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 Table of Contents
 Nitrogen efficiency study...
 Fertilizer demonstration plots
 Improving energy and water use...
 Potato variety development herbicide...
 Disease progress and influence...














Group Title: Field day activities (Agricultural Research and Education Center (Hastings, Fla.))
Title: Field day activities.
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Table of Contents
    Front Cover
        Front Cover
    Table of Contents
        Table of Contents
    Nitrogen efficiency study on potatoes
        Page 1
        Page 2
        Page 3
    Fertilizer demonstration plots
        Page 4
    Improving energy and water use efficiencies of seepage irrigation systems
        Page 5
        Page 6
    Potato variety development herbicide trial and growth regulatory test
        Page 7
        Page 8
        Page 9
    Disease progress and influence of early blight on tuber yields in nine potato cultivars during 1987
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
Full Text



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29TH F I E LD DAY AC T I V I T I E S


AGRICULTURAL RESEARCH AND EDUCATION CENTER


HASTINGS, FLORIDA


APRIL 14, 1988


Central Science
Library
MAR 28 199(
University of Florida


HASTINGS AREC RESEARCH REPORT HAS1988-1























PROGRAM 29TH FIELD DAY

AGRICULTURAL RESEARCH AND EDUCATION CENTER
Hastings, Florida

THURSDAY, APRIL 14, 1988, 1:00 PM

Presiding Jim Dilbeck, St. Johns County Extension Director


D. R. Hensel, Center Director, AREC Hastings Page
Welcome
Potato Outlook
Nitrogen Efficiency Studies 1
Ammonia Toxicity Study 3
Fertilizer Demonstration Plots 4

D. Z. Haman, Asst. Prof. Agricultural Engineering Dept.
Improving Energy and Water Use Efficiencies of Seepage 5
Irrigation Systems

J. R. Shumaker, Assoc. Prof., AREC Hastings
Potato Variety Development Trials 7
Herbicide Evaluation Studies 9

D. P. Weingartner, Assoc. Prof., AREC Hastings
Disease Progress and Influence of Early Blight on 10
Tuber Yields in Nine Potato Cultivars During 1987

Break

Tour of plots


Refreshments courtesy of ASGROW FLORIDA CO., SWIFT FARM CENTER,
HELENA CHEMICAL CO. and WISE FOODS.







Nitrogen Efficiency Study on Potatoes
D. R. Hensel, Center Director
S. J. Locascio, Professor, Vegetable Crops

This study was initiated in 1986 to determine the most efficient
combination of nitrogen rates, time of application and ratio of nitrate
needed for maximum yields. Nitrogen is generally the most expensive
ingredient in mixed fertilizer and is usually deficient in the sandy
flatwood soils of northeast Florida. Nitrogen is generally applied either
as nitrate (N03") or ammonical (NH4+) form. Most of the ammonical is
converted to NO3 form before uptake by potato roots. Since the cost of
N03-N tends to be more than NH4-N, one may consider applying nearly all
of the N as NH4, however, caution should be used to avoid NH4 toxicity.
Also, nitrogen can be leached by excessive rainfall and move into the
drainage waters which can also cause environmental concerns. Information
is needed to determine the most efficient utilization of N by potatoes
along with the corresponding yields. A factorial experiment which had
3 rates of N, 3 times of application and 3 ratios of NO3-N was designed.
Summary of the treatments follows:

Treatments Variables
N Rates 100, 200, and 300 Lbs/A.
N Application 0, 33, and 67% applied at planting
(Remainder at sidedressing)
N Form 5, 25, and 45% N03*N

In 1986, a positive linear and quadratic yield responses to all N
treatments were observed. Also a 3 way interaction existed for the three
main factors. This is shown in Table 1.







Table 1. Interaction of nitrogen rates, percent nitrogen in nitrate
form, and percent applied at planting on the total size A potatoes.
Spring 1986.

