Group Title: Research report (North Florida Research and Education Center (Quincy, Fla.))
Title: Peanut plant pathology
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Permanent Link: http://ufdc.ufl.edu/UF00066144/00001
 Material Information
Title: Peanut plant pathology
Series Title: Research report (North Florida Research and Education Center (Quincy, Fla.))
Physical Description: 10 leaves : ; 28 cm.
Language: English
Creator: Shokes, Frederick M ( Frederick Milton ), 1943-
North Florida Research and Education Center (Quincy, Fla.)
Publisher: North Florida Research and Education Center
Place of Publication: Quincy Fla
Publication Date: 1997
 Subjects
Subject: Peanuts   ( lcsh )
Pathology   ( lcsh )
Genre: non-fiction   ( marcgt )
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Statement of Responsibility: F. M. Shokes.
General Note: Caption title.
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Bibliographic ID: UF00066144
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 71196097

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Marston Science
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_/// JAN 2 6 1998
N 2 998 Research Report NF-97-7
University of Florida
Peanut Plant Pathology

F. M. Shokes

The goal of the plant pathology program on peanut at the North Florida Research and Education
Center (NFREC) at Quincy and Marianna, is to develop disease management programs that are
economically sustainable. Research includes evaluation of cultivars for resistance to the most
important diseases of peanut in north Florida. These include early and late leaf spot diseases, stem
rot (white mold), and spotted wilt virus. Cultivars and breeding lines developed by Dr. D. W. Gorbet
are tested using methods developed at the NFREC as well as in neighboring states. Peanut
genotypes are grown in small plots under good growing conditions (typically good conditions for
disease). This research also entails evaluating various fungicidal and biological control methods in
an effort to integrate these into management schemes. In addition to these we develop disease
forecasting models in an attempt to find better ways to control diseases with fewer inputs. The
diseases and disease responses that are frequently evaluated are summarized below.

Leaf spot Diseases Leaf diseases are evaluated under natural pressure from local spore inoculum.
The inoculum pressure is typically higher than in most peanut fields due to the presence of
unprotected check plots and/or spreader rows. This insures that all plants have a good chance to be
exposed to the fungal pathogens and minimizes the potential for disease escape. These conditions
result in a hard test for the plants, fungicide, or practice that is under evaluation. Plots are evaluated
using the Florida 1-10 scale. This is a widely used assessment system that was developed at the
Marianna, NFREC. Using this method a one represents a healthy plant and a ten represents plants
that are totally covered with leaf spot, defoliated, and dead or dying. When you observe a low
number (<4.0) for leaf spot on the tables included in the following tests that is indicative of a
treatment or genotype that did well.

Stem Rot The fungus Sclerolimn rol/sii causes the disease known as stem rot (frequently called
white mold). This disease is somewhat erratic unless inoculation is used. We generally inoculate the
tests for resistance of peanut to this disease in order to minimize the number of escapes. The
inoculum is pretested for pathogenicity, then grown on sterile oat seed and applied to plots with a
specified watering regime to insure infection. This system puts plants under much higher pressure
than would normally be encountered in most fields. We sometimes conduct fungicide tests without
inoculating plants if peanut has been grown in the test area and natural inoculum is known to be
present. This more nearly represents natural inoculum pressure.
Usually fungicide tests include leaf spot and stem rot evaluations since we are dealing with
management systems that must address both problems. Stem rot is typically evaluated at digging
when plants are inverted in windows. Stem rot damage is readily seen on recently inverted plants
and is assessed as the number of hits/40 row feet, then converted to % stem rot. To determine
whether a genotype has good resistance or a treatment works well, the % severity must be compared









to appropriate checks since stem rot is seldom completely eliminated.

Limb Rot The fungus Rhi.octonia solani frequently causes a disease of the lateral branches of
peanut that begins out from the center of the plants and progresses toward the main stems. This
disease does not occur every year in every field. It does occur when conditions are wet and slightly
cooler than normal. It is worse on rows where field traffic occurs causing vine injury. This disease
is assessed when it occurs but we do not inoculate to increase limb rot. We assess limb rot as the
percentage of lateral branches affected by the disease within a plot.

