulate wheat harvest and reduce stubble

height, the test area was mowed before planting allowing the

straw to scatter randomly over the plots. Strip-tilled

treatments were prepared using a modified Brown-Harden

Ro-tillo (Brown Manufacturing Co., Inc., Ozark, AL 36360)

planter with the actual planter units removed. The modified

Ro-till had of a short subsoiler shank with an attachable









slitter bar that penetrated the soil to a depth of

approximately 40 cm. Fluted coulters were mounted

on either side of the shank. The short subsoiler shank and

slitter blade combination opened the soil breaking up plow

pans beneath the row while fluted coulters smoothed the

ripped soil and broke up large clods. 'Rolling crumblers'

(barrel shaped devices that resemble a stalk cutter) were

mounted immediately behind the fluted coulters. Rolling

crumblers allowed further smoothing and shaping of the seed

bed. In addition, no-tillage treatments were prepared using

a KMC no-tillage planter with actual planter units removed.

The KMC planter employed a single long subsoiler shank (40

cm) directly beneath the row which performed similarly to

the Ro-Till system. Small rubber tires on each side of the

subsoiler shank pressed soil back into the subsoiler

channel. This system tilled an area approximately 6 cm wide

directly beneath the row with a minimum area of disturbed

soil compared to over 30 cm of disturbed soil prepared by

the Ro-Till system. Conventionally prepared treatments

were implemented with a moldboard plow set to run

approximately 20 cm deep with repeated diskings thereafter

to further smooth the seed bed. Tillage systems used are

shown in Table 2.1.

Planting was done in a separate operation due to

equipment limitations for small plot work. The twin-row

pattern was achieved by using a tool-bar-mounted twin-row

planter with the four planter units mounted 76 cm apart








center-to-center on the tool bar. Herbicides were applied

with a tractor-mounted, compressed air sprayer set to

deliver a diluent volume equivalent to 187 L/ha. Fungicide

and insecticide applications were made on an as-needed basis

throughout the season in accordance with accepted

recommendations.

Peanuts were planted in early May of 1984 and mid to

late May of 1985. They were dug in mid-September of both

years of the study. A conventional digger-shaker-inverter

was used to remove peanuts from the soil. Plots (1.5 x

7.7 M) were harvested with conventional equipment after

three days of field drying.

Data collected included final peanut pod yields

(adjusted to 7% moisture) and in two locations, root

strength measurements were made using a standard scale

mechanism and measuring force exerted (g/cm2) to pull plants

from the soil.

Root strength measurements and peanut yields were

subjected to analysis of variance and treatment means were

tested for differences using Duncan's multiple range test at

the 5% level of probability.









Table 2.1. Surface and subsurface tillage


TRT #


Surface
tillage


1 Strip tillagea
2 Strip tillage
3 Strip tillage
4 Strip tillage
5 No-tillagef
6 No-tillage
7 No-tillage
8 No-tillage


Sub-surface
tillage


Subsurface slitb
None
Subsurface slit


None
Subsoilingg
None
Subsoiling
None


Seed bed
condition


Stubble present
Stubble present
Conventional
Conventional
Stubble present
Stubble present
Conventional
Conventional


aStrip tillage--area approximately 30 cm tilled in row
center area with modified Brown-Harden Ro-till .

bSubsurface slit--Brown-Harden Ro-till fitted with
short subsoiler shank (24 cm) with 13 cm slitting bar
attached directly beneath to penetrate through plow pan.

CStubble present--upon final seed bed preparation for
planting wheat stubble is still present in plots except for
area directly in row.

None--no subsurface tillage.

eConventional--seed bed prepared through mold board
plowing and disking with either strip tillage or no-tillage
planter unit used at seeding.

fNo-tillage--area approximately 6 cm tilled directly in
row with all other area undisturbed, unless employed in
conventional plots.

Subsoiling--KMC No-tillage planter fitted with
subsoiler shanks penetrating approximately 36-40 cm into
soil profile. Chisel type point 5 cm in width.


treatments.









Results and Discussion



Germination and Growth of Peanuts

Peanuts germinated well in all treatments with a few

exceptions. Treatment 6 (no-tillage, no-subsoiling with

stubble present) experienced stand problems in varying

degrees at all locations. Stand problems were more severe

at locations with heavier soil types. In this treatment,

almost no soil preparation was done. As a result, the

twin-row planter often deposited seed directly on the soil

surface with little if any soil covering the seed. Seed

covering problems with this treatment led to somewhat poorer

stands in these plots. Final yields, however, did not seem

to be drastically affected by this problem. It is possible

that the plants present were able to compensate for the

missing plants. Generally, peanuts emerged more uniformly

in treatments which received moldboard plowing and

smoothing. Minimum tillage plots were always fully

germinated within one to two days of the conventionally

prepared plots. Although no actual data were taken on

seedling disease occurrence, no early season differences

were apparent with any treatment. Likewise, no differences

were noted between tillage treatments with respect to leaf

spot occurrence (Cercospora sp.) or stem rot (Sclerotium

rolfsii Sacc.). Although this test was not designed to

measure such occurrences, it does raise the question of

whether foliar and soilborne disease incidence can be









assumed to be no worse in MT peanut production than in

conventional culture. Other concurrent studies designed to

study the effect of tillage on soilborne diseases will be

discussed in subsequent chapters.



Weed Control Differences

Although the entire experimental area received the same

herbicide treatment, a few weed emergence by tillage

interactions were noted. Weed emergence seemed to be

correlated with the level of tillage performed. While this

factor was not experimentally measured, general plot

appearance revealed more uniform emergence of broadleaf

weeds in treatments receiving conventional preparations,

with herbicides appearing to be more efficacious on grasses

in these plots compared to MT plots. Fewer weeds emerged in

no-tillage plots than in the strip-tillage plots.

Grasses seemed to be more of a problem in the MT treatments

as compared to conventional treatments possibly due to the

fact that the broadleaf weed seed were never disturbed and

given the opportunity to germinate. The shallower grass

seed may have germinated due to interception of herbicide

material by wheat straw or other surface present organic

matter in no-tillage treatments. This phenomenon was not

observed when rain followed herbicide application within two

days.









Tillage treatment effects

The effect of variation in tillage treatments resulted

in significant location by year interactions. Tillage

effect will therefore be discussed by location and year of

study.

Marianna 1984. The 1984 growing season in Marianna was

very dry. As a result, yields across all treatments were

suppressed (Table 2.2). Due to the lack of moisture,

planting was delayed at this location. When peanuts were

planted, tillage equipment could not penetrate as deeply in

the soil as at other locations. In addition, there was no

irrigation available at this location making conditions even

worse.

Under these harsh growing conditions, few differences

in peanut growth and yield were found (Table 2.2). One

exception was in Treatment 3 (strip-tillage with a

subsurface slit over a conventionally prepared seed bed)

which yielded significantly better than other treatments.

The conventionally prepared seed bed allowed for good

lateral root development into a well prepared upper level

soil environment. In addition, the subsurface slit allowed

the plant tap root to penetrate the subsurface soil layers

to draw moisture and nutrients from greater depths in times

of drought. This treatment is superior to the comparable

treatment (Treatment 7) with a standard subsoiler chisel

foot. The larger channels of a subsoiler chisel tend to be

closed very quickly by subsequent machinery traffic and









Table 2.2. Peanut yield as affected by tillage system, location,
and year.


Locations and years


TRT#a Marianna Williston Jay Williston Williston
1984 1984 1985 1985A 1985B Avg.


----------------Peanut pod yield (kg/ha)b

1 2559 b 4162 ab 4279 ab 5002 a 4035 a 4007

2 2540 b 3702 b 4523 ab 3878 cd 4240 a 3779

3 3390 a 4943 a 5060 a 4513 abc 3781 a 4330

4 2061 b 4797 a 4397 ab 4709 ab 3898 a 3973

5 2686 b 4298 ab 4367 ab 3556 d 3546 a 3691

6 2237 b 3546 b 4201 b 4035 bcd 3917 a 3588

7 2442 b 4660 a 4826 ab 4357 abc 3781 a 4014

8 2090 b 4650 a 5022 a 4416 abc 4015 a 4047

aFor treatment description refer to Table 2.1.

bMeans followed by different letters within a column are
significantly different according to Duncan's multiple range
test (P = 0.05).









Table 2.3. Force required to pull plants from the soil
as affected by tillage treatment.


Location and years


TRT#a Williston 1984 Williston 1985A

2 ^b
--(g/cm2 root resistance) -

1 12.27 ab 12.95 ab
2 12.58 ab 10.62 ab
3 17.55 a 12.22 ab
4 12.83 ab 9.65 b
5 14.60 ab 14.98 a
6 10.68 b 13.35 ab
7 11.98 ab 14.18 ab
8 15.98 ab 13.40 ab


aFor treatment description, refer to Table 2.1.

bMeans followed by different letters within a
column are significantly different according to Duncan's
multiple range test (P = 0.05)









plants can utilize the opened channel for only a short time

after planting. Elkins, Thurlow and Hendrick (18) have

pointed out that many times the wider chisel subsoiler feet

will cause undesirable surface and subsurface soil mixing

which can be detrimental to plant root growth. No other

significant differences were noted among tillage treatments

at the Marianna location in 1984.

Williston 1984. At the Williston location, treatments

receiving conventional tillage either with or without any

subsurface tillage were superior to other treatments (Table

2.2). Treatments 3,4,7 and 8 were significantly better than

treatments 2 and 6 (Table 2.2). Treatments 2 and 6 received

no form of subsurface tillage and only minimal surface

tillage. Treatments 1 and 5 were minimum tillage treatments

as well but each of these treatments received subsurface

tillage either as a slit (Treatment 1) or subsoiler chisel

(Treatment 5). With only a small surface area tilled,

plots receiving treatments 2 and 6 apparently developed a

"lazy root system". Roots grew near the soil surface and

did not seem to branch out much into the subsoil as was

indicated by the force required to pull plants from the soil

(Table 2.3). Peanuts receiving treatments 1 and 5 did not

develop a surface root system but were able to penetrate the

subsoil to gain added moisture and nutrients (Table 2.3).

While treatments 3,4,7 and 8 yielded the greatest

numerically, systems 1 and 5 were not significantly

different in yield from the four best treatments.









Jay 1985. The soil type at Jay was the heaviest of all

the locations in the study. Soil type here was a Red Bay

sandy loam with enough clay to almost be considered a sandy

clay loam. Fewer tillage differences were seen on the

heavier soil. Treatments 3 and 8 yielded numerically the

highest but not significantly higher than the majority of

other treatments (Table 2.2). These two treatments

probably yielded higher than treatment 6 (no surface or

subsurface tillage with stubble present) due to reasons

pointed out earlier. Interestingly enough, system 3 which

received subsurface slitting, and treatment 8 which received

no subsurface tillage were statistically equivalent in

peanut yield. Several factors could have prevented yield

differences from developing. First, this soil type was not

nearly as sandy as in the other locations and the layer of

clay accumulation was closer to the soil surface.

Therefore, this soil had a better water-holding capacity and

did not tend to form soil hard pans as readily as sandier

soils underlain by a deeper clay layer. In addition, soil

moisture at Jay in 1985 was adequate due to ample rainfall

and supplemental irrigation. Once again, the "lazy root

syndrome" was evidenced in treatment 6 which had minimum

surface tillage and no subsurface tillage.