Nitrogen rates (lb./acre)z

100 200 300

% N at % NO3-N % NO3.N % N03-N

planting 5 25 45 5 25 45 5 25 45

cwt/A

0 145 131 159 176 175 158 212 197 195

33 203 231 206 275 254 286 291 295 279

67 211 233 238 246 337 311 186 330 336

z Interaction of rates, % N03-N, and % N applied at planting is
significant at 1% level.

Conclusions:
There was an interaction between the three factors studied and effect
of one cannot be summarized without considering the other two.

The yield response to N application peaked near 200 Ibs/A when most
of the N was applied at planting and 25% or more was in the NO3
form.

When high rates of NH4 (5% NO3 level) were applied at planting,
yield reductions were attributed to the excess ammonia. This was
also associated with much lower tuber set than just yield alone.

In 1987 after nearly 20 inches of rainfall, the only significant yield
differences were due to nitrogen rates. Therefore, this experiment is
repeated in 1988 to determine if the relationships detected in 1986 could
be duplicated.








Ammonia Toxicity Pilot Study on Potatoes
D. R. Hensel, Center Director


During 1986, the NO3 study showed that a possible ammonia toxicity existed.
A non-replicated pilot study was initiated to observe this effect more
closely. A 3x4x2 test was arranged with the following treatments:


Treatments


NH4-N

N03-N


.Variables


100, 200, and 300 Ibs/A

0, 25, 50, and 75 Ibs/A


Application


All at planting and 33% SD at 34 DAP


Plots will be observed for plant vigor and growth. Data will be taken
to determine what trends the treatments have on yield, tuber set, and
quality. This data along with the other NO3 study should help determine
what future studies are needed.


-3-








Fertilizer Demonstration Plots
D. R. Hensel, Center Director

Cooperators: G. Kidder, Assoc. Professor Soil Science
G. J. Hockmuth, Asst. Professor Vegetable Crops
J. D. Dilbeck, County Extension Director, St. Johns County
W. A. Tilton, County Extension Director, Putnam County
D. E. Schrader, County Extension director, Flagler County

This demonstration test is one of 4 experiments being conducted in the
tri-county area. The other 3 are on grower sites in each county. Each
test is site specific in that the basic application was determined by
soil test. Treatment 1 corresponds to the soil test recommendation. Then
four additional treatments were added to check out the validity of the
original recommendation. The last (Treatment 6) was to compare with the
grower practice at the site.

Treatments at the Hastings AREC are:

Treatments At Planting SD at 21 DAP SD at 42 DAP Total

1. 50-0-70 50-0-0 50-0-0 150-0-70

2. 50-0-0 50-0-0 50-0-0 150-0-0

3. 100-0-70 100-0-0 100-0-0 300-0-70

4. 75-0-70 75-0-0 75-0-0 225-0-70

5. 100-0-70 0-0-0 50-0-0 150-0-70

6. 132-33-99 0-0-0 80-25-80 212-58-179


Public is invited to observe these tests and compare the treatments. Yields
will be taken to determine differences among treatments. Each site has
been replicated 4 times in order to make valid statistical comparisons.








IMPROVING ENERGY AND WATER USE EFFICIENCIES
OF SEEPAGE IRRIGATION SYSTEMS


Dorota Z. Haman, Asst. Professor, Agricultural Engineering Department
University of Florida


Cooperators: Dale R. Hensel, Center Director, Hastings AREC
Allen G. Smajstrla, Prof., Agricultural Engr. Dept.
Fedro S. Zazuetta, Asst. Prof., Agricultural Engr. Dept.


Currently approximately 350,000 acres of vegetables, 120,000 acres
of citrus and 600,000 acres of pasture are irrigated by seepage irrigation
systems in Florida. These systems apply from 6 inches to more than 100
inches of water per year based on a survey by the US Geological Survey
(Duerr, A. D. and J. T. Trommer, 1982).

In seepage irrigation systems, runoff is unavoidable because a certain
depth of water is required in the water furrows to cause water to move
laterally to the center of the production beds, and gradients must exist
in the water furrows to provide drainage when rainfall is excessive. Thus
water flows continuously in the water furrows during irrigation and runoff
occurs from the lower end of the water furrows. Runoff from seepage
irrigated fields reduces irrigation efficiency. Efficiency of seepage
irrigation systems is often estimated to be 50% but it may range much lower
or higher depending on management, runoff, and other site-specific factors.
Through collection and recycling of runoff significant savings of water
can be achieved.

