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Evaluation of fungicides for control of powdery mildew (Uncinula necator) of grapes, 2002.

B. Hed and J. W. Travis
Lake Erie Regional Grape Research and Extension Center, North East, PA 16428
Penn State Fruit Research and Extension Center, 290 University Drive Biglerville PA 17307-1330

This trial was conducted with mature Vitis interspecific hybrid 'Chancellor' at the Lake Erie Regional Grape Research and Extension Center, North East, PA, where vines were trained to a single curtain, (no tie) system. Treatments were applied to 4-vine plots in a randomized complete block design with 4 replications. Fungicides were applied with a Friend covered-boom plot sprayer at 200 psi, and 100 gal/A. Rainfall for Apr, May, Jun, Jul, Aug, and Sep was 7.42, 8.13, 2.33, 2.61, 3.16, and 6.58 in, respectively. Powdery mildew disease incidence and severity were determined 13 Sep from 25 leaves and clusters per plot.

Results

Powdery mildew disease pressure was high. Wet weather in May and early Jun brought about the development of sporulating powdery mildew lesions relatively early in the season. Lesions were first observed on leaves and cluster rachises on 9 Jun, nine days prior to bloom. The bloom and early fruit set period were dry, and there were no primary infection periods from immediate pre-bloom through 2 weeks post-bloom, but conidial inoculum on rachises and leaves placed susceptible flowers and developing berries at risk of infection. A disease assessment on 9 Jul (data not shown) revealed that all programs were providing significant control of disease incidence on leaves early in the season, but by mid Sep, incidence on leaves was nearly 100 % in all treatments. Only treatments containing BAS 516 significantly reduced the severity of leaf disease and the incidence of clusters with berry infections. All treatments controlled the severity of berry infections. Control of powdery mildew by demethylation inhibiting and strobilurin fungicides was worse in this vineyard than in previous seasons and these results suggest that strains of U. necator have developed a reduced sensitivity to these fungicides in this vineyard. There was no