Apparently with adequate moisture and heavier soil,

subsurface tillage may be of little importance as long as

the surface is friable. This observation tends to agree

with popular belief among growers and equipment









manufacturers that few benefits from any type subsurface

tillage will be reflected in increased yields on many

heavier midwestern soils (Personal communication, Rick

Brown, Brown Manufacturing Co., Inc., Ozark, AL 36360;

Personal communication, David Bird, Bushhog Manufacturing

Corp., Selma, AL 36701).

Williston 1985A. This study was established in

Williston in 1985 at two different locations. 'Williston

location A was established in an area which had been

previously cropped with peanuts and soybeans but was not

back in the identical plots of 1984. Yield data from plots

receiving treatment 1 (strip tillage, subsurface slit with

stubble present) had the highest numerical yields. Yields

from plots receiving treatments 3,4,7,8, all with some

degree of conventional tillage, were statistically

equivalent (Table 2.2). Lower yielding treatments (2,5,6)

did not have any form of subsurface tillage with the

exception of treatment 5. It is possible that treatment 5

results were poor due to planter and stand problems

experienced with this particular system. By mid-season,

plants had filled in skips and a full canopy was

established. Root strength measurements (Table 2.3) show

this treatment to have the highest root strength possibly

due to less plant to plant competition for light, water, and

nutrients which allowed these plants to produce better root

systems. However, plants in this treatment were unable to

produce as many mature nuts as more optimally spaced plants









in other treatments. Few other significant trends can be

evidenced from yield or root strength data between

treatments.

Williston 1985B. The second Williston location in 1985

was established in an area which had previously been a

bahiagrass (Paspalum notatum Flugge) pasture for 8 years.

Yield data showed no differences between tillage treatments

(Table 2.2). This is supported by many years of grower

experiences showing that peanuts following bahiagrass will

consistently yield much better than any other rotational

crop (Personal communication, Dr. E.B. Whitty, University of

Florida Extension Peanut Specialist, Gainesville, FL 32611;

Personal communication, Mr. Dallas Hartzog, Peanut

Agronomist, Headland, AL 36330). Bahiagrass roots tend to

open up many macro and micro pores into the soil profile up

to depths of 1 M (17,52). This condition will allow future

crop roots to grow unimpeded. Optimum conditions for peanut

root growth had already been established throughout the

experimental area and no yield differences were detected

regardless of the tillage system imposed.

Overall Conclusions

Data collected from all test sites indicated that there

is no substitute for a good friable seed bed for maximum

peanut growth and yield. Plots that received some degree of

conventional surface tillage consistently had higher yields

than treatments where little, if any, surface tillage was

applied. Apparently some surface tillage is important for









maximum yield production of peanuts. Subsurface tillage is

very important especially in extremely dry years and is

probably needed most on lighter soils underlain by hard pans

in which water holding capacity is low. This research tends

to corroborate the findings of Elkins, Thurlow, and Hendrick

(18) in that the slit tillage system provided equal to

superior yields over standard chisel point subsoiling

techniques. However, it should be pointed out that

substantial problems were encountered with slitter wear and

breakage in rocky soils. It is believed that these

drawbacks may be overcome with proper materials and

engineering.















CHAPTER 3
HERBICIDE SYSTEMS FOR MINIMUM-TILLAGE PEANUTS





Introduction



Seed bed preparation through conventional tillage

methods has traditionally eliminated existing weeds and

allowed for good seed-soil contact. Obtaining satisfactory

weed control with minimum and no-tillage crop production

systems where mechanical cultivation may be no longer

possible has been the major concern of many producers (31).

In many minimum tillage (MT) operations a general change in

weed control programs is necessary since herbicides

requiring soil incorporation will be difficult if not

impossible to utilize with most MT planting equipment. It

is necessary, therefore, to identify weed control programs

which provide adequate weed control in minimum tillage

production.

Many researchers have studied weed control systems used

with minimum tillage in the corn belt (38,68,70) and have

expressed the need to increase weed control research in

these systems due to continued grower acceptance of MT (69).

Early work with weed control in no-tillage corn by Harold et

al. (26) pointed out that when tillage is eliminated,









satisfactory herbicide performance becomes imperative. They

also recognized the need for more than one herbicide in

no-tillage production and encouraged early killing of the

sod and/or existing weeds before planting.

Sanford et al. (59) found that poor weed control was

the greatest problem encountered with no-tillage double-crop

soybean and grain sorghum production. Weed species shifts

have been observed in several no-tillage crops as well,

often resulting in greater problems with annual grasses,

vine weeds, and perennial weeds (2,68). Robison and Wittmus

(55) compared several herbicide "system approaches" applied

to disked and no-tillage plots planted with corn and sorghum

and found that weed control was better on disked than

non-disked ground. They suggested that herbicide

interception by the crop residue was responsible for this

differential. Erbach and Lovely (19), by contrast, did not

observe any significant weed control reduction when applying

several herbicides to field plots containing up to 4,000

kg/ha of plant residue. Kincade (32) suggests that

effective weed control in no-tillage soybeans can only be

achieved through the use of several herbicide combinations.

He found that even when using a combination of herbicides,

johnsongrass [Sorghum halepense (L.) Pers.] populations

still increased in no-tillage production and suggested that

no-tillage soybeans should not be grown in johnsongrass

infested fields. Chappel (11) found that glyphosate was

more effective than paraquat in controlling emerged









perennial weeds but both were equally effective in

controlling emerged annual weeds. Triplett (66), however,

states that both glyphosate and paraquat were satisfactory

as herbicides used to control existing vegetation. The

general consensus of many researchers is that a successful

weed control program in minimum tillage must include a

contact burn down material applied at planting, a residual

material applied preemergence, and at times a selective post

emergent herbicide (26,31,54,66,68).

Researchers have agreed on several weed control

principles relating to minimum tillage. Among these are the

following: 1) In no-plow tillage systems, weed seeds tend

to accumulate near the soil surface putting somewhat greater

pressure on herbicides used; 2) Surface residue may possibly

intercept and render unavailable a portion of preemergence

herbicides; 3) A dense soil surface mulch with moisture

held in from this cover is an excellent germination medium

for weed seeds; 4) Perennial weed species, both herbaceous

and woody may increase with minimum tillage; 5) Herbicide

systems are more successful than a single preemergence

application in minimum-tillage systems; and 6) Early

germinating weed species can become dominant if control is

not adequate at planting time. These principles may make

weed control the most limiting (but not insurmountable)

aspect of minimum tillage production of crops.

No articles were found that deal with weed control

systems for MT peanuts exclusively. Colvin et al. (14)









examined cultivars, row spacing, and limited weed control

systems for peanuts and identified one or two possible

choices for production. However, MT peanut production is

occurring in the peanut producing region of several states

with both successful and unsuccessful attempts. Most

unsuccessful attempts have been directly related to weed

control problems.

With so little research available in MT peanut

production, there is a need to expand our knowledge of MT

weed control systems for peanuts. Expanded knowledge of

herbicide systems for MT peanuts was a major objective of

this study. A second objective was to find possible methods

which allow soil incorporation of dependable weed control

chemicals for MT production.



Materials and Methods



Field experiments were conducted during 1984 and 1985

in Williston, Florida on a Zuber loamy sand (Ultic

Hapludalf). The experimental design was a randomized

complete block using the 'Sunrunner' peanut cultivar (a

runner-type peanut) at a seeding rate of 140 kg/ha. Row

spacing used was a twin 23 cm row pattern set on 76 cm row

centers with 53 cm wheel middles between sets of rows. The

experimental area had most recently been in corn (Zea mays

L.) and soybean [Glycine max (L.) Merr.] production and was

seeded with wheat (Triticum aestivum L.) in the fall prior









to initiation of the experiments. All plots were sprayed

with 1.68 kg/ai/ha of glyphosate approximately 2 weeks prior

to peanut planting to kill the wheat cover and existing

weeds.

Herbicide systems investigated are listed in Table 3.1.

The experimental site was infested with common cocklebur

(Xanthium strumarium L.), sicklepod (Cassia obtusifolia L.),

Florida beggarweed [Desmodium tortuosum (SW.) DC.],

goosegrass [Eleusiue indica (L.) Gaertn.], and crowfoot-

grass [Dactyloctenium aegyptium (L.) Richter]. Soil

fertilization and liming practices were in accordance with

soil test recommendations of the University of Florida Soil

Testing Laboratory.

In order to simulate wheat harvest and reduce stubble

height, the test area was mowed before planting allowing the

straw to scatter randomly over the plots. Minimum-tillage

planting strips (40 cm wide) were prepared using a Brown-

Harden Ro-Till" planter, with the actual planter units

removed. The Ro-Till consists of a subsoiler shank that

penetrates the soil to a depth of approximately 36 cm.

Fluted coulters were mounted on either side of the shank.

The subsoiler shank opens the soil and destroys plow pans

beneath the row, and the fluted coulters smooth the ripped

soil and dissipate large clods. 'Rolling crumblers'

(barrel-shaped devices that resemble a stalk cutter) were

mounted immediately behind the fluted coulters. The rolling

crumblers served to further smooth and shape the seed bed.









'able 3.1. Minimum tillage peanut herbicide systems.

Rates and times of


'RT #


PPIRa


PREb


ACC


----------------------- kg/ai/ha -------------------------


8 pendimethalin 1.12


oryzalin

oryzalin


pendimethalin


ethafluralin





metolachlor
prometryn
pendimethalin
cyanazine


pendimethalin 1.12
benefin 1.68


1 benefit
vernolate
2 ethafluralin


1.68
2.26
1.68


3 benefin 1.68
vernolate 2.26
4 benefin 1.8
5 WEEDY CHECK
6 HAND WEEDED CHECK


1.12 paraquat

1.12 alachlor
dinoseb
naptalamn
1.12 alachlor
dinoseb
naptalam
1.68 ethafluralin
dinoseb
naptalam
alachlor
dinoseb
naptalam
2.26
2.26
1.12
2.26
alachlor
dinoseb
naptalam
dinoseb
alachor
dinoseb
naptalam
dinoseb


dinoseb
ethafluralin
dinoseb


prometryn


2.26


Entire experimental a
g/ai/ha prior to planting.


rea received glyphosate at 1.68


aPPIR Preplant incorporated within a 40 cm band by rolling
baskets centered on the row drill.

PRE designates surface herbicide application
,reemergence to crop and weeds.
AC designates treatment applied 15 to 20 days after
planting.


0.28

3.36
1.68
3.36
3.36
1.68
3.36
1.68
1.68
3.36
3.36
1.68
3.36




3.36
1.68
3.36
1.68
3.36
1.68
3.36
1.68

1.68
1.68
1.68











application of herbicides

Postemergence
EPd EPDSe Mpf LP9

--------------------------- kg/ai/ha ---------------

dinoseb 1.12 -- --
naptalam 2.26
dinoseb 0.84 -- --


dinoseb 0.84 --- -- -


dinoseb 0.84 ---


dinoseb 0.84 ---- -- dinoseb 0.84


-- -- paraquat 0.28

dinoseb 0.84 ---- ---- dinoseb 0.84

dinoseb 0.84 --


--~- paraquat 0.28 ---
2,4-DB 0.28


---- cyanazine 1.68 --

---- paraquat 0.28 -- --

S--- -- cyanazine 1.68

--- paraquat 0.28 ---




dEP designates herbicide application over the top of crop
and weeds applied 30 to 40 days after planting.
eEPDS designates herbicide application directed away from
crop plants and into row middle over applied 30 to 40 days after
planting.