Recycling saves not only water but also energy. Pumping from a recycling
pond (or ditch) does not require as much energy as pumping from a deep
well because pumping lift is typically much less than that from a deep
well. As a result, significant savings in energy can be also achieved
during recycling.

The project at the Yelvington Research Farm demonstrates the functioning
and reliability of a water recycling and control system. The control system
has the advantage of being relatively low cost, so that in many cases its
cost can be recovered in the first year of operation. The system requires
a second pump for recycling of runoff water. However, because of the low
pumping lift, its pumping cost is less than that of the primary pump (deep
well), therefore the energy requirement for the operation of the recycling
pump is significantly smaller.

Construction of a collection ditch or pond at the site is necessary.
At the AREC Hastings site, another collection ditch was constructed just
to keep runoff water from this project separate. In most cases the existing
drainage ditch can be used. The recycling pump is placed inside the
collection structure and operates automatically when a float switch preset
for operation of the pump at a given water level closes.







Another major advantage of the system is significant reduction of pumping
from the aquifer. By using runoff water for irrigation, ground water pumping
is reduced, thus conserving a valuable natural resource, and reducing the
deterioration of water quality due to excessive pumping.

The recycling system resulted in significant savings of groundwater
pumped from the aquifer. In 1986, groundwater pumping was reduced by 46%.
The recycling process resulted also in total energy savings of 24%.

During the 1987 season, several unexpected events prevented the
collection of reliable data during much of the season. However, at the
end of the season after the irrigation system was repaired and properly
maintained, a savings of 45% of the groundwater and 20.5% of the energy
was demonstrated.

During the 1987 season water quality samples were collected from the
recycled and well water during the growth of a cover crop. Samples were
analyzed for total dissolved salts and nitrate concentration. No significant
deterioration of the water quality occurred during the recycling process.
The maximum concentration of salts in the recycled water did not exceed
1400 ppm which was approximately the concentration of the well water at
this site. Nitrogen was below 2 ppm in all samples. Water quality samples
collected were undoubtedly influenced by the low nitrogen application rate
(50 Ib. N/acre) used on the cover crop. The project will be continued
during the 1988 season. We are expecting to provide more information on
water quality of the recycled water.






Potato Variety Development
Herbicide Trial and Growth Regulatory Test
J. R. Shumaker, Assoc. Professor

I. Potato Variety and Seedling Evaluation

A. The Snack Food Association Test:

The Snack Food Association has sponsored regional potato chip trials
in 6 locations in the U.S. California, Pennsylvania, Michigan,
Red River Valley, Washington and Hastings, Florida. The trials
are designed to evaluate potential chip varieties for their
adaptability in terms of yield and size distribution, specific
gravity, and chip quality. For this test, 50 pound samples of
each clone were provided by the breeder. The trial is conducted
on a mini-commercial scale to simulate commercial cutting, handling
and planting of seed. The crop was planted on Feb. 4, and is now
70 days old. Following is a list of clones being currently evaluated
in Bed 16 OL.

Clone Clone Clone Clone
Atlantic (check) Norchip (check) AC 80545-1 MS 700-70
MS 700-83 MS 716-15 Saginaw Gold BR 7093-24
LA 0138 AF 236-1 WIS 855 NY 71
NY 72 NY 81

B. Advanced Replicated Intermediate and Observational Tests:

In these tests potato clones are evaluated in small plots (20 ft.)
in either advanced replicated tests (4 replications of each clone)
or observational and intermediate tests (1 or 2 replications of
each clone). Emphasis is placed on testing for superior yields,
quality and pest resistance. Data will be collected and evaluation
made of the following variables: vine types and vigor of the plants;
and tuber types, maturation, yields, specific gravity, chip color
and pest resistance. The tests were planted on Feb. 9 and 10 and
are currently 65 and 64 days old. Following is a list of the tests,
the number entries being evaluated and the location of each test.
A list of the clone entered in the Advanced Round White and Red
test is also included.