Spotted Wilt Virus (TSWV) Spotted wilt virus is carried to peanut by adult thrips that acquired
the virus by feeding on an infected plant while in the juvenile stage. If infection occurs this virus
causes severe stunting of plants and decreases yield significantly. Later infections may not always be
noticed until the late pod development stage when plants turn very yellow. When testing for spotted
wilt resistance spreader rows of a highly susceptible cultivar can be used to increase the disease
probability and uniformity. We typically do not inoculate but rely on the natural occurrence of this
disease. Spotted wilt is assessed when it occurs as % incidence (the percentage of plants showing
symptoms) and % severity (the percentage of plants with severe symptoms). Unfortunately this
disease has become so prevalent that it must be accounted for in every test.

Rust Peanut rust is a disease that is sporadic in occurrence in north Florida but can become a factor
when cool wet conditions occur earlier than normal in the growing season. Rust causes little orange
pustules on leaves and as it spreads causes plants to die. It occurs in distinct focal points in fields and
spreads out from these points. Plants heavily infected with rust will turn black and retain their leaves
as they die. We typically assess rust using a 0-4 scale in which zero represents healthy plants and a
four represents plants killed by rust.

Plant Pathology Aspects of the Peanut Cultivar Development Program at the North Florida
Research and Education Center Numerous tests are conducted annually to determine the
response of peanut breeding lines to disease. Every year we can depend on the occurrence of leaf
spot diseases, spotted wilt virus, and stem rot (white mold). In some tests we inoculate to ensure
that stem rot occurs but this is unnecessary for leaf spot diseases or spotted wilt. Some years we also
have limb rot and/or rust and can evaluate the response to these diseases. Considerable time has been
spent researching ways to effectively evaluate these diseases, inoculate with appropriate pathogens,
and test the plant responses. In some tests we are concerned mainly with diseases caused by
soilborne pathogens. In such tests leaf spot is controlled with frequent applications of a foliar
fungicide (this was the case in the test presented in Table I). Controls such as the susceptible cultivar
Florunner and the partially-resistant cultivar Southern Runner have been included for comparison.

We compared 32 breeding lines for their response to stem rot. Plots were inoculated with the
fungus so the probability of any given plant getting the disease was very high in the test (>60%). The
breeding lines tested ranged from having slightly less, to having 66% less, stem rot than susceptible
Florunner. Since Florunner had a 61% incidence of disease (61% of the plants had stem rot), then
any line having less than 40% incidence was significantly better. Some lines may have a relatively


I I









high incidence of stem rot but still yield well. This may be due to a tolerance for the disease or some
mechanism for resistance that keeps the disease from severely affecting the plant.

In some cases the effects of one disease can mask the effects of another. For example, if a
particular line has a high level of stem rot then limb rot is difficult to determine because the symptoms
are masked by the other disease. Limb rot which is caused by Rhizoctonia solani, also tends to be
highly variable in small plots. This disease occurs on the lateral branches from the between-row
middles back toward the row centers and is thus affected by traffic patterns of all in-field operations.
Limb rot data is included in the table but is very variable. When limb rot and stem rot levels are low
(less than 35 and 15%, respectively) the line has some potential to minimize the effects of these
diseases.

Spotted wilt virus is transmitted by thrips and we rely on natural infection for evaluation of
plant responses. In some tests highly susceptible spreader rows are used to enhance the probability
of disease and to decrease the probability of plants just escaping the disease. No spreader rows were
used in the test shown in Table I but disease incidence was very high throughout the test. Some
breeding lines held up well and had significantly fewer plants with virus symptoms than Florunner.
Some had more. In some cases, as with stem rot, the virus incidence may be high but the severity
may be minimal having little effect on yield. Plant genetics, such as were compared in this test is but
one important factor in the minimization of spotted wilt. Spotted wilt virus is affected by other
factors such as planting date (early, mid, or late), within-row spacing, and insecticide used.