MP designates herbicide application over the top of crop
and weeds applied 40 to 50 days after planting.

gLP designates herbicide application over the top of crop
^ .3---a .... --3 1 <^ -. .-r









Preplant incorporated in-row (PPIR) (Table 3.1) spray

applications were made with a nozzle system attached

directly behind the fluted coulters and in front of the

rolling crumblers (Table 3.1). Spray material was actually

pleated into the soil lifted by the fluted coulters and then

mixed thoroughly by the rolling basket action. Fluorescent

dye comparisons show crumbler incorporation to be equal to

one pass with a lightweight finishing disk (Personal

communication, Dr. John Everest, Extension Weed Specialist,

Auburn University, AL. 36849).

Planting was a separate operation due to equipment

limitations. The twin-row pattern was achieved by using a

tool-bar-mounted twin-row planter with the four planter

units situated 76 cm apart center-to-center on the tool bar.

Preplant incorporated, preemergence, at-cracking, and

postemergence over-the-top herbicide applications were made

with a tractor-mounted, compressed air sprayer set to

deliver 187 L/ha. Postemergence directed sprays were made

with a single nozzle boom and CO2 back pack sprayer that

also delivered 187 L/ha. Granular herbicide treatments were

applied by hand to individual plots using a shaker can.

Fungicide and insecticide applications were made on an

as-needed basis throughout the season in accordance with

accepted recommendations.

Peanuts were planted in early May of 1984 and mid-May

of 1985 and were dug in mid-September of both years of the

study. A conventional digger-shaker-inverter was used to









remove peanuts from the soil. Plots (1.5 x 7.7 M) were

harvested with conventional equipment after three days of

field drying.

Data collected included early-, mid-, and late-season

weed control ratings. Weed control ratings were made based

on percent controlled compared to the check; e.g., 100 to

90%--excellent control, 90 to 80%--good control, 80 to 70%--

fair control, and below 70%--unacceptable control. Peanut

yields were adjusted to 7% moisture.

Weed control ratings and yield data were subjected to

analysis of variance and treatment means were tested for

differences using the Least Significant Difference (LSD)

test at the 5% level of probability.



Results and Discussion



General Trends

The overall objective of this study was to investigate

prospective herbicide systems for minimum tillage peanut

production. In keeping with this objective, all systems

were designed to produce good weed control knowing in

advance the approximate natural weed population. As a

result, many of the fourteen herbicide systems worked quite

well on the species present in the study. This makes it

difficult to identify one system (Table 3.1) as superior to

another but does demonstrate the wide scope of weed control

alternatives provided by using a herbicide systems approach.









A concurrent objective of this study was to evaluate

possible means of incorporation of traditional preplant

peanut herbicides which must be mixed in the soil in order

to avoid loss of herbicidal activity through volatalization.

Treatments 8 through 14 all received herbicides incorporated

in the row area by the rolling basket arrangement (described

in Materials and Methods section). Weed control ratings

(Table 3.2 and 3.3) show these treatments to be as effective

as traditional preemergence applied minimum-tillage

herbicides. An evaluation of herbicide system costs would

show these treatments (8-14) to be more favorable since the

row area (40 cm wide strip) is the only area treated with a

herbicide at planting. Therefore, two-thirds less herbicide

material would be used at planting time possibly

representing a significant savings to the grower. In

addition, incorporation of herbicides within the row area

allows a certain degree of weatherproofing in the minimum

tillage system.

Traditionally, one of the serious complaints with

minimum-tillage weed control has been vulnerability due to

total dependence upon herbicides which require rainfall for

activation. If there is no rain, farmers could still use

post directed sprays to rescue a crop from a serious weed

problem in row middles. The questions of what to do with

escaped weeds in the row drill needs further investigation.

Weed Control and Crop Injury Ratings

Because there were significant treatment differences









Table 3.2. Crop injury, cocklebur, sicklepod, Florida
beggarweed, and annual grass control ratings as affected
by herbicide systems in 1984.

Weed Controla


Trt. No.b



1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

LSD


Crop Injury Cocklebur

--------------Time of Ratingc-------------

Early Mid Late Early Mid Late

----- --------------------


19

13

22

13

19

20

17

22

17

14

9

10

6

22

0

0

10.3


0

0

4

0

0

0

3

0

0

0

0

5

0

0

0

0

4.7


99

96

94

92

91

99

95

93

99

96

96

97

66

96

0

100

6.6


93

84

83

81

84

94

92

80

87

85

97

87

90

93

0

100

11.4


80

56

75

55

67

87

84

58

70

76

82

54

86

67

0

100

27.6


aMeans within a column can be statistically compared
using LSD (P=0.05) value located in bottom row adjacent to
each column.
bFor weed control treatments refer to Table 3.1.












Weed Controla


Sicklepod Fla. Beggarweed Annual Grassesd

----------------------Time of Ratingc--------------

Early Mid Late Early Mid Late Early Mid Late

-------------------------- % -------------------------

93 83 71 94 92 64 100 97 86

96 87 79 99 96 80 100 99 88

93 82 76 100 92 65 99 89 90

86 77 62 93 80 65 100 100 90

93 92 80 95 91 75 78 68 38

99 94 85 99 94 73 100 100 93

80 72 45 97 89 81 99 92 88

96 94 78 98 89 79 93 87 73

98 94 80 98 92 79 100 89 83

94 95 82 97 90 74 97 81 70

96 89 70 99 89 65 90 92 89

99 94 80 99 96 70 100 100 91

79 81 79 75 84 72 57 63 51

96 96 80 99 90 72 96 80 65

0 0 0 0 0 0 0 0 0

100 100 100 100 100 100 100 100 100

7.3 11.2 18.9 7.6 7.1 13.9 9.8 11.5 26.5


CEarly--30 days after planting, Mid--70 days after planting,
Late--120 days after planting.

Annual grass consisted of 60% goose grass and 40% crowfoot-
grass.









Table 3.3 Crop injury, cocklebur, sicklepod, Florida beggarweed,
and annual grass control ratings as affected by herbicide systems
in 1985.

Weed Controla


Treatment No.


1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

LSD


Crop Injury Cocklebur

--------------Time of Ratingc

Early Mid Late Early Mid Late

------------- % --------------


18

7

0

0

0

4

9

8

3

0

0

1

0

0

0

0

6.4


0

0

0

0

9

0

10

0

0

0

0

0

0

25

0

0

18.2


100

100

100

100

100

100

100

100

100

100

100

100

100

100

0

100

0


98

100

100

100

100

100

100

100

100

100

100

100

100

100

0

100

.89


93

100

98

95

95

92

92

92

91

90

95

92

95

95

0

100

5.4


aMeans within a column can be statistically compared using LSD
(P=0.05) value located in bottom row adjacent to each column.

bFor weed control treatments refer to Table 3.1.












Weed Controla


Sicklepod Fla. Beggarweed Annual Grassesd

------------------------Time of Ratingc--- ---------------

Early Mid Late Early Mid Late Early Mid Late

------------------------ ------------------------------

91 87 80 91 86 81 100 100 95

98 96 90 99 97 95 96 98 98

100 98 92 97 95 92 100 100 98

89 86 86 96 91 88 100 100. 97

93 94 84 93 89 76 93 92 92

90 82 85 90 81 79 94 95 88

85 84 76 92 88 84 100 100 96

94 92 84 95 81 74 100 99 92

87 87 82 89 75 70 100 100 95

100 97 79 91 84 65 100 100 92

90 90 83 90 87 79 94 95 90

89 82 77 96 93 84 100 100 95

89 77 77 77 94 91 95 98 96

87 84 84 85 57 59 96 91 90

0 0 0 0 0 0 0 0 0

100 100 100 100 100 100 100 100 100

8.9 11.8 8.8 8.5 15.8 18.6 6.6 6.7 7.5

CEarly--30 days after planting, Mid--70 days after
planting, Late--120 days after planting.
dAnnual grass consisted of 60% goose grass and 40%
crowfootgrass.








from 1984 to 1985 in crop injury, weed control and peanut

yields, this data will be discussed separately by year.

Early (approximately 30 days after planting), mid (70 days

after planting), and late (120 days after planting) season

weed control ratings were made.



Crop injury. 1984 growing conditions were much harsher

than 1985. Peanuts were irrigated shortly after planting to

activate herbicides. No significant rainfall occurred for

40 days thereafter in 1984. Early season crop injury

ratings from 1984 reveal that several of the treatments

caused injury in excess of 15% (Table 3.2). This may have

been due to the unusually dry weather conditions which

prevailed up to this rating period. By the time of the Mid

and late season ratings, only the treatments receiving

dinoseb or paraquat postemergence exhibited substantial crop

injury.

During 1985 conditions early in the season were much

better with natural rainfall patterns near normal for the

experimental area. Visual ratings (Table 3.3) show only

minimal early season crop injury with most of the peanuts

recovering by the mid-season rating. Once again in 1985

those treatments that received dinoseb or paraquat over the

top still showed injury at the mid-season rating. By late

season, however, all visual injury had dissipated.

Cocklebur control. Cocklebur control was generally

less in 1984 (Table 3.2) than in 1985 (Table 3.3) for all









herbicide systems evaluated. This again is due in part to

rainfall patterns in 1984 that resulted in less than

adequate herbicide activation and subsequently poor weed

control. The dry weather conditions also resulted in poor

crop growth and affected the ability of the crop to compete

with the cocklebur. In addition, the experimental site was

shifted in 1985 for crop rotational reasons and the

experiment was located in an area where the cocklebur

population was much less severe than in the 1984 area.

Early and mid-season 1984 ratings (Table 3.2) show fairly

good control from most systems. Late season ratings,

however, began to evidence the fact that herbicides used in

many of the systems were dissipating with numerous cocklebur

present in most systems by 120 days after planting.

Meanwhile, 1985 data (Table 3.3) show cocklebur control to

be excellent both at early and mid-season ratings due to

adequate rainfall patterns and due to the fact that the

overall cocklebur population was approximately 7 fold lower

at the 1985 site when compared to the 1984 experimental

site. While some control reduction was noted by the late

season rating, most systems maintained control above 90%

throughout the 1985 season.

Sicklepod control. Sicklepod control closely mirrored

cocklebur control with many of the same trends evidenced.

Overall, sicklepod control seemed to be a little better in

1985 than in 1984 due to reasons previously mentioned.

Sicklepod control ratings do, however, identify some systems









which were weak at the early period of rating in 1984 (i.e.

systems 7 and 13) (Table 3.2). Control in these systems did

not improve throughout the season. These two systems as

well as several other systems exhibited unacceptable season

long control (Table 3.2). The 1985 ratings show better

control early and mid-season; however, by late season,

several herbicide systems had fallen to only fair control of

sicklepod (Table 3.3).