Test Entry Location
Advanced Round White or Red 59 Bed 7 NL Rows 5-16
Advanced Russet 18 Bed 18 OL Rows 3-10
Intermediate Russet 20 Bed 18 OL Rows 11-15
Intermediate Round White 24 Bed 17 OL Rows 2-7
Observational Round White and 54 Bed 17 OL Rows 8-15
Russet


-7-








Advanced Round White and Red Test:


Planting No.


Clone


Planting No.


Clone


Planting No.


B9792-157

B9792-158

B9792-16B

B0233-1

B0234-8

B0241-8

B0243-18

B0245-8

B0256-1

B9955-10

B0178-34

B0180-36

B0190-2

B0202-4

B0214-9

B0238-4

B0242-3

B0255-9

AF236-1

CS7232-4


AF845-11

AF875-16

AF875-17

Sunrise

New Norchip

New Superior

Denali 19

A129.69-1

TX9ND 1068 Red

LA 12-59 Red

Redsen "D" Red

TXA-17

LA-0138

NE 22.75-1

NEA 129.69-1

ND 1215-1

MS 700-83

NY 72

NY 71

NY 78


NY 81

WF 31-4

Denali

Shurchip

Saco

Delta Gold

FL 657

Campbell 13

Snowchip

B9792-8B

B0190-9

La Rouge Red

Sebago

Red La Soda Red

La Chipper

Superior

Atlantic

Ontario

Norchip


Clone








II. Herbicide Evaluation in Commercial Potato Production


The use of either Lexone or Sencor has been an effective tool in
providing annual grass and broadleaf weed control in Hastings potato
fields for more than 15 years. Under normal weather conditions when
these chemicals are applied preemergent to the crop and at their
recommended rates (0.5-0.75 lb ai/A) early crop injury is either minimal
or not observed. However, due to rainfall and the critical low
temperatures of March 17, early crop injury was considered moderate
but extended throughout the area on most varieties.

Six preemergent herbicide treatments are currently being evaluated
on Atlantic potatoes. The crop was planted on Feb. 10 and is now
64 days old. The herbicide treatments were applied on March 4 and
are presented below.

Treatment Rate
lb ai/A
Turbo 8E (6.55 Ib ai Dual + 1.45 lb ai Sencor) 2.0
Dual 8E 1.64
Sencor 4F 0.5
Sencor 4F 0.36
Check Hoed
Check Unhoed







Disease Progress and Influence of Early Blight
on Tuber Yields in Nine Potato Cultivars During 1987.
D. P. Weingartner, Assoc. Professor

Late blight (Phytophthora infestans) and early blight (Solanum solani)
have been the two most important foliage diseases affecting potatoes
in northeast Florida (NEF) since the late 1800's when the crop was
first grown in the area. Weather conditions in NEF usually favor
late blight during March-mid April. Early blight generally occurs
later in the season both because weather conditions are more favorable
then and because it is a disease of senescence, attacking
"physiologically old" tissue.

The relative impact of late blight on potato production in NEF has
changed dramatically through the years. A loss of 25-30% of the crop
was reported in 1903 (5). The disease was classified as moderate
(1-4% losses) to severe (8-15% losses) 15 seasons of 18 during 1931-1949
(10). Since 1950, however, there have been only 4 moderate and 0
severe outbreaks of the disease in NEF.

Diminished importance of late blight in NEF can be attributed to a
number of factors: reduced levels of introduced inoculum in seed due
to seed certification and requirements of the Florida Seed Law; planting
of cultivars with horizontal or rate reducing resistance; availability
of highly effective fungicides beginning with the ethylene
bisdithiocarbamates during the mid 1940's; and, grower awareness
together with maintenance of effective fungicide programs (some of
which has been due to late blight spray advisories based on forecasting
methods).