To fully appreciate the value of such lines consider the results from a few entries in this test.
For example, UF91108 had 23% spotted wilt virus, 31% stem rot (significantly less than Florunner),
and 14% limb rot and yet it produced 4106 lb/A pod yield compared to 1725 lb/A for Florunner. The
line 87x8-2-1-1 had 29% spotted wilt virus, only 8% limb rot, and 28% stem rot and produced 5153
Ib/A of pods. Line 86x45B-10-1 had 40% spotted wilt virus, 12% limb rot, and 28% stem rot and
a yield of 4915 Ib/A. This was a replicated test so these values represent an average over four
replicate plots.

You can readily see that there is a great deal of difference between these lines and the
susceptible control and varying degrees of difference among the lines themselves. It takes many tests
such as this across years and locations to determine the full value of any breeding line. The real value
of partial resistance can only be realized when a line is placed in large plantings under more normal
conditions (pathogen populations, etc.). It must be stressed that partially resistant cultivars do get
disease. They will just get less than would a susceptible cultivar under the same conditions. Multiple
other factors also go into the process of picking a potential winner to become a cultivar. Just a few
of these factors are the ability to produce consistently high grade pods, taste, and chemical quality.












Table 1 Comparison of disease resistance on peanut breeding lines in 1996


Gcnotvpc
UF91108
84x47-10-1-1-1
84x47-1
84x9A-1
79x4-6
84x47-10-1-1-3
84x14-2
84x49-8-2
84x49-8-1
79x4-6-2-1-1
79x4-6-2-1-3
84x9A-3-I
84x28-5-1
84x23-1-2
84x9B-1-1-1
84x9B-4-2
86x45A- 12
81206-2-21
81206-2-24
86xl0A-6-2
86x10A-I 1-1
84x47-10-1-1-2
84x9B-4-2-1
84x 19-5-1
84x6-9-1 -1
87x8-2-I-1
86x43-4-2
86x52-6
84x28-5-4-1
86x45B-10-1
84x28-5-5
84x38-4-1-1
Southern Runner
Florunncr


LSD.05 0.8 11.2 21 660
*Plots were inoculated with Sclerotium rolfsii and chlorothalonil was applied seven times at
1.5pt/A to control foliar diseases.


% TSWV % Limb Rot
23 14
15 8
20 15
18 17
12 6
19 15
22 14
36 20
38 22
21 13
16 8
34 19
28 25
33 15
22 12
9 3
20 9
37 26
36 38
42 17
35 15
10 15
18 5
41 5
38 4
29 8
18 20
48 19
29 7
40 12
29 17
50 35
21 7
33 9


% Stem Rot
31
33
24
25
25
31
47
52
25
34
30
53
53
48
53
32
30
33,
27
65
65
42
44
49
50
28
49
33
22
28
26
48
42
61


Pod Yield (Lb/A)
4106
4078
4574
4026
4089
4385
3451
3031
3959
4026
3606
3041
3336
3030
3792
3965
4718
3930
4109
2847
2594
3859
3905
2553
2827
5153
3764
2814
4346
4915
3629
3076
3107
1725