Florida beggarweed control. Florida beggarweed is a

serious peanut weed pest which usually does not germinate

until later in the growing season when soil temperatures

are higher. Due to the germination pattern of this weed, a

special problem is encountered in its control. Many times

Florida beggarweed will not germinate until 30 to 45 days

after peanut planting when much of the soil activity from

previously applied herbicides has diminished. Weed control

ratings in 1984 (Table 3.2) reflect this trend. Early

season control from all systems was quite good since little

or no beggarweed had begun to germinate. By the mid-season

rating, however, several systems began to exhibit diminished

control and by late season, only two systems (2 and 17)

still exhibited good control of Florida beggarweed.

Similar trends in Florida beggarweed control were

observed in 1985. Most treatments exhibited good early

season control with poorer control later in the season

(Table 3.3). Overall, however, control of this weed was

better in 1985 compared to 1984 due to timely rainfall and









good herbicide activation as well as reduced weed pressure

in the 1985 experimental area.

Annual grass control. The experimental areas in 1984

and 1985 were infested with a mixture of crowfootgrass and

goosegrass. Distribution at both locations was

approximately 60% goosegrass and 40% crowfootgrass. Annual

grass control reflects many of the same seasonal control

trends as did the annual broadleaf species. In 1984 (Table

3.2), excellent to good control was obtained both at early

and mid-season. However, by late season, grasses had begun

to invade many of the plots and some were completely over

run by grasses. Better overall control of grasses was

obtained in 1985 by all systems. Late season ratings

indicate that many of the systems gave good to excellent

control up to 120 days after planting. These ratings again

highlight the importance of favorable weather conditions

during early season which activate chemicals and give the

crop a head start in covering row middles. When foliage is

insufficient to intercept most of the light, germination and

growth of weed seedlings is promoted.

Peanut yields

In most cases, 1984 treatment yields were lower than

1985. This is to be expected upon examining weed

control data from both years. In 1984, peanuts receiving

some weed control input out-yielded the weedy check (Table

3.4), while at least five systems (6,7,10,11,12) yielded

statistically equivalent to the hand weeded check. Among









Table 3.4. Peanut yield as affected by herbicide systems.

Peanut yield


Treatment No.


1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

LSD


1984 1985

-------- kg/ha ---------


(weedy)

(weed free)

(P=0.05)


2716

2725

2462

2325

1631

2979

2940

2501

2598

2794

3458

3136

2462

2383

478

3439

983


2570

3741

2764

2940

2598

3312

2208

2637

2315

2794

3165

3485

2120

1895

1035

3312

771


aMeans within a column can be statistically
compared using LSD (P=0.05) value located in bottom row
adjacent to each column.
bFor weed control treatments refer to Table 3.1.









these five systems it is important to point out that three

(10,11,12) employed the in-row incorporation technique of

herbicide placement. Similar results occurred in 1985 with

all systems receiving weed control input yielding

significantly higher than the weedy check (Table 3.4). In

addition, 1985 yields show that at least five systems

(2,4,6,11,12) were statistically equivalent in yield to the

hand weeded check. Although the list of systems providing

the highest yields was not identical, systems 6, 11, and 12

were in the high yielding bracket both years of the study.

System 6 (probably the most economical system) included

metolacholor + prometryn preemergence and a paraquat

application mid-postemergence. It is somewhat surprising

that such minimal weed control input allowed such high

yields both years of the study. Systems 11 and 12 were both

in row incorporated treatments. System 11 received benefit

+ vernolate (PPIR), dinoseb (AC), and a post directed

treatment of cyanazine. System 12 consisted of ethafluralin

(PPIR), dinoseb + ethafluralin (AC), and paraquat as a post

directed treatment. Implications of this are that if a

(PPIR) treatment were to be utilized, it must be followed by

an effective cracking spray and even more importantly, a

timely efficacious post directed treatment to address weed

problems within the row middle.

Conclusions.

While many of the systems evaluated were quite

successful, others were not. This study indicates that the









final outcome from weed control treatments is still very

dependent upon prevailing weather conditions as is evidenced

in 1984 and 1985 weed control data differences. This study

does indicate, however, that new methods of incorporation of

chemicals in minimum tillage systems can be quite effective

and could somewhat lessen the weather dependence factor

existent now with many minimum tillage herbicide systems.

Other studies have shown that minimum tillage crops can be

grown successfully under the proper weed management systems.

As a result of these investigations, several probable

herbicide systems have been identified for minimum tillage

peanuts produced under Florida conditions. Presently, the

herbicides prometryne, oryzalin, paraquat and cyanazine are

not registered for use in peanuts.















CHAPTER 4
WEED CONTROL, YIELD AND ECONOMIC ANALYSIS OF
FULL-SEASON AND DOUBLE-CROP PEANUTS GROWN CONVENTIONALLY
AND WITH MINIMUM-TILLAGE





Introduction



In most instances, Southeastern U.S. crop production

schemes have rotated around the production of a particular

crop on a certain piece of land in an annual sequence.

Tradition more than any other factor has contributed to

one crop grown per land area per year. This phenomenon

probably first developed due to man's utilization of

existing wild plants with seasonal or annual production

cycles for food sources. Man slowly began to move these

'wild' plants into areas of his own choosing and cultivated

them for food thereby developing what we have known as

primitive agriculture. The elimination of competing

vegetation around the naturally occurring food plants

probably gave rise to tillage. Since that time, tillage has

come to be an accepted practice and is often considered to

be a necessary requirement for the production of most food

crops.

Developments in recent years have brought about a

reevaluation of tillage requirements. With the advent of









herbicides, tillage is no longer the only method available

to control weeds. In addition, economic pressures to reduce

production costs have brought about a critical examination

of the need for various tillage practices. Interest in

minimum or conservation tillage has continued to expand

since the initiation of studies in Virginia in 1960 by Moody

et al. (42).

Minimum-tillage systems have been shown to reduce

erosion (26,37,60,67), allow acreage expansion into areas

not suited for conventional tillage (5,30,52), reduce energy

requirements needed for crop production (1,16,52,64), and

positively enhance soil moisture conditions and soil water

conservation. Despite these potential advantages, however,

conventional tillage systems were still used on 68% of U.S.

cropland in 1981 (12). The high percentage of cropland

still under conventional production is more than likely due

to the fact that farm-level comparisons of these systems

typically involve trade-offs between lower machinery-related

costs and higher chemical and/or fertilizer costs. Most

studies conclude that farm-level economic feasibility of

reduced tillage systems depends to a great extent upon

managerial skills necessary to obtain yield levels equal to

those from established conventional tillage systems (29,33).

Another advantage associated with minimum tillage is

the ability to plant a crop quickly. The elimination of

costly as well as time-consuming land preparation techniques

allows the grower to plant crops in a "once over the field









manner". The "once over the field" procedure not only

allows the primary crop to be planted in less time, but also

allows the timely planting of a second or double crop

immediately following harvest of the proceeding crop.

Therefore, the potential exists for farming more total crop

acres with little increase in labor, machinery, or land

costs using a minimum-tillage double cropping system.

Loope (35) showed that annual land costs (interest and

taxes), and most machinery and labor costs are usually fixed

and do not increase when land is double cropped. Any return

over variable costs increases profits. The variable or

added costs of producing double-crop soybeans, for example,

represent less than 50 percent of the total production costs

(35). Meanwhile Jeffery et al. (29) point out that while

drastic yield differences may occur from one double-crop

location to another, generally double-cropped soybeans yield

less when planted conventionally than when planted under

minimum-tillage conditions. This gives further credence to

the marriage of minimum-tillage with double crop production

of small grains and agronomic row crops. Jeffery et al.

further point out that successful double cropping requires

skilled management and careful planning. Timing appears to

be of the utmost importance and planting of the second

crop is the most critical operation, both from the

standpoint of time and actual mechanics.

Many small grain, soybean, and corn double-cropping

studies have been done with variable results. Economic









analyses performed on several of these studies identifies

minimum-tillage double cropping as a profitable crop

production alternative (29,33). Few studies (14,15) can be

found which deal with the minimum-tillage production of

peanuts and none that address the questions of double crop

profitability, weed control and eventual peanut yield

obtained in conventional or minimum-tillage culture. These

appear to be crucial questions to address should the

production of minimum-tillage peanuts become accepted by

producers.

This study was designed to compare full-season with

double-crop peanuts planted either conventionally or minimum

tillage and to determine weed control intensity required for

these different cropping systems. In addition, an economic

analysis of these factors was employed in hopes of

identifying the most profitable cropping system.



Materials and Methods



Field experiments were conducted during 1984 in

Williston and Marianna, Florida and during 1985 in Jay,

Florida. The soil type in Williston was a Zuber loamy sand

(Ultic Hapudalf), a Chipola loamy sand (Arenic Hapludult) in

Marianna, and a Red Bay sandy loam (Rhodic Paleudult) in

Jay. The experimental design was a split-plot with four

replications. Whole plots consisted of all combinations of

season and tillage. The 'Sunrunner' peanut cultivar was









planted in all plots using a modified twin 23 cm row spacing

and seeded at a rate of 140 kg/ha. Early season peanuts

were planted approximately May 1 during both years of the

study and late season (double-crop) peanuts were planted

approximately June 10. Tillage treatments were either

conventional or minimum-tillage. The experimental areas at

all three locations had most recently been in peanut

(Arachis hypogaea L.) and soybean [Glycine max (L.) Merr.]

production and were seeded with wheat (Triticum aestivum L.)

in the fall prior to the initiation of the experiments.

Full-season plots were sprayed with 1.12 kg/ai/ha of

glyphosate two weeks prior to peanut planting to kill the

wheat cover and existing weeds. In double-crop treatments,

wheat was allowed to mature normally and then harvested for

economic grain yield.

Three herbicide systems varying in weed control

intensity were assigned to split plots. These systems were

largely based upon established weed control methods utilized

in conventional practices. The major modification was the

elimination of highly volatile dinitroaniline and thio-

carbamate herbicides [e.g. benefin and vernolate], which

require soil incorporation. The herbicide systems investi-

gated are listed in Table 4.1.

Experimental areas contained heavy to mild infestations

of goosegrass [Eleusine indica (L.) Gaertn.], crowfootgrass

[Dactyloctenium aegyptium (L.) Richter], Florida pusley

(Richardia scabra L.), Florida beggarweed [Desmodium






















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tortuosum (SW.) DC.], smallflower morningglory [Jacquemontia

tamnifolia (L.) Griseb.], and sicklepod (Cassia obtusifolia

L.). Soil fertilization and liming practices were in

accordance with soil test recommendations of the University

of Florida Soil Testing Laboratory.

In order to simulate wheat harvest and reduce stubble

height, full-season treatments were mowed before planting

allowing the straw to scatter randomly over the plots.

Double-crop plots were harvested conventionally upon

maturity with straw dispersed uniformly over the plots.

Minimum-tillage treatments were prepared using a modified

Brown-Harden Ro-Till planter with the actual planter units

removed. The modified Ro-Till had a short subsoiler shank

with an attachable slitter bar that penetrated the soil to a

depth of approximately 40 cm. Fluted coulters were mounted

on either side of the shank. The short subsoiler shank and

slitter blade combination opened the soil and destroyed plow

pans beneath the row while fluted coulters smooth the ripped

soil and dissipated large clods. 'Rolling crumblers'

(barrel shaped devices that resemble a stalk cutter) were

mounted immediately behind the fluted coulters. The rolling

crumblers serve to further smooth and shape the seed bed.