The situation with early blight is nearly the opposite. Opinions
of Florida pathologists regarding importance of early blight in potatoes
have varied through the years. Sherbakoff (7) and Weber (8) both
attributed highly significant losses to early blight. Eddins (1,2,3)
on the other hand stated that early -blight, although a problem- in
south Florida, did not seriously affect potato production in NEF.
During 1981-84 I presented data from replicated experiments illustrating
that early blight, during some seasons, indeed, causes significant
losses (9,11). The previously unpublished data in Table 1 are typical
of these observations.

During the past several seasons, foliage disease research at this
AREC has focused on early blight. The general objectives of these
efforts have been to: i) quantify magnitude of losses due to early
blight in several different potato cultivars; ii) identify other
potential pathogens in early dying such as Alternaria tenuis (=
Alternata alternate); and iii) identify critical spray periods based
on crop phenology, and other factors.

A portion of the data from 1987 is presented in this report.


-10-







METHODS


The experiment was planted 18 Feb. A split plot test design was used.
Main plots consisting of three fungicide programs (Ridomil 2E at 1.0
pt/acre to control late blight, but not early blight; Bravo 500 at
1.125 pt/acre to control late blight and early blight; and nonsprayed
to allow both diseases to develop) were replicated four times. Potato
cultivars Atlantic, Sebago, Ontario, Superior, New Superior, La Chipper,
Red La Soda, La Rouge, and Green Mountain were planted as subplots.
Cultivar selection was based on one or more of the following criteria:
whether it is planted in NEF; its maturity class (ie early-late);
and on availability of literature from other potato producing areas
describing development of early blight in the particular cultivar.
Sub plots were four rows wide and 25 feet in length. The first
fungicide application was made 14 April. Ridomil was applied every
14 d for a total of four applications and Bravo 500 every seven days
for a total of eight. The crop was harvested 8 June. Data were taken
in the center two rows of each plot. Early blight and defoliation
were estimated- at three locations in each plot using the 1-12
Horsfall-Barratt (4) rating system. Data were converted to percentages
using the Eli Lilly conversion tables (6). Data were subjected to
regression analysis using tuber yields as the dependent and foliage
disease as the independent variables, respectively.


Results and Discussion

It is important to note that these data are based on one season's
observations and that development of early blight, even in a single
cultivar, can vary considerably from season to season.

The first early blight lesion was observed in the experiment 20 April.
Although less than 0.5% disease was observed in the most severely
affected plots by 29 April, considerable spread had occurred as
evidenced by presence of one or more lesions in 67 of the 108 plots
in the study. These data were not used in the analysis of disease
progress.

There was considerable variation in percentage early blight among
cultivars by 12 May (Table 3). The apparent infection rates among
cultivars between 12 May and 26 May were, surprisingly, fairly uniform,
with the lowest values being associated with those cultivars having
the greatest percentage early blight on 12 May.

One difficulty in following disease progress of early blight is that
other factors such as heat stress, wilt diseases, and possibly other
foliage pathogens such as Botrytis sp. and Alternaria spp (9) can
contribute to defoliation as the potato plants senesce. For this
reason both an early blight rating, based on presence of early blight
lesions, and a total defoliation or foliage loss rating were taken
during the season. An example of the relationship of early blight
to defoliation is illustrated in Table 4. Both early blight and
defoliation vary among cultivars with percentage defoliation tending
to be greater than that of early blight. A comparison of early blight
and defoliation in sprayed and non sprayed plots is shown in Table
5.


-11-






The rationale being used in this study is to follow, on a regular
basis, the progress of early blight and total defoliation in the crop
and to relate these data to tuber yields and specific gravity. Use
of regression analysis and calculations of coefficients of determination
(R ) presumedly will estimate the most critical time to control early
blight and defoliation among the different cultivars. That is,
fungicides to control early2 blight should be applied before the
occurrence of the maximum R value. In other cases, absence of a
significant R value would indicate that control of early blight and/or
defoliation was not a critical factor in maximizing yields and specific
gravity.

