Group Title: Quincy NFREC Research Report - University of Florida Research and Education Center ; NF-89-3
Title: Southern runner leafspot disease management, 1987-88
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 Material Information
Title: Southern runner leafspot disease management, 1987-88
Series Title: Quincy, NFREC research report
Physical Description: 4 p. : ill. ; 28 cm.
Language: English
Creator: Shokes, Frederick M ( Frederick Milton ), 1943-
Gorbet, Daniel W ( Daniel Wayne ), 1942-
Berger, D. A
North Florida Research and Education Center (Quincy, Fla.)
Publisher: North Florida Research and Education Center
Place of Publication: Quincy Fla
Publication Date: 1989
Subject: Peanuts -- Varieties -- Florida   ( lcsh )
Peanuts -- Diseases and pests -- Control -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: F.M. Shokes, D.W. Gorbet and D.A. Berger.
General Note: Caption title.
Funding: Research report (North Florida Research and Education Center (Quincy, Fla.)) ;
 Record Information
Bibliographic ID: UF00074380
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 85589788

Full Text

INort h.F10orLa Research and Education Center
------------- incy, Florida

Quincy, NFREC Research Report NF 89-3

F.M. Shokes, D.W. Gorbet and D.A. Berger

The late leafspot-resistant peanut variety, Southern Runner,
was planted at the Marianna Agricultural Research and Education
Center in 1987 and 1988 to test the effect of various management
programs on leafspot control and yield. Plots were six rows 20 ft
long planted on 3 ft centers. Standard management practices were
used for fertilization, insect control, and weed control according
to extension service recommendations. Gypsum was applied at
pegging and plots were irrigated as needed throughout both seasons
with a center pivot system. Leafspot-infested debris was sprinkled
on every sixth row early in the season to provide initial inoculum
to begin the leafspot epidemic. All plot rows were sprayed using
a tractor-mounted sprayer with a six-row boom equipped with three
hollow-cone (D3-45) nozzles per row. The experiment was arranged
in a randomized complete block split plot design. The fungicides
Bravo 720 (1.5 pt/A) and Spotless (0.125 lb/A) were main-plot
treatments. Bravo 720 is a 6 Ib/gal flowable formulation of the
protectant fungicide chlorothalonil. Spotless is a 25% wettable
powder formulation of the systemic sterol-inhibiting fungicide
diniconazole. Spray schedules were split-plot treatments arranged
in a scheme where zero represents an untreated check and the other
values represent the number of fungicide applications. The initial
application was made 40 days after planting and a 14-day interval
was used between applications.

1 2 3
1 2 3 4
1 2 3 4 5
1 2 3 4 5 6

1 2 3 4 5 6 7
2 3 4 5 6 7

3 4 5 6 7
4 5 6 7
5 6 7

6 7

There was also a delayed 21-day spray interval treatment in which
the first application was applied about 60 days after planting
allowing a total of four applications. Leafspot disease was
assessed five times during the season beginning in mid-August;

(Rhizoctonia solani) were assessed at digging. White mold was
assessed as hits per 40 row ft. Each hit is a focal point of
disease one ft or less in length. Limb rot was assessed as the
percentage of 40 row ft with symptoms of this disease. Rows 3 &
4 were harvested for pod yield measurements. Peanuts were
harvested 151 days after planting in 1987 and 155 days after
planting in 1988 with a modified commercial picker. Pod yield was
measured after drying pods to 10% moisture.

There was very little white mold or limb rot in the 1987 test
so no data was collected on these two diseases. In 1988 sufficient
levels of both diseases were present for evaluation. White mold
varied from 0-3.5 hits per 40 row ft in plots treated with Bravo
and from 0-0.5 hits in plots treated with Spotless. Most of these
results were not significantly different statistically (p.0.05) but
there was a trend toward more white mold in the plots treated with
the protectant fungicide Bravo. Limb rot varied from 0-36% in
plots treated with Bravo and from 0-17% in plots treated with
Spotless. Again trends were toward less limb rot in plots treated
with Spotless.

Pod yields of Southern Runner treated with Bravo ranged from
4018 Ib/A to 5280 lb/A when averaged over the two years. Yield of
peanuts treated with Spotless averaged slightly higher, 4495 lb/A
to 5722 lb/A. Figure 1 depicts the effect of the application
schedules on leafspot control for both fungicides. Only the
leafspot data for the last assessment is given.

Bravo 720 E Spotless






1-2 1-3 1-4 1-5 1-6 1-7 2-7 3-7 4-7 5-7 6-7 21D CK

Figure i. Effect of fungicide application
schedules in relation to leafspot control of
Southern Runner in 1987 and 1988. Ratings were
made using the Florida 1-10 scale.

Figure 2 depicts yield comparisons for the two fungicides. Pod
yields were generally higher when leafspot was less but the effect
was not nearly as great as the differences which would be expected
with a susceptible variety. With Bravo the last four



3000 I



1-2 1-3 1-4 1-5 1-6 1-7 2-7 3-7 4-7 5-7 6-7 21D CK

Bravo 720 E Spotless

Figure 2. Effect of fungicide application
schedules in relation to pod yield of Southern
Runner in 1987 and 1988.

applications of fungicide (4-7) were as effective as applying the
first five applications (1-5). The delayed 21-day schedule was
also as effective as these. With Spotless fungicide leafspot
control was as effective with the last three applications (3-5) as
with the first five (1-5) but yields were higher with the earlier
applications. This may indicate that with Southern Runner peanut
the growth regulator activity of Spotless fungicide may be as
important as the fungicidal activity in relation to yield. We
suspect that this is the case since disease control was negligible
when only three or four early sprays were applied (1-3 or 1-4) but
yields were still high. These sprays were applied during periods
of major vegetative growth. With Spotless as with Bravo the
delayed 21-day treatment was very effective.


Since the delayed 21-day treatment was effective with the two
fungicides over both years in maintaining disease at tolerable
levels and sustaining high pod yields this might be the treatment
of choice when growing Southern Runner peanut. This will result
in a savings of 3-4 fungicide sprays. Some disease will occur on
Southern Runner with this schedule and varying levels of
defoliation will be observed from year to year. After several
years of research with this resistant variety it seems likely that
disease levels and yield loss due to disease, will be maintained
at tolerable levels with a delayed 21-day schedule. This should
be true especially in peanuts in grower fields since no inoculum
will be applied to start an epidemic and the variety itself retards
the disease development. As with all good disease management it
will be important to have good crop rotation with non-host crops.
This will decrease the probability of having initial spore

Use of trade names does not constitute a guarantee or warranty
of products named and does not signify their approval to the
exclusion of other products of similar composition having
appropriate labels. Spotless fungicide has only been used
experimentally and is not yet available commercially.


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