Conventionally prepared treatments were implemented with a

moldboard plow set to run approximately 20 cm deep with

repeated diskings thereafter to further smooth the seed bed.

Planting was done in a separate operation due to

equipment limitations. The twin-row pattern was achieved by









using a tool-bar mounted twin-row planter with the planter

units situated 76 cm apart center-to-center on the tool bar.

Herbicides were applied with a tractor mounted, compressed

air sprayer set to deliver 187 L/ha. Fungicide and

insecticide applications were made on an as-needed basis

throughout the season in accordance with accepted

recommendations.

Peanuts were dug in mid to late September of both years

of the study. A conventional digger-shaker-inverter was

used to remove peanuts from the soil. Plots (1.5x7.7M) were

harvested with conventional equipment after three days of

field drying. Data collected included early, mid, and late

season weed control ratings. Weed control ratings were

based upon percent control compared to the check; e.g. 100

to 90%--excellent, 90 to 80%--good control, 80 to 70%--fair

control, and below 70%--unacceptable control. Yield data

from all plots were adjusted to 7% moisture.

Weed control ratings and yield data were subjected to

analysis of variance and means were tested for differences

using Duncan's multiple range test within columns. Yield

means within rows were tested with a Least Significance

Difference Test. Both mean separation techniques were used

at the 5% level of probability. In addition, net returns

for individual treatment yield means were calculated and

converted to $/ha.









Results and Discussion



Weed Control Systems

Three weed control systems were designed to evaluate

three levels of herbicide intensity. System 1 was designed

to be the most intense (both herbicidally and economically).

System 2 was designed to be of medium intensity while System

3 was the least intense system. Analysis of the data

indicated no interactions between level of weed control

intensity and cropping system. Apparently the intensity of

weed control required did not vary with a change in tillage

or time of planting. Because there were no differences

noted, weed control data was averaged over tillage and time

of planting. Differences in weed control between herbicide

systems did occur as will be pointed out in the discussion

of data in tables 4.2 through 4.6.

Peanut injury. At the Jay location, Systems 1 and 3

(Table 4.1) caused only slight early-season crop injury

(Table 4.2). Some injury persisted in these treatments even

up to the late rating period. None of the treatments,

however, received higher than a 10% injury rating. Peanut

injury at the Marianna location followed the same general

trend except that the early season injury was much more

severe (Table 4.2). The increased injury was due primarily

to extremely dry weather conditions which inhibited the

peanuts ability to recover from the early-season herbicide

injury. Systems 1 and 3 (Table 4.1) utilized applications









Table 4.2. Peanut foliar injury as affected by herbicide
system (averaged across season and tillage).

Peanut injury


Jay Marianna Williston
b
-------------------Time of Rating ------------------

TRT #c Early Mid Late Early Mid Late Early Mid Late
----------------------------- ------------------

1 10a 5a 5b 14b 10b 7a 28a la Oa

2 Ob 4a 2bc 5c 5c 3b 2c Oa Oa

3 8a 5a 8a 18a 21a 10a 8b Oa Oa

4 Ob Ob Oc Od Od Ob Oc Oa Oa

aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).

bEarly--30 days after planting, Mid--70 days after
planting, Late--120 days after planting.
CFor weed control treatments refer to Table 4.1.









of paraquat which caused severe peanut damage. Due to the

drought conditions present, peanuts in these treatments did

not overcome this injury season long. Mid-season injury

ratings taken shortly after early postemergence herbicide

applica-

tions actually show an increase in crop injury in System 3

(Table 4.2). System 2 exhibited the least crop injury at

Marianna (Table 4.2). At the Williston location, all three

herbicide systems exhibited injury at the early rating

period. With the help of good growing conditions and ample

rainfall, however, all injury had dissipated by the mid and

late season ratings (Table 4.2). System 1 at Williston

exhibited unusually high injury symptoms at the early rating

but appeared to recover completely.

Annual grass control. Annual grass in all three

locations consisted of uniform infestations of goosegrass

and crowfootgrass. A review of annual grass control data

(Table 4.3) reveals that with the exception of Jay in 1985,

all three systems performed quite well and generally

provided better than 90% season long grass control (Table

4.3). This anomaly of the Jay data can be explained by the

prevailing weather conditions. Within 24 hours of herbicide

application, rainfall began and continued intermittently for

the next 36 hours depositing over 23 cm of precipitation on

the experimental site. This intense rainfall probably

leached the herbicide deep in the soil profile below the

germinating grass seeds. Mid-season ratings show that grass

control was aided somewhat by ground cracking and early









Table 4.3. Annual grass control as affected by herbicide
system (averaged across season and tillage).

Annual grass ratingab


Jay Marianna Williston
-------------------Time of Ratingc-----------------

TRT #c Early Mid Late Early Mid Late Early Mid Late

---- -------------- % -------9a-------

1 87a 94a 85a 97a 96a 92a 99a 99a 99a

2 87a 95a 88a 97a 96a 96a 99a 99a 98a

3 78a 96a 79b 98a 95a 92a 99a 99a 98a

4 Oc Oc Oc Ob Ob Ob Ob Ob Ob


aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).
Annual grass at all locations consisted of
approximately 60% goosegrass and 40% crowfootgrass.

CEarly--30 days after planting, Mid--70 days after
planting, Late--120 days after planting.
For weed control treatments refer to Table 4.1.









postemergence herbicide sprays. Residual control, however,

was clearly lower late season in Jay than in other locations

(Table 4.3). As explained earlier, it appears under normal

conditions all systems may have been too intense to

establish herbicide system intensity most appropriate for

various seasons of production or tillages employed.

Smallflower morningglory control. This weed species

occurred only at the Jay and Marianna locations; therefore,

no ratings are shown for the Williston site (Table 4.4).

Herbicide Systems 1 and 2 (Table 4.1) gave good season long

control of smallflower morningglory while System 3 was not

adequate at either location. Both System 1 and 2 employed a

preemergence herbicide application while system 3 did not

receive a herbicide application until the ground cracking

stage. In most cases, smallflower morningglory was already

present in herbicide system 3 plots. The treatment of

alachlor plus paraquat did not completely kill all plants

present. Alachlor alone as a preemergence herbicide has

been identified as somewhat weak on smallflower morning-

glory. It appears that the lack of a preemergence herbicide

spray and a somewhat weak herbicide on smallflower

morningglory were responsible for unacceptable control in

herbicide System 3 (Table 4.4). Both Systems 1 and 2 (Table

4.1) appear to be adequate for control of this species in

that late season control at both locations was still in

excess of 90%.









Table 4.4. Smallflower morningglory control as affected by
herbicide system (average across season and tillage).

Smallflower morningglory ratinga


Jay Marianna Williston
----------------- Time of Rating --- -----------

TRT #c Early Mid Late Early Mid Late Early Mid Late

------------------------- % ------------------------

1 99a 98a 97a 99a 96a 96a -- --

2 97a 99a 98a 98a 94a 95a -- -- --

3 87b 80b 75b 70b 68b 60b -- --

4 Oc Oc Oc Oc Oc Oc -- -- --

aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).

bEarly--30 days after planting, Mid--70 days after
planting, Late--120 days after planting.
cFor weed control treatments refer to Table 4.1.








Sicklepod control. All systems performed unusually

well with respect to sicklepod control (Table 4.5). Ratings

in excess of 95% were common in the early season at both

Marianna and Williston. Ratings in excess of 90% persisted

throughout the growing season. None of the systems selected

commonly provide for control to this superior degree.

Excellent control was probably due to good activating

rainfall after each preemergence herbicide application both

years. In addition, sicklepod populations were very low at

both Marianna and Williston with no sicklepod occurring at

the Jay site. Under heavier sicklepod pressure, control

from these systems would more than likely have been much

lower than observed in these studies.

Florida beggarweed control. Florida beggarweed

occurred in significant amounts at both Jay and Marianna.

Insufficient and erratic populations occurred in Williston

making it difficult to obtain accurate control results. As

with sicklepod, Florida beggarweed was adequately controlled

with all three systems (Table 4.6). All systems, with the

exception of System 2 at Jay, allowed 90% control even as

late as 120 days after planting. Florida beggarweed is not

generally an early season weed control problem as the

majority of its seeds do not germinate until soil tempera-

tures increase later in the spring. Early and late

postemergence treatments employed in all three systems

(Table 4.1) appear to have offered adequate mid to late

season control. When examining the weedy checks, higher









Table 4.5. Sicklepod control as affected by herbicide
system (averaged across season and tillage).

Sicklepod ratinga


Jay Marianna Williston

------------------Time of Rating -----------------

TRT #c Early Mid Late Early Mid Late Early Mid Late

------------------------- % -----------------------

1 --- --- --- 99a 96a 97a 99a 95a 93a

2 --- --- --- 99a 98a 96a 99a 96a 94a

3 --- -- --- 99a 94ab 95a 99a 97a 97a

4 -- --- --- Ob Oc Ob Ob Ob Ob


aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).

Early--30 days after planting, Mid--70 days after
planting, Late--120 days after planting.

cFor weed control treatments refer to Table 4.1.









Table 4.6. Florida beggarweed control as affected by
herbicide system (averaged across season and tillage).

Florida beggarweed ratinga


Jay Marianna Williston
------------------Time of Rating ----------------

TRT #c Early Mid Late Early Mid Late Early Mid Late

------------------------- % ----------------------

1 99a 99a 99a 99a 96a 97a -- -- --

2 99a 94b 86b 98a 98a 94a -- --

3 99a 99a 96a 94b 95a 94a -- --

4 Ob Oc Oc Oc Ob Ob -- -- --

aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).
bEarly--30 days after planting, Mid--70 days after
planting, Late--120 days after planting.
cFor weed control treatments refer to Table 4.1.









populations of Florida beggarweed were observed to occur in

conventional tillage plots than in minimum-tillage plots.

This may be because of uniform soil mixing and stirring in

these treatments.

Overall, weed control ratings from all species with the

exception of smallflower morningglory were very good with

all three systems chosen. This shows that there presently

exist treatment combinations which can handle weed control

problems in southeastern conventional as well as minimum-

tillage peanuts regardless if produced full season or double

crop.

Peanut Yield and Net Returns Marianna

Yields from all systems were universally depressed

(Table 4.7) at the Marianna location due to prolonged and

intense drought at this location during the 1984 season.

Although weed control differences among herbicide systems

have been difficult to identify, yield differences at

Marianna clearly differentiate System 2 as being superior

(Table 4.7). System 2 gave highest yields whether full-

season or double-crop as compared to other herbicide

systems. Within herbicide System 2, the LSD comparison

statistic shows full-season conventional production to be

superior to all other season by tillage combinations. At

Marianna, double-cropped peanuts were planted in a drought

stressed environment and were never under adequate growth

conditions until very late in the season. These adverse

weather conditions are reflected directly in low peanut









Table 4.7. Effect of season, tillage, and herbicide system on
peanut yield and net return at Mariannna, Florida 1984.