The R2 values shown in Table 5 are the maximum values calculated during
the season. Data suggest that early blight was not a major factor
affecting yields in Sebago, Superior, or Red La Soda. On the other
hand, more than 60% of the variation in yield in Atlantic and Green
Mountain was associated with early blight. Based on these data, maximum
yields during 1987 would have been associated with early blight control
before 18 May in Atlantic and 6 June in Green Mountain.

In summary, important observations made during 1987 included: a) as
expected, severity of early blight on a given date varied among potato
cultivars; b) disease progress of early blight among cultivars was
relatively uniform; c) cultivars may play an important role in
determining reliable and profitable timing of fungicide applications
to control early blight; d) the relative importance of early blight
in relationship to yields varies among cultivars.

Future research will relate disease progress of early blight to degree
growing days or physiological days and to tuber bulking among the
several potato cultivars.

Literature Cited

1. Eddins, A. H. 1948. Incidence of potato diseases at Hastings,
Florida in 1948. Plant Disease Reporter 32:302-303.

2. Eddins, A. H. 1943. Potato diseases in the Hastings section of
Florida this season. Plant Disease Reporter 27:204-241.

3. Eddins, A. H. 1938. Losses caused by potato diseases in the
Hastings section, Florida. Plant Disease Reporter 22:272-274.

4. Horsfall, J. G. and R. W. Barratt. 1945. An improved grading system
for measuring plant disease. Phytopathology 35:655.

5. Hume, Harold. 1904. Potato Diseases. Fla. Agr. Exp. Sta. Bull.
75:181-199.

6. Redman, C. E., E. P. King, I. F. Brown, Jr. Tables for converting
Barratt and Horsfall rating scores to estimated mean percentages.
Eli Lilly and Company. 110 pp.


-12-







7. Sherbakoff, C. D. 1917. Some important diseases of truck crops
in Florida. Fla. Agr. Exp. Sta. Bull. 139. pp 193-277.

8. Weber, G. F. 1923. Potato diseases and insects. Fla. Agr. Exp.
Sta. Bull. pp 102-164.

9. Weingartner, D. P. 1984. Evaluation of new and traditional
fungicides for control of late and early blight diseases in
northeast Florida potatoes. Proc. Soil and Crop Sci. Soc. Florida.
43:150-153.

IO. Weingartner, D. P. 1982. Lessons learned from the potato late
blight epidemic of 1982. Proc. Florida State Hort. Soc. 95:308-312.

11. Weingartner, D. P. 1981. Managing foliage diseases of potatoes.
Hastings Research Report PR 1981-4. 7 pp.


-13-








Table 1. Percentage early blight, defoliation and yield of US Size A
tubers in Atlantic cultivar potatoes during 1982.


Percentage


early blight


% defoliation


Yield size ..-.
A tubers


5/7 5/17 5/7


5/17


Fungicide 4.1 a 32.0 6.4 48.4 a 161 a

No Fungicide 18.8 b 34.4 9.4 95.3 b 138 b


Values with a
significantly


column followed by the same letter do not vary
(P=.05). Lack of letter denotes nonsignificance.


Table 2. Effect of fungicide schedules on percentage early
blight percentage defoliation and potato yields.
1987 Epidemiology Experiment. .

Fungicide Early blight Defoliation Size A
program/ 5/18/87 5/21/87 tubers2/
% % cwt/acre
Ridomil 2E 43.9 73.9 112
Bravo 500 17.8 20.4 137
Nonsprayed 44.0 74.7 110

1/ Ridomil 2E applied at 1.0 pint/acre every two weeks;
Bravo 500 applied at 1.125 pints/acre on a 7-day schedule.
2/ Averaged across nine potato cultivars.


-14-


Treatment







Table 3. Percentage early blight and apparent infection rates
of early blight in nine potato cultivar during 1987.