Control of Peanut Leaf Spot and Stem Rot With Fungicides The peanut cultivar
Andru 93 was planted in Dothan fine sandy loam soil (pH 6.1) at the North Florida Research and
Education Center, Quincy, on 10 May 1996. Plots were four rows, 20 ft long, planted on 3 ft
centers, with 4 seed per row ft. Treatments were applied to the center two rows of each plot only
and outer rows were used as spreaders. Plots were arranged in a randomized complete block design
with fungicide treatments as the variable. Plots were fertilized with 500 lb/A of 3-9-18 prior to
planting and 1000 Ib/A of gypsum was applied on 23 Jul to supply additional calcium in the pegging
zone. The insecticide Thimet 15G (6 Ib/A) was applied at planting for thrips control and Asana at
3 oz/A was applied on 1 Aug for control of leaf hoppers. Weeds were controlled at planting using
2 pt/A of Prowl plus I pt/A of Dual, followed by I 1 oz/A of Gramoxone plus 1 pt/A of Basagran on
28 days after emergence. Rainfall was adequate for crop growth and disease development with 1.4,
2.5, 6.2, 6.5, and 7.6 in. in May, Jun, Jul, Aug, and Sep, respectively. Fungicides were applied to the
plots using a CO,-powered backpack sprayer equipped with a 2-row boom with three 8001 flat fan
nozzles per row at 2.5 mph and 40 psi. Fungicides were applied seven times on 14 Jun, 27 Jun, 13
Jul, 25 Jul, 5 Aug, 16 Aug, and 29 Aug. Plots were inverted on 16 Sep, 129 days after planting.
Combining was delayed until 23 Aug because of inclement weather. The crop was subjected to four
rain events before it could be harvested. Leaf spot assessments were made periodically during the
season using the Florida 1-10 scale in which a one represents healthy plants and a 10 represents plants
completely defoliated by leaf spot diseases.

The predominant leaf spot disease by the end of the season was late leaf spot, representing
96% of the lesions present. Stem rot was assessed as hits per 40 row ft at inversion and converted
to the percentage of row ft with one or more disease loci. The percentage limb rot was assessed at
inversion but numbers were typically very low, highly variable, and apparently affected more by traffic
than by fungicide application. The lowest leaf spot ratings were achieved with SAN619F tank-mixed
with chlorothalonil at 4.2 or 7.3 oz/A for seven and four (3-6 block) applications, respectively.
Folicur plus Induce applied at 7.2 oz/A in a 4-spray block (applications 3-6) with Bravo Weather Stik
(applications 1,2, and 7; 1.5 pt/A) controlled leaf spot diseases and stem rot better than Folicur at 4.1
oz/A tank-mixed with 0.75 pt/A of Bravo. Bravo Weather Stik at 1.5 pt/A plus Moncut at 0.6 lb/A
was similar to the 4-spray block of Folicur and a 4-spray block of SAN619F at 7.3 oz/A for control
of stem rot. Yields were adversely affected by inclement weather when drying in windows.









Table 2 Comparison of fungicides for management of leaf spot and stem rot diseases in .996.