Peanut yield and net returnab,


Full-Seasond

Minimum-Till Conventional

TRT#9 Yield Return Yield Return

kg/ha $/ha kg/ha $/ha

1 1817a -121 2570bc 250

2 2462a 284 3830a 1020

3 2237a 168 2833b 448

4 2140a 229 2120c 97


Double-Cropef

Minimum-Till Conventional

Yield Return Yield Return

kg/ha $/ha kg/ha $/ha

1602a -186 1983a 37

1944a 38 1944a 38

742b -658 762b -720

1378a -162 1208b -340


aMeans followed by different letters within a column are
significantly different according to Duncan's multiple range test
(P=0.05).
byield means within rows can be compared with an LSD (0.05)
value = 624.
cNet returns are calculated using 1985 2:1 contract quota
peanut prices using modified University of Florida peanut cost of
production budgets and 1985 herbicide prices.
dpeanuts planted approximately May 1.

peanuts planted approximately June 10.

fDouble-crop net return calculations take into account
economic benefit received from the sale of an avg. 2345 kg/ha
wheat grain crop.

gFor weed control treatments refer to Table 4.1.









yields from all double cropped systems (Table 4.7).

Although visual weed control was nearly equal for all

species, with the exception of smallflower morningglory,

large yield differences occurred between herbicide systems.

Much of this was due to peanut injury which was never

completely overcome by the plants, as well as the fact that

System 3 had very high smallflower morningglory populations.

Net return for double-crop production in the Marianna

test would be virtually profitless with most systems

actually exhibiting a net loss (Table 4.7). Among

double-crop treatments, System 2 minimized losses better

than the other systems. Peanuts produced full-season were

profitable in most cases (Table 4.7). Net returns are tied

directly to peanut yield and intensity of herbicide system.

Systems which gave the best yields also had the highest net

returns. Among full-season treatments, conventional tillage

treatments were generally more profitable. Conventional

production under System 2 (Table 4.1) would have returned

$1020 per hectare to the grower. This particular system was

twice as profitable as any other system at the Marianna

location in 1984 (Table 4.7).

Peanut Yield and Net Returns Jay

Weather conditions at Jay during 1985 were much better

than Marianna as is reflected in overall yields (Table 4.8).

Again, full-season production yields were much better than

than those of double-cropped peanuts. Few significant yield

differences occurred with respect to herbicide system









Table 4.8. Effect of season, tillage, and herbicide system on
peanut yield and net return at Jay, Florida 1985.

Peanut yield and net returnabc


Full-Seasond

Minimum-Till Conventional

TRT#g Yield Return Yield Return

kg/ha $/ha kg/ha $/ha

1 3888a 1109 4103b 1161

2 4641a 1578 5344a 1919

3 3879a 1143 4465ab 1418

4 2482b 432 2101c 86


Double-Cropef

Minimum-Till Conventional

Yield Return Yield Return

kg/ha $/ha kg/ha $/ha

2745a 492 3888a 1095

3370a 885 3741a 1029

2433a 356 2990ab 603

2667a 604 2140b 171


aMeans followed by different letters within a column are
significantly different according to Duncan's multiple range test
(P=0.05).
Yield means within rows can be compared with an LSD
(0.05) value = 833.
CNet returns are calculated using 1985 2:1 contract quota
peanut prices using modified University of Florida peanut cost of
production budgets and 1985 herbicide prices.
dpeanuts planted approximately May 1.

Peanuts planted approximately June 10.

fDouble-crop net return calculations take into account
economic benefit received from the sale of an avg. 2345 kg/ha
wheat grain crop.

gFor weed control treatments refer to Table 4.1.









regardless of tillage or season of growth. The lack of

yield differences in Jay follows the previously identified

weed control trends. In most cases, full-season peanuts

out-yielded double-cropped counterparts by as much as 1000

kg/ha (Table 4.8). Double-cropped peanuts were planted

under adequate soil moisture and growing conditions were

good throughout the season. Yield differences were probably

due to the reduction in photosynthetically active radiation

and cooler temperatures during the pod fill period.

Regardless of the season or tillage examined, herbicide

System 2 (Table 4.1) allowed superior yields in the test at

Jay as it did at the Marianna location. (Table 4.8).

Net returns per hectare again identify full season

production as the most profitable with herbicide System 2

treatments showing the highest net return within full-season

production. Double-cropped peanuts were not as profitable

as full season. At Jay, significant dollars were returned

compared to very poor returns from double-cropped peanuts in

Marianna (Table 4.7). Here, every double-crop system

provided a profit but not as much as the full-season

treatment counterparts. Among full-season treatments,

conventional plots generally yielded numerically higher.

The LSD value (833), however, shows few significant

differences with respect to yield within a herbicide system

whether produced with minimum or conventional tillage (Table

4.8). Net returns for the highest yielding system clearly










show a larger profit margin under conventional peanut

production using herbicide System 2.



Peanut Yield and Net Returns Williston

Peanuts planted in Williston performed differently than

in the other locations with respect to yield and net return.

Here, full-season peanuts were planted under poor moisture

conditions which persisted for up to 25 days after the

peanuts emerged. Conversely, double-cropped peanuts were

planted into good soil moisture, sufficient rainfall

occurred throughout the season and these peanuts never

underwent a stress period. Williston, the southern most

experimental location, enjoys warmer temperatures later in

the season than either of the other two locations.

Therefore, peanuts in the Williston test had equivalent

yields whether produced full-season or double-cropped (Table

4.9, LSD=694). Rainfall patterns occurring at this site are

very typical for this area during the time of year peanuts

were planted. Under these conditions it may be as

profitable or more profitable to double-crop peanuts after

the harvest of a wheat crop. Williston yields also

correlate quite well with weed control trends in that few

significant differences occurred with respect to herbicide

systems (Table 4.9). Whether full-season or double-cropped,

peanut yields, although not statistically significant, are

generally numerically higher for the herbicide System 2

treatments. Another factor apparent is that minimum-tillage









Table 4.9. Effect of season, tillage, and herbicide system on
peanut yield and net return at Williston, Florida 1985.

Peanut yield and net returnabc


Full-Seasond

Minimum-Till Conventional

TRT#g Yield Return Yield Return

kg/ha $/ha kg/ha $/ha

1 3654ab 970 3557ab 836

2 4729a 1630 4191a 1234

3 3429b 876 4055a 1174

4 3781b 1204 2951b 591


Double-Cropef

Minimum-Till Conventional

Yield Return Yield Return

kg/ha $/ha kg/ha $/ha

3840a 1143 4152a 1252

4387a 1489 3722ab 1017

3986a 1269 4210a 1328

1710b 30 2882b 612


aMeans followed by different letters within a column are
significantly different according to Duncan's multiple range test
(P=0.05).
byield means within rows can be compared with an LSD (0.05)
value = 694.

CNet returns are calculated using 1985 2:1 contract quota
peanut prices using modified University of Florida peanut cost of
production budgets and 1985 herbicide prices.
dpeanuts planted approximately May 1.

Peanuts planted approximately June 10.

Double-crop net return calculations take into account
economic benefit received from the sale of an avg. 2345 kg/ha
wheat grain crop.

For weed control treatments refer to Table 4.1.









treatments under System 2 had numerically higher yields than

conventional tillage treatments. This may be due to better

moisture conservation and less combined evapotranspiration

under the minimum-tillage plots where row middles were

covered with wheat straw.

Williston location net returns were also highest under

herbicide System 2 (Table 4.1). This trend is evidenced at

all three locations, though at Williston, highest returns

are seen in minimum-tillage plots (Table 4.9). The most

profitable system was minimum-tillage peanuts grown

full-season under herbicide System 2 (Table 4.9). With the

exception of weedy checks, all other treatments showed very

good net return to the grower.

Overall Net Return Analysis

Combined net returns from all locations are presented

in Table 4.10. These results indicate that full-season

production of peanuts will be the most profitable.

Full-season production plus conventional land preparation

techniques had greater profit returns than minimum-tillage

techniques, with the exception of completely weedy treat-

ments (Table 4.10). Apparently some degree of weed control

was obtained in minimum-tillage plots due to less soil

disturbance and weed seed exposure to the surface and the

mulch effect of the wheat residue. However, when herbicide

weed control input is added this trend is over shadowed.

Among the systems tested, net returns indicate that

herbicide System 2 (Table 4.1) was the most profitable at

all locations.









Table 4.10. Herbicide system net returns as affected by
season and tillage (averaged across all locations).

Production system returns $/haa


Full-Seasonb

TRT#d Minimum-Till Conventional

1 $ 653 $ 749

2 $1164 $1391

3 $ 729 $1013

4 $ 622 $ 258


Double-Crop-

Minimum-Till Conventional

$ 483 $ 770

$ 804 $ 669

$ 322 $ 404

$ 158 $ 148


production system returns are calculated using average
yields from all three experimental locations using 1985 2:1
contract quota peanut prices using modified University of
Florida peanut cost of production budgets and 1985 herbicide
prices.
peanuts planted approximately May 1.

cPeanuts planted approximately June 10.

dFor weed control treatments refer to Table 4.1.









Overall Season of Production Effects

Data from Jay and Marianna indicate full-season

production to be superior to double crop production (Table

4.11). Data from Williston indicate season of production

had little effect on peanut yield. Peanuts produced under

more northern conditions may be adversely affected by later

planting dates, while peanuts grown further south may be

able to tolerate later planting dates and yield equally as

well as earlier planted peanuts.

Overall Tillage Effects on Peanut Yield

Although numerically higher, yields of conventional

tillage were statistically equivalent in peanut yield to

minimum tillage at Jay and Williston (Table 4.12). This is

encouraging especially for areas of the state where peanuts

are presently being produced on marginal lands with high

erodability. Results from these two locations indicate that

production would be equal whether minimum-tillage or conven-

tional. With these data taken into account, it may be

desirable for a grower to employ minimum-tillage techniques

on highly erodable lands. However, peanut yields in

Marianna indicate that conventional tillage practices were

superior to minimum-tillage techniques (Table 4.12). While

this factor may be true, it is important to reiterate that

extremely dry conditions existed at planting time and, as a

result, the minimum-tillage planter could not be operated at

a depth equal to that used at other locations. Further work

may reveal that this yield difference was primarily due to

lack of root penetration through the soil hard pan.






69


Table 4.11. Effects of season of production on peanut yield
(averaged across tillage, herbicide systems and locations).

Peanut yield



Season Jay Marianna Williston
----------------kg/ha------------------

Full-season 3863a 2501a 3793a

Double-crop 2997b 1455b 3610a

aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).
bFull-season--peanuts planted approximately May 1,
Double-crop--peanuts planted approximately June 10.










Table 4.12. Effects of tillage on peanut yield (averaged
across seasons, herbicide systems and locations).
Peanut yield


Tillage Jay Marianna Williston
------------- kg/ha---------------

Minimum-till 3263a 1790b 3668a

Conventional 3596a 2165a 3715a

aMeans followed by different letters within a column are
significantly different according to Duncan's multiple range
test (P=0.05).












CHAPTER 5
EFFECTS OF TILLAGE AND WHEAT STRAW LEACHATES ON THE
GERMINATION AND INCIDENCE OF SCLEROTIUM ROLFSII IN PEANUTS





Introduction



Stem rot in peanuts, also known as white mold, southern

stem rot, southern blight, and Sclerotium rot is caused by

the fungus (Sclerotium rolfsii Sacc). The disease is found

in virtually all major peanut producing areas of the world.