% E. Blightl/
r 2/
Cultivar 5/12 5/18 5/21 5/26 Value

Atlantic 2.6 19.5 45.6 64.3 .29

Sebago 2.6 16.0 33.1 41.6 .23

Ontario 3.5 5.7 11.4 20.0 .17

Superior 6.4 40.4 65.7 68.9 .25

New Superior 4.3 29.7 59.2 60.2 .26

La Chipper 14.6 44.5 64.9 58.4 .15

Red La Soda 8.4 31.0 62.0 59.7 .20

La Rouge 8.7 41.7 64.5 70.1 .23

Green Mountain 7.6 30.3 45.9 51.6 .18

1/ The first early blight lesion was observed 20 April. By
29 April the percentage in the most severely affected plots
was still < 1%.

2/ Apparent infection rate (r-value) calculated as follows:

1 X2 X1
r [In ( ) In ( )]
bt 1-42 1-X1

Where
r = apparent infection rate
X1 and X2 = proportion disease-on-12-May and 26 May, respectively
St = No. days between observations


-15-









Table 4. Percentage early blight and defoliation observed in nine
potato cultivars during 1987.

Potato Percentage2/
cultivarl/ Early blight 5/18/87 Defoliation 5/21/87

Atlantic 27.1 d 50.4 c
Sebago 27.3 cd 38.9 d
Ontario 7.0 e 15.6 e
Superior 52.1 a 77.7 a
New Superior 40.5 b 66.4 b
La Chipper 48.8 a 71.6 d
Red La Soda 40.1 b 66.9 b
La Rouge 47.4 ab 69.5 b
Green Mountain 26.9 d 49.7 d
1/ Cultivar dates are means of three fungicide programs.

2/ Values within a column followed by the same letter do not
vary significantly (P=.05) via Duncan's Multiple Range
Test.


-16-





Table 5. Percentage early blight, percentage defoliation, yield Size A tubers and maximum R2 values in nine different
potato cultivars during 1987.

% Early blight1'2/ % defoliation1'2/ Yield size
5/18/87 5/21/87 A-tubers Maximum R2 values3/
No No No Early blight Defoliation
Cultivar Fungicide fungicide Fungicide fungicide Fungicide fungicide
Atlantic 12.5 32.6 xx 16.4 64.5 xxxx 176 96 xx 61.3 xx (5/18) 64.4 xx (5/18)

Sebago 16.0 35.4 x 12.5 53.8 xxx 106 92 NS 0.0 NS 36.7 x (5/18)

Ontario 5.3 8.2 x 7.8 20.2 xx 162 144 NS 22.5 xx (5/26) 18.5 NS (5/21)

Superior 24.0 66.9 xxx 38.3 95.8 xxx 77 69 NS 14.9 NS (5/18) 16.9 NS (5/18)

New Superior 23.5 49.1 xxxx 23.9 87.1 xxxx 153 123 xx 45.1 xx (5/18) 46.6 xx (5/18)

La Chipper 18.0 61.5 xxxx 25.8 95.1 xxxx 96 78 xx 36.7 x (5/18) 34.7 x (5/21)

Red La Soda 27.2 43.7 xxx 25.1 86.2 xxxx 150 134 xxxx 0.0 NS 18.5 NS (5/29)

La Rouge 23.5 63.3 xxx 19.6 95.9 xxxx 129 113 NS 34.9 x (6/2) 18.5 NS (4/29)

Green Mountain 10.2 35.6 xxxx 13.9 71.9 xxxx 188 135 xx 61.7 xx (6/6) 61.7 xx (6/2)

Means 17.8 44.0 20.4 74.7 137 110


Early blight and defoliation were rated
using the Eli Lilly Conversion Tables.


using the 1-12 Horsfall Barratt Scale. Ratings were converted to percentages


c/ Fungicide no fungicide comparisons within each cultivar were subjected to t-test analysis. Probability ranges are
indicated by asterisks as follows: x = .10-.20; xx .05-.10; xxx = .01-.05; xxxx = .001-.01
3/ R2 values (coefficients of determination) were calculated using yields of size A tubers as the dependent and percentage
early blight or defoliation or the independent variables, respectively. As expressed here, the R value essentially
estimates the percentage of the differences in yield of size A tubers which can be ascribed to the percentage early
blight or defoliation on the observation date shown. ( ) indicates observation date. Asterisks indicate probability
level as follows: x = .05; xx .01.


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