Final Percent Pod
Ircalmnclt naml; ;ie ad ratleA
treatment ae nd e'A Schedule leaf AUDRC Stemrot Yield
spot lb/A
Check 9.8 382 /.5 /31
Bravo VWather Stik 6 F 1.5 pt. .......................... 1 7 4.5 178 20.8 2543
Bravo Weather Stik 6 F 1.5 pt. 1 7
Lorsban 15 G 13.3 lb ................... ............ 60 da 4.6 196 13.8 2712
Bravo Weather Stik 6 F 1.5 pt. 2, 7
Folicur 3.6 F7.2 (11oz)- Induce .06" vv ................ 6 3. 7 141 5.6 3337
1ravo Weather Stik 6 F 1.5 pt. 1, 2, & 7
Folicur 3.6 F 7.2 (11 oz) Induce .06". v.v 3 6
l.orsban 15 ( 13.3 Ib ... .. .......... .. ... 60 day 3.6 109 11.9 3003
Bravo Weather Stik 6 FI 1.5 pt. 1,2,5,6,7
Folicur 3.6 F 7.2 (11 o/.) Induce .0)6" v.v ... ..... 3,4 4.4 161 26.2 2351
3Brvo Weather Stik 6 F 1.5 pt. 1,2,5,6,7
Folicur 3.6 1:7.2 (11 on) Induce 06". v v 3,4
Lorsban 15 ; 13.3 1b ................ ......... ... 60 day 4.2 128 16.2 2745
Bravo Weather Stik 61- 1.0 pi. .Till 3.6 LC 2.0 (11 oz) ..... I 7 4.2 131 33.1 2653
Bravo Weather Slik 6 1F 1.0 pt.. Tilt 3 6 EC 2.0 (11 o/) 1, 2, 7
Folicur 3.6 F 7.2 (11 o/.) 13rao Weather Stk 6 1 .5 pt. .. ... 3 6 3.0 93 17.5 3410
Bravo Weather Stik 6 F 1.5 pt. 1, 2, 7
Moncut 50 WP .6 lb B:ivo Weather Stik 6 1- 1.5 l .. 3 6 4.5 176 7.5 2996
B1ravo Weather Stik 6 F 1.0 pt.- Tilt 3.6 EC 2.0 (11 oz) 7, 2, 4, 6,
Moncut 50 WP 6 1h ravo \Wathcr Slik 6 1:1.5 p .. 3, 5 4.7 164 14.4 2733
Echo7206 F1.pl ..... ... .... .. 7 4.8 166 25.6 2275
l-:nsin 720 1 5 pt 7 4.9 182 16.9 2795
Terranil 6L .5 pt ................................ I 7 4 .9 194 26.9 2 113
Terranil60 DIF 1.25 Ih .... ..... ..... 7 4.7 195 19.4 2473
Bravo Wcalhcr Slik 61 .75 pl SAN619F 2 67 SC 2 6 ((11 o).. 7 2.6 72 9.3 3244
Bravo Weather Stik 6F .75 plt SAN619F 2.67 SC 4-.2 (11 oz).. 7 1.9 44 6.9 3628
Bravo Weather Stik 61 1.5 pit 2, 7
SAN619F 2.67 SC 7.3 (11 oz) ......................... 3 6 2.0 67 3.8 3779
Bravo Weather Stik 6F.75 pl Folicur 3.6 F I (1 oz) .. 7 4.2 132 13.1 3157
li) P< .05 .56 33 8.7 794

'Schedules were seven sprays (1-7) applied on 2-wk intervals beginning 34 days after planting.
2Final leaf spot ratings were made on 19 Sep using the Florida 1-10 scale in which a 1 represents
healthy plants and a 10 represents plants
killed by leaf spot.
'AUDRC represents the area under the leaf spot rating curve.









Leaf Spot and Stem Rot Management in Peanut Using Fungicides The peanut
cultivar Andru 93 was planted in Dothan fine sandy loam soil (pH 6.1) at the North Florida Research
and Education Center, Quincy, on 17 May 1997. Plots were four rows, 20 ft long, planted on 3 ft
centers, with 4 seed per row ft. Treatments were applied to the center two rows of each plot only
and outer rows were used as spreaders. Plots were arranged in a randomized complete block design
with fungicide treatments as the variable. Plots were fertilized with 500 lb/A of 3-9-18 prior to
planting and 1000 lb/A of gypsum was applied on 23 Jul to supply additional calcium in the pegging
zone. The insecticide Thimet 15G (6 Ib/A) was applied at planting for thrips control and Asana (3
oz/A) was applied on 1 Aug for control of leaf hoppers. Weeds were controlled at planting using 2
pt/A of Prowl plus 1 pt/A of Dual, followed by 1 I oz/A ofGramoxone plus 1 pt/A ofBasagran on
28 days after emergence. Rainfall was adequate for crop growth and disease development with 1.4,
2.5, 6.2, 6.5, and 7.6 in. in May, Jun, Jul, Aug, and Sep, respectively. Fungicides were applied to the
plots using a CO,-powered backpack sprayer equipped with a 2-row boom with three 8001 flat fan
nozzles per row at 2.5 mph and 40 psi. Fungicides were applied seven times on 17 Jun, 1 Jul, 17 Jul,
31 Jul, 14 Aug, 28 Aug, and 9 Sep. Plots were inverted on 23 Sep, 129 days after planting and
picked on 26 Sep. Leaf spot assessments were made periodically during the season using the Florida
1-10 scale in which a one represents healthy plants and a 10 represents plants completely defoliated
by leaf spot diseases. Stem rot was assessed as hits per 40 row ft at inversion and converted to the
percentage of row ft with one or more disease loci.