This fungus, isolated from the branches of diseased peanuts

in 1911 by Saccardo (58), is one of the most important

soilborne pathogens of peanuts. Yield losses typically do

not exceed 25% but at times may be as great as 80%. Stem

rot is generally characterized as erratic in occurrence

(50). In one season, the disease may considerably damage

the crop while the next year in the same location, damage

may be only slight.

Early workers emphasized the importance of sanitary

measures in reducing losses. Rolfs (56,57) cautioned that

plants infected early in the season furthered the spread of

the organism and recommended burning "on the spot".

Starving the fungus by elimination of weed hosts (39,53) and

providing for rapid decomposition of organic matter were

also recommended (20,47,61,65). Perry et al. (48) pointed









out that in the case of peanuts, the control of leaf

diseases is of considerable importance in combatting S.

rolfsii. Early harvesting has been suggested in some areas

for several crops (3,23,24,36) which begin to mature before

soil temperatures become highly favorable for S. rolfsii

development. This practice, however, may result in reduced

quality and yield.

Few data exist from controlled experiments on the

effects of seed bed preparation on S. rolfsii. However,

both research and extension agronomist presently recommend

that soil be thoroughly and completely prepared before

planting peanuts (63). Boyle (6,7) popularized a so called

"deep turning; non-dirting" method of peanut culture so as

to reduce losses because of stem rot and root rot

(Rhizoctonia spp.) in peanuts. The objective was to plow in

such a way that all infected organic litter was buried to a

depth of at least 10 cm prior to planting and cultivate the

crop so as to achieve minimal crop-soil contact. Boyle and

Hammons (8) reported that turning with a mold boardplow

produced higher yield and less disease occurrence compared

to tillage with a disk harrow. Garren (21) and Garren and

Duke (22) reported a marked increase in yield and reduction

of diseased plants as a result of deep turning of plant

residues and preventing the movement of soil or plant

residues toward peanut plants during cultivation. While

both practices were important, a larger increase in yield

was attributed to non-dirting cultivation. This suggests









that preventing soil from contacting the peanut branches may

play a larger role in stem rot control than the actual

burial of plant residue through deep mold board plowing.

Therefore, minimum tillage production of peanuts without

moldboard plowing or cultivation of any sort may possibly

further decrease the incidence of stem rot.

Mixon (41), in a four year experiment at Headland,

Alabama (1957 to 1960), found no increase in yield from

different tillage methods in the first three years. In 1960,

however, an increase in yield was detected from deep turning

and non-dirting cultivation, partially due to disease

reduction. In contrast, Harrison (25) states that complete

burial of surface organic matter in Texas is not practical

because such treatments expose the land to severe wind

erosion and does not consistently increase yield.

Most growers in the Southeast utilize "deep-turning;

non-dirting cultivation" techniques in production schemes

coupled with prophylactic chemical treatments of PCNB or

carboxin to control stem rot in peanuts. Chemical treatment

will commonly be applied if peanuts are grown in an area

known to have been infested by S. rolfsii in previous years.

Chemical treatments may cost as much as $150/ha and if no

disease develops in the area, the grower feels he has wasted

money. On the other hand, if disease does occur within an

area, only those growers who have previously treated may

harvest a profitable yield. The erratic pattern of

occurrence of this disease may cause growers to chance not










applying expensive chemical control. Some years this gamble

may pay off but in other years, this may prove to be a

disastrous decision.

Recent research work has shown that the treatment of

peanuts with benomyl may lead to greater stem rot problems

than peanuts treated with other fungicides, primarily

because benomyl reduces soil populations of antagonistic

Trichoderma spp. (51). In addition, Beute and Rodriguez-

Kabana (4) have shown that volatiles of remoistened peanut

hay increase germination of sclerotia five-fold over

sclerotia wetted with deionized water. They further

interject that volatiles, especially methanol from senescent

or dead peanut leaves at the base of the plant, may enhance

sclerotial germination in the soil to a depth of more than 2

cm possibly causing an increase in the incidence of the

disease. These recent discoveries made the investigation of

the occurrence of stem rot in minimum-tillage (MT) peanuts

very interesting. Several researchers (13,40, Personal

communication, Dr. B. J. Brecke, AREC Jay, FL. 32565;

Personal communication, Dr. D. L. Wright, NFREC, Quincy, FL.

32351) have reported that S. rolfsii occurs no worse and at

times to a lesser extent in MT treatments as compared to

conventionally produced peanuts. Possible reasons for this

could be that minimum-tillage plots may offer a more

favorable environment for proliferation and growth of

antagonistic Trichoderma spp. which have been shown to slow

or inhibit the growth of S. rolfsii, and volatile leachates








that have been reported (34) to exist in wheat and rye straw

may be triggering the destructive germination of sclerotia

at or soon after the planting of the peanut crop. In most

areas of the southeastern peanut belt, the spring planting

season is often characterized by extremely dry periods. The

occurrence of these unpredictable extended droughts

following short afternoon showers could cause artificially

stimulated sclerotia to germinate prematurely. The onset of

dry weather might stop their growth before new regenerative

structures can be produced.

With recent research findings and these basic

hypotheses in mind, it was the objective of this experiment

to determine under field conditions if variations in surface

tillage have an effect on the incidence of stem rot; and to

determine in the laboratory, if wheat straw leachates

significantly affect the germination of the sclerotia of S.

rolfsii.



Materials and Methods



Field Studies

Field experiments were conducted during 1984 at Quincy,

Florida and during 1985 at Branford, Florida. The soil type

in Quincy was a Norfolk sandy loam (Ultic Hapludult) and in

Branford, was a Blanton fine sand (Grossarenic Paleudult).

At the Branford location, identical studies were conducted

under both dryland and irrigated conditions. The









experimental design was a randomized complete block with

four replications. The 'Florunner' peanut cultivar was

planted in all plots using a 76 cm row spacing during

mid-May at a seeding rate of 140 kg/ha. Peanuts were

planted using a conventional, minimum-tillage, or no-tillage

system. The experimental area in Quincy had most recently

been in corn (Zea Mays L.) production while the Branford

irrigated location had been in peanuts (Arachis hypogaea L.)

for the past three years. The Quincy and Branford irrigated

locations were seeded with wheat (Triticum aestivum L.) in

the fall prior to initiation of the experiments while the

Branford dryland location was planted directly into a

desiccated bahiagrass sod. All plots were sprayed with 1.12

kg/ai/ha of glyphosate two weeks prior to planting to kill

the cover crop and existing weeds.

The entire test area was treated with pendimethalin

1.12 kg/ha (preemergence), alachlor + dinoseb + naptalam

3.36 + 1.68 + 3.36 kg/ha (ground cracking), dinoseb 0.84

(early post emergence) and 2,4-DB 0.28 (late post emergence)

both years of the study. Any escaped weeds were pulled by

hand. Soil fertilization and liming practices were in

accordance with soil test recommendations of the University

of Florida Soil Testing Laboratory.

In order to simulate wheat harvest and reduce stubble

height, the experimental area at Quincy was mowed before

planting allowing the straw to settle randomly over the

plots. Wheat cover at the Branford irrigated location was









very sparse as cattle had grazed the stubble to a height of

7 to 10 cm. Conventional tillage treatments were

established using a moldboard plow set to run approximately

20 cm deep with repeated diskings thereafter to further

smooth the seed bed. In addition, conventional plots

received two mechanical cultivations using flat sweeps

during the growing season. Minimum tillage treatments were

prepared using a modified Brown-Harden Ro-Till planter with

the actual planter units removed. The modified Ro-Till

consists of a short subsoiler shank with an attachable

slitter blade combination which opens the soil and destroys

plow pans beneath the row while fluted coulters smooth the

ripped soil and dissipate large clods. 'Rolling crumblers'

(barrel shaped devices that resemble a stalk cutter) were

mounted immediately behind the fluted coulters. The

'rolling crumblers' serve to further smooth and shape the

seed bed. The area tilled surrounding the row was

approximately 30 cm wide. No-tillage treatments were

prepared using a KMC no-tillage planter with actual planter

units removed. The KMC unit employs a single long subsoiler

shank (40 cm) directly beneath the row which performs

similarly to the Ro-Till" system. Small rubber tires are

mounted on each side of the subsoiler shank to press soil

back into the subsoiler channel. This system tills an area

approximately 6 cm wide directly beneath the row with a

minimum area of soil disturbed.









Planting was done in a separate operation due to

equipment limitations. All chemicals were applied using a

tractor-mounted, compressed air sprayer set to deliver 187

L/ha. Fungicide and insecticide applications were made on an

as-needed basis throughout the season in accordance with

accepted recommendations.

Due to the lack of an experimental area in 1984

adequately infested with Sclerotium rolfsii, the fungus was

grown in the laboratory and transferred to field plots in

Quincy during 1984. An initial isolate known to be

virulent, was taken from a five year old soil sample, plated

on PDA (potato dextrose agar), and allowed to form mycelia.

Oat seeds were obtained, allowed to embibe water, and

autoclaved twice to kill any existing bacteria or fungi that

might be present. Individual plugs of mycelium were taken

from the isolate growing on PDA and placed into each flask

of oat seed. Flasks were incubated at room temperature for

approximately three to four weeks until the fungus began to

produce numerous sclerotia. At this time, the flasks were

emptied onto the laboratory bench and allowed to dry. With

the drying process, the sclerotia began to mature first

turning a white color, then brown, and finally turning a

deep brownish-black. After drying, the mixture of oats and

sclerotia were divided into twelve equal portions for

distribution on the field plots. Plots were inoculated when

peanuts were approximately 55 days old. Laboratory-grown

sclerotia were introduced into two rows and a row middle in









each plot. Peanuts were then allowed to grow normally for

the remainder of the growing season. The 1985 experiments

at Branford were placed in area known to have been infested

with S. rolfsii over a previous 25 year history of peanut

production. Therefore, no laboratory grown sclerotia were

introduced.

Peanuts were dug in mid-September of both years of the

study. A conventional digger-shaker-inverter was used to

remove peanuts from the soil. Plots (1.5 x 7.7M) were

harvested with conventional equipment after 3 days of field

drying.

Data collected include stem rot disease loci designated

as 'hits' (one hit is equal to a 30 cm or less continuous

length of row infected) and final peanut yield (adjusted to

7% moisture).

Stem rot hit counts and peanut yields were subjected to

analysis of variance and treatment means were tested for

differences using Duncan's multiple range test (P=0.05).

Laboratory Studies

Laboratory studies were initiated to determine the

effects of wheat straw leachate on the germination of S.

rolfsii sclerotia. Wheat leachates were prepared using

harvested wheat straw that had been chopped in a Wiley mill

into lengths of 0.5-1.0 cm. Fifty grams of wheat straw were

placed in 2000 ml erlenmeyer flasks with a sufficient amount

of distilled water to cover the straw. Flasks were then

placed on an orbital shaker for a 6 hour period. Leachate









was then filtered through cheese cloth once and four times

through Whatman #1 filter paper to remove any particulate

matter. The clear amber leachate was then placed in plastic

bottles and frozen until use. Sclerotia were placed on

field soil arranged over a 1 mm wire mesh screen that had

been fitted over the top of a 250 ml beaker. This system

allowed for the wetting of the sclerotia and soil to field

capacity with excess liquid passing through the 1 mm mesh

screen into the beaker below. Treatments consisted of 18

month old sclerotia and one month old sclerotia exposed to

distilled water, wheat leachate, and a 1:100 methanol water

solution. The methanol/water treatment solution has been

used in past experiments as a stimulatory treatment and

generally will give higher germination rate of sclerotia as

compared to distilled water (Personal communication, Dr. F.

