LERGREC
| Plant Pathology | Fungicide Efficacy
Trials 2001
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Evaluation of Fungicides for Control of Botrytis Bunch Rot of Vitis interspecific hybrid 'Vignoles' Grapes, 2001.
J.
W. Travis and B. Hed
Penn State Fruit Research and Extension Center, 290 University Drive Biglerville
PA 17307-1330
Lake Erie Regional Grape Research and Extension Center, North East, PA
16428
This trial was designed to: 1) compare the efficacy of 2 applications of Vangard at different stages of cluster development, and a full season program (4 applications of a botryticide) and 2) evaluate Switch for efficacy on Botrytis bunch rot. The trial was conducted with eleven year old vines trained to a single curtain (no tie) system at the Lake Erie Regional Grape Research and Extension Center, North East, PA. Treatments were applied to 3-vine plots in a randomized complete block design with 4 replications. Fungicides for Botrytis bunch rot were applied with a Friend covered-boom plot sprayer at 200 psi and 100 gal/A. Other diseases were controlled with applications of Dithane 75DF (4 lb/A) and Nova 40W (5 oz/A) on 31 May, Penncozeb 75DF (4 lb/A) and Elite 45DF (4 oz/A) on 13 Jun and 11 Jul, Penncozeb 75DF (4 lb/A) and Nova 40W (5 oz/A) on 26 Jun, and Nova 40W (5 oz/A) on 23 Jul, using a Kinkelder air blast sprayer. Rainfall for May, Jun, Jul, Aug, and Sep was 5.88, 4.13, 4.46, 6.88, and 4.09 in., respectively. Botrytis bunch rot incidence was determined on 28 Aug, and incidence and severity on 23 Sep, from 50 randomly selected clusters in the center of each plot.
Results
Botrytis bunch rot infections first appeared the week of 20 Aug (sugar levels were about 12 Brix) and were primarily associated with damaged berries as a result of berry expansion in tight clusters (split or torn berries, berries detached from their pedicels). No chemical treatment programs provided significant control of Botrytis bunch rot. The occurrence of damaged berries across all treatments, likely obscured differences in the performance of the treatments. Monitoring studies in the same Vignoles vineyard block, revealed that overcrowding in tight clusters is a major factor in the predisposition of Vignoles clusters to bunch rot, and that dramatic reductions in disease are possible, with or without fungicides, if berry overcrowding can be reduced.
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Botrytis
Bunch Rot
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%
Clusters Infected
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%
Area Clusters Infected3
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| Treatment and rate/A |
Timing1
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28
Aug2
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23
Sep
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23
Sep
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| Rovral
50WP 1.5 lb/A + .06% Latron B-1956 |
1,
2
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| Vangard 75WG 10 oz/A |
3,
4
|
3.0
ab4
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29.55
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6.845
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| Vangard 75WG 10 oz/A |
1,
2
|
2.5
ab
|
37.5
|
7.64
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| Vangard 75WG 5 oz/A |
2, 3
|
1.0
ab
|
37.0
|
6.91
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| Vangard 75WG 10 oz/A |
2,
3
|
0.0
a
|
36.5
|
5.89
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| Vangard 75WG 10 oz/A |
2,
4
|
3.0
ab
|
44.0
|
8.09
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| Vangard 75WG 10 oz/A |
3,
4
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6.0
b
|
46.5
|
8.88
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| Switch 62.5WG 10 oz/A |
2,
4
|
3.5
ab
|
38.0
|
7.46
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| Switch 62.5WG 14 oz/A |
2,
4
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2.5
ab
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33.5
|
5.76
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| Vangard 75WG 10 oz/A* |
3*,
4
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4.0
ab
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37.0
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7.16
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| Untreated Check |
3.5
ab
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45.0
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9.64
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1 Application dates: 1 = 25 Jun (full bloom); 2 = 9 Jul (pre-close); 3 = 14 Aug (6.5o Brix); 3* = 21 Aug (about 12.0 Brix); 4 = 9/11 (about 20 Brix).
2 Actual data are shown. Data were transformed by square root transformation before statistical analysis.
3 Severity was rated using the Barratt-Horsfall scale and was converted to % area infected using Elanco conversion tables.
4 Means followed by the same letters within columns are not significantly different according to Tukey-Kramer (P < 0.05).
5 No significant differences according to Tukey-Kramer (P < .05).
6 Delayed 1st spray until 1st disease (after 5 Brix). Subsequent sprays based on disease pressure.