The predominant leaf spot disease near the end of the season was early leaf spot. The
percentage limb rot was assessed at inversion but numbers were too low to be of consequence. The
lowest leaf spot ratings were achieved when the systemic fungicide Folicur was used as a block
treatment or in a tank mix with other fungicides. The incidence of stem rot in the plot area was
relatively low and Folicur, Abound, Moncut and the IB... products typically did well in minimizing
this disease. The tospovirus, TSWV, was present in significant incidence but symptom development
occurred too late in the season to be a yield determinant. Yields were high, ranging from 1170 Ib/A
for the check to 4637 Ib/A for one treatment which included a 6-spray mix of Folicur at 4.8 oz/A and
Abound at 0.1 lb ai/A. Of the IB... treatments IB 11924 worked best against stem rot in a 4-spray
block of applications (3-6). Whereas IB16311 at 1% v/v plus Abound at 0.3 Ib ai/A worked well
against stem rot and allowed high yields (4484 lb/A).












Table 3 Fungicides and fungicide schedules tested for leaf spot and stem rot management in 1996.
Treatment name. ralc. A Spray Final Percent pod yield
schedule' Leafspotl AUDRC' Stemrot lb/A


U ntrcatcd C heck ........ ... .. .. .. ...
Bravo W eaher Sik 6 1.5 p .............. ... ......................
Echo 720 6: 1.5 pt
Folicur 3.61 7.2 11 o/ Induce 1.6". v ... ........
B1ravo Weather Slik 61' 1.5 pl
Abound 80 WG 0.25 lb, Prnme Oil l v v .... ..........
Bravo Weather Stik 61- 1.5 pt
Abound 80 WG 0.25 Ib Prime Oil 1.0% vv ........ ........
Bravo Weather Stik 61- 1.5 pl
Abound 80 WG 0.375 lb- Prime Oil 1.0"' v,\ .. . ......
Bra\o Weathcr Slik 6F 1.5 pt
Abound 80 W G 0.375 Ib . .. ..........
13ravo Weather Stik l61 1.5 pl
Abound SO WG 0 ISS lb im il 1.0",, v ... ... ...
Bravo Weaclhr Stlk 61- 1.5 pt
Abound 8O WG 0.5 lbh Prime Oil I 0",. v.
icho 720 61 I 5 p...
Echo 720 61:F 1.5 pl
Echo 720 61: 75 pl n Ioicur 3 d"i -1., 4 1 o .
Echo 720 61- 1.5 pl
lolicur 3.61 4.0 11 oz Abound SO\VG 0.125 l.......
Echo 720 6F 1.5 pit
I'olicur 3.614.8 11 o/. Abound SOW\G (. 125 lb ....... ...........
Echo 720 61 1.5 pl
HG B32205 5.57 1 1.0 p .. ... ... ... ...........
ra o W ea her S ik 61 1.5 ... ...............................
IBra'vo'Moncul 5 281 2 13 pi .
13ravo Weather Stik 61- 1.5 pl
Bravo'Moncut 5 281 2 13 pt
Bravo Wealther Stik 6- 1.5 pl
Bravo'MoAncul 5.281- 2.0 pli
13ravo Weather Sik 61- 1.5 pli
B3ravoiMoncul 5.281: 2.13 pl .....
Bravo Weather Stik 61- 1.5 pl
11311923 91: 2.25 p .........................................
Bravo Wcallier Slik 61- I 5 pl
11311923 9F 2.0 pl ..... ......................................
Bravo Weather Stik 61- 1.5 pi
11311923 9 1 2 .25 p .. ........... .. ........ .....
B3ravo WeaC-lhc Slik 6I 1.5 pI
11 11924 91- 2.0 it .. .......
13ravo Wcalher Slik 61 1.5 pi
lolicur 3.6F -4.8 11 o/ Bra o Wealther Stik 61- .75 pl . .
Bra o Weather Silk 61 1.5 pl
Abound 80\VG 0.375 lb 11316311 I I" 1 '\ \...
Bravo Weallher Stik 61' 2.0 pl
Folicur 3 61:4.8 11 \I o/' Brav \ o Weather Slik 61: 75 pt IB1I 63 II l.)",, v .. ...