M. Shokes, NFREC, Quincy, FL. 32351). Beakers containing

sclerotia were placed in a lighted incubator set to a 15

hour light period and a 9 hour dark period. Ambient

temperature was maintained at 28 C. Beakers were removed

after 24 hours and 48 hours with germination counts being

made by observing mycelial tufts radiating from actively

growing sclerotia.

Data taken included germination counts which were

subjected to analysis of variance. Treatment means were

tested for differences using Duncan's multiple range test at

the 5% level of probability.









Results and Discussion



Stem Rot Hit Counts

Infection loci were measured in terms of stem rot hits

(one hit is equivalent to a diseased portion of a row 30 cm

or shorter in length). The 1984 data from Quincy show a

significantly higher number of stem rot hits in conventional

plots than in minimum or no-tillage treatments (Table 5.1).

Although growth of S. rolfsii was quite successful in the

laboratory, when the fungus was introduced into the field,

the degree of success in establishment and growth was

somewhat lower as is reflected in the overall low number of

hits in all treatments during 1984 (Table 5.1). The fungi

seemed to do well for approximately one week after

introduction into the field with mycelia present on the soil

surface. Even with repeated irrigation to maintain a

favorable environment for fungal growth, the fungus never

seemed to spread from the initial inoculation points and was

not overtly virulent on the peanut plants. The fungus did

not appear to be attacked in the field by other fungi or

bacteria; rather, it appeared to simply lie dormant in a

state of mycelial rest. It is interesting to note that

conventional tillage in Quincy had the highest hit counts

possibly due to cultivation in these plots which may have

aided in the disease spread.

The Branford irrigated study in 1985 reflects somewhat

different trends in stem rot hit counts. Although numerical










Table 5.1. Stem rot hit counts as influenced by tillage
treatment.

Stem rot hitsab


Tillage 1985 Branford 1985 Branford
Treatment 1984 Quincy irrigated dryland Avg.

-------------# hits/7.7M row----------------

Conventional 1.8a 1.7a 2.0a 1.8

Minimum-till 0.2b 2.8a 3.0a 2.0

No-till 0.2b 1.8a 4.0a 2.0


aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).
bone hit consists of an infected portion of row 30 cm
or less in length.


cHit counts are averages from four replications.










difference did occur, no statistical differences in stem rot

hit numbers were evidenced between tillage treatments (Table

5.1). A trend toward larger numbers of disease loci,

however, was noted in minimum and no-tillage plots. This

trend is opposite that of 1984 data from Quincy.

Highest stem rot hits were noted in the Branford

dryland experiment (Table 5.1). Results from this location

are similar to those from the Branford irrigated area. This

is probably due to the reluctance of the cooperating grower

to utilize the irrigation system at the location where

available. As a result, irrigated and dryland are more

fitting when used to describe the production areas and not

the practices as far as soil moisture maintenance is

concerned. Although the season was extremely dry, the

grower chose to irrigate only twice, both times when the

peanuts were near death. Although actual stem rot hit

counts were higher at the dryland location, there was still

no significant difference in hit counts due to tillage

treatment (Table 5.1). Previous researchers have

hypothesized that the lower appearance of soilborne disease

in minimum-tillage practices may have been due to

allelopathic leachates rinsed from existing straw mulch

(Personal communication, Dr. D. G. Shilling, Agronomy,

Dept., Univerisity of Florida, Gainesville, FL., 32611).

This may well have been the case at the Quincy location

which lead to the poor establishment of the disease. Straw

levels at the Branford irrigated location, however, were










very low. Failure to establish the disease in the Branford

location was clearly due to other factors which seem to have

had little to do with allelopathic leachates or antagonistic

fungi. Poor establishment and erratic hit counts at

Branford could possibly have been due to impending dry

weather and overall harsh growing conditions. Even under

these conditions both reduced tillage treatments contained

numerically higher stem rot hits.

Peanut Yields

Plots at all three locations were eight rows wide by

7.7 M in length with the two center rows harvested at each

location. This coincides with rows that were inoculated

with S. rolfsii at the Quincy location.

Replication within treatment variation at Quincy was

extremely high (C.V.=35); therefore, no significant

differences in yield were noted though lowest to highest

treatment yields differed by over 1000 kg/ha (Table 5.2).

Minimum-tillage plots yielded over 700 kg/ha better than the

no-tillage treatment as well as out yielding conventional

tillage over 1000 kg/ha (Table 5.2). Plots with the lowest

number of stem rot hits yielded the highest at Quincy

(Tables 5.1 and 5.2).

Neither study at the Branford location exhibited

statistical differences in peanut yields with respect to

the tillage system used (Table 5.2). In the Branford

irrigated study, only 60 kg difference in yield occurred

regardless of tillage system. Yields from this location









Table 5.2. Peanut yield as affected by tillage treatment.

Peanut yield


Tillage 1985 Branford 1984 Branford
Treatment 1984 Quincy irrigated dryland Avg.
----------------- kg/hab -------

Conventional 3029a 3361a 3107a 3166

Minimum-till 4143a 3390a 2951a 3495

No-till 3370a 3332a 2794a 3165

aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).
byields are averages from four replications.









correlate nicely with the fact that no differences were seen

with respect to stem rot hit counts at the irrigated

location (Table 5.1). Peanut yields in the Branford dryland

location were similar to the irrigated location although a

wider margin was noted between the high and low yielding

treatments. While no statistical differences were seen with

respect to yield, conventional plots had higher yields than

minimum and no-tillage plots (Table 5.2). No statistical

difference was noted for stem rot counts at this location.

It is interesting to note that treatments with the highest

stem rot hit counts actually yielded the least (Table 5.1

and 5.2).

Overall Conclusions of Field Studies

Data trends conflict from year to year and location

to location in this study. This phenomenon has been

observed by other researchers who have endeavored to work

with S. rolfsii (Personal communication, Dr. F. M. Shokes,

NFREC, Quincy, FL. 32351). The extremely erratic nature of

this fungus makes it very difficult to obtain and interpret

meaningful data over a period of a two year study. Trends

in data conflict most in the area of stem rot counts while

peanut yield data indicates that the tillage system did not

have a drastic effect on yields. Steadfast conclusions

related to the occurrence of S. rolfsii due to tillage type

are very difficult to make from data presented. However,

indications are that significant differences in yield will

not be seen through the use of minimum-tillage peanut

practices.










Overall Conclusions of Laboratory Studies

Laboratory studies were conducted in order to test

whether wheat straw leachates may have a stimulatory effect

on sclerotia germination similar to that reported for a

1% methanol solution. If in fact sclerotia could be caused

to germinate early in the season due to stimulation by straw

leachates when no active source of food was available, the

sclerotia might perish before being able to produce viable

reproductive bodies. This may be one of the reasons

researchers working with minimum-tillage peanuts have noted

less stem rot in their experiments. Studies on sclerotial

germination were conducted under uniform conditions three

times and each treatment was replicated four times. Means

presented in Table 5.3 represent 12 observations each.

Eighteen month old sclerotia responded variably to

wetting solutions at the 24 and 48 hour counting periods.

After 24 hours sclerotia treated with wheat leachate had

germinated at a significantly higher rate than those treated

with distilled water or methanol/water solutions (Table

5.3). Counts made 48 hours after initiation of the

experiments reveal that overall germination had increased

very little in the wheat leachate treatments; however,

germination in the methanol/water treatment had increased to

levels equivalent to wheat leachates. Sclerotia exposed to

distilled water increased slightly in germination over the

24 hour period. This treatment was significantly lower in

sclerotia germinated after 48 hours when compared to the





88


Table 5.3. Stem rot sclerotial germination as affected by
sclerotial age and wetting source.

Sclerotial germinationab


---------Sclerotial age--------

Wetting Source 18 month 1 month

------------% germination--------------

24 hr 48 hr 24 hr 48 hr

Distilled H20 56b 63b 3b 88ab

Wheat leachate 74a 76a 28a 77b

Methanol/water 58b 74a 3b 95a

aMeans followed by different letters within a column
are significantly different according to Duncan's multiple
range test (P=0.05).
Sclerotial germination counts taken from three
identical experiments conducted within a two month time
interval, treatments were replicated 4 times in each
experiment. Each represents 12 observations.









other two wetting sources (Table 5.3). Results indicate a

fairly rapid response in germination by these two treatments

when compared to distilled water treatments of S. rolfsii

reproductive bodies. This evidence may suggest a more

uniform germination of existing sclerotia which could be

detrimental if conditions for infection of peanuts do not

persist at the time of initial germination. Peanuts

produced through minimum-tillage methods where sufficient

straw is present and adequate rainfall occurs to wash

leachates from the straw may experience the same phenomenon

shown in laboratory studies. This uniform germination may

deplete the soil bank of viable sclerotia to infect the

peanut crop at some point later in the growing season when

the peanut plant is more vulnerable. Studies with 18 month

old sclerotia closely mimic the approximate age of the S.

rolfsii reproductive bodies present in an every other year

peanut rotation.

Experiments were also conducted using sclerotia that

were approximately one month old to determine if any

dormancy factor might be involved in the growth and

infection patterns of stem rot of peanuts. Initial

non-replicated observations with 18 month old sclerotia

exposed to the three wetting sources had revealed good

germination regardless of the wetting source used. This

initial observation lead to the belief that if any dormancy

factor was involved in sclerotial germination, it had been

overcome by the age and drying process of the 18 month old









sclerotia. With this in mind and before replicated studies

had been conducted, it was decided to include fairly young

sclerotia to determine if any dormancy mechanisms might be

influenced by the wetting solution on sclerotia that perhaps

were not biologically ready in germinate. As has been

previously discussed, initial non-replicated observations

have been found in error. This is evidenced by the fact

that wetting solutions indeed have an effect on germination

of 18 month old sclerotia (Table 5.3).

Twenty-four hour germination counts on 1 month old

sclerotia reveal some very interesting results. It appears

that these young sclerotia do have some dormancy mechanism

as is indicated by the overall low germination percentages

from all treatments at the 24 hour period (Table 5.3). In

all cases, these counts are as much as three magnitudes

lower than 24 hour germination counts for 18 month old

sclerotia. It is interesting to note that with the young

sclerotia, a stimulatory effect in germination is also seen

in treatments that were wet with the wheat leachate solution

(Table 5.3). Although germination counts were very low,

wheat leachate treated sclerotia germinated ten times

greater than the other two treatments at the 24 hour

counting period (Table 3). Germination trends at the 48

hour period are extremely difficult to explain with

germination from all treatments exceeding 70%. Both

distilled water and methanol/water treatments increased from

3% germination at 24 hours to 88 and 95% respectively.