1-7
1.2,7
3-6
1.2,7
3-6
1.2.4.6,7
3.5
1.2.4.6.7
3,5
1.2,4.6.7
3, 5
1.2.7
3-6
1.2.4.6.7
3.5
1-7
1
2-7
I
2-7
1
2-7

2-7
1.7
2-6
1.6. 7
2-5
1.2.7
3-6
1. 2.7
3-6
1.3.5.7
2.4.6
1.2.6. 7
3- 5
1.2.6.7
3-5
1.2.7
3-6
1
2-7
1.2.4.6
3.5
1
2 -7


I.SD P, .05


1169
3147


2.7 73

4.6 128


2 4018

1 4069


4.0 123 3 4238

3.5 111 4 4586

4.3 152 2 3956

4.3 122 0 4078


3.8 108 2
5.0 167 12


4205
3538


3.8 126 4 4191

4.2 130 2 4637

3.6 120 2 4362

4.2 138 10 3824

5.4 185 7 3865

5.0 174 4 3942

5.3 179 3 3448

4.7 154 5 3716

4.8 155 4 4052

5.5 194 10 3383

5.0 178 4 3744

4.0 141 2 3692

3.7 107 6 3830

4.1 126 1 4484

2.5 63 9 3625


36 9 520


SSchedules were seven sprays (1 7) applied on 2-wk intervals beginning 34 days after planting.
2 Final leaf spot ratings were made on 19 Sep using the Florida 1-10 scale in which a I represents

healthy plants and a 10 represents plants killed by leaf spot diseases.
3 AUDRC represents the area under the leafspot disease rating curve.









Use of Disease Forecasting Models For Leaf Spot and Stem Rot Managemient in
Peanut The peanut cultivar Andru 93 was planted in Dothan fine sandy loam soil (pH 6.1) at the
North Florida Research and Education Center, Quincy, on 17 May 1996. Plots were four rows, 20
ft long, planted on 3 ft centers, with 4 seed per row ft. Treatments were applied to the center two
rows of each plot only and outer rows were used as spreaders. Plots were arranged in a randomized
complete block design with fungicide treatments as the variable. Plots were fertilized with 500 lb/A
of 3-9-18 prior to planting and 1000 Ib/A of gypsum was applied on 23 Jul to supply additional
calcium in the pegging zone. The insecticide Thimet 15G (6 lb/A) was applied at planting for thrips
control and Asana (3 oz/A) was applied on I Aug for control of leaf hoppers. Weeds were controlled
at planting using 2 pt/A of Prowl plus 1 pt/A of Dual, followed by 11 oz/A of Gramoxone plus 1 pt/A
of Basagran on 28 days after emergence. Rainfall was adequate for crop growth and disease
development with 1.4, 2.5, 6.2, 6.5, and 7 6 in. in May, Jun, Jul, Aug, and Sep, respectively.
Fungicides were applied to the plots using a CO,-powered backpack sprayer equipped with a 2-row
boom with three 8001 flat fan nozzles per row at 2.5 mph and 40 psi. Fungicide treatments were
applied according to the extension recommended schedule of seven applications or according to an
Envirocaster model or the AUPNUTS model. The Envirocaster models used included the Late Leaf
Spot model (NADV; spray at 10 ECI with 10 days protection) full season or the NADV for the first
50 days after planting followed by the White Mold model for days 50-100 (MWMA; spray at 7 ECI
10 days protection). The AUPNUTS model was used full season but with a fungicide change from
chlorothalonil to Folicur during the 50-100 day period. Plots were inverted on 23 Sep, 129 days after
planting and picked on 26 Sep. Leaf spot assessments were made periodically during the season
using the Florida 1-10 scale in which a one represents healthy plants and a 10 represents plants
completely defoliated by leaf spot diseases. Stem rot was assessed as hits per 40 row ft at inversion
and converted to the percentage of row ft with one or more disease loci.

The predominant leaf spot disease near the end of the season was early leaf spot. The
percentage limb rot was assessed at inversion but numbers were too low to be of consequence. The
lowest leaf spot ratings were achieved when the systemic fungicide Folicur was used as a block
treatment or in a tank mix with other fungicides. The incidence of stem rot in the plot area was
relatively low and Folicur, and Moncut typically did well in minimizing this disease. The tospovirus,
TSWV, was present in significant incidence but symptom development occurred too late in the season
to be a yield determinant. Yields were moderate, ranging from 1679 lb/A for the check to 4286 Ib/A
for one treatment which included a scheduled 6-spray mix of Folicur at 4.8 oz/A and tank-mixed with
Bayer CL at 0.75 pt/A. Six applications of fungicide were made according to the Envirocaster and
models on 19 Jun, 8 Jul, 29 Jul, 13 Aug, 28 Aug, and 9 Sep. Five applications of fungicide were
made according to the AUPNUTS model on 19 Jun, 8 Jul, 29 Jul, 13 Aug, and 28 Aug. Seven
applications of fungicide were made according to the extension recommended schedule on 19 Jun,
3 Jul, 17 Jul, 31 Jul, 13 Aug, 28 Aug, and 9 Sep.












Table 4 Comparison of disease forecasting models used to determine when fungicides were required


for leaf spot and stem not management in 1996.


lTreatmen Raie/A and anlnlic:aiion riuLcr
U treated C heck . ..................
Bravo W weather Stik 6F 1.5 pt ...............
Echo 720 6 F 1.5 pt .....................
Bravo W weather Stik 6F 1.5 pt .......... ...
Echo 720 6 F 1.5 pt .....................
Bravo Weather Stik 6F 1.5 pt
Folicur 3.6 F 7.2 fl oz + Induce .06% v/v .......
Echo 6F 1.5 pt
Folicur 3.6 F 7.2 fl oz + Induce .06% v/v ...
Bayer CL 6F .75 pt + Folicur 3.6 F 4.8 tl oz ....
Bravo Weather Stik 6F 1.5 pt
Bravo/M oncut 5.28F 2.125 pt ...............
Bravo Wcathcr Stik 6' 1.5 pi
11311923 9F 2.25 rt ... ..........
Lcho 720 6F 1.5 pl
Ia\'cr CI. 6F 75 pl l:licur 3 6 I -4.8 11 o .
Bravo Wc;lhcr Slik 61: I 5 pi
Folicur 3.6 F 7.2 11 o/. Induce .06", % 1 .
1.SD P- .05


Spray Percent
schedule' Siemrol
26
1 -7 19
1 -7 16
NADV 10
NADV 9


NADV
NWMA
NADV
NWMA
NADV
NADV
NWMA
NADV
NWMA


Final
LealspotP
9.5
5.1 1
4.6
4.3
5.2


3 3.5


8 5.6


AUI)RC3
318
155
144
132
159


Pod Yield
Ib/A
1679
3186
3668
3339
3106


105 4013

104 3693
80 4004

178 3274


11 4.8 159 3755


NADV


3.6 98 4286


AUJNULTS 5 3.0 89 3855
10 1.0 41 517


SSchedules represent either an extension schedule of seven sprays (1 -


7) beginning 19 Jun and


continuing at 2 wk intervals, or a disease forecasting model (late leaf spot NADV) as forecast by
an Envirocaster (Neogen Corp. East Lansing, MI), or the late leaf spot model with a stem rot model
(NWMA) during 50 100 days after planting, or the AUPNUTS model.
2 Final leaf spot ratings were made using the Florida I 10 scale in which 1 represents healthy plants
and a 10 represents plants killed by leaf spot diseases.
AUDRC represents the area under the disease response curve.


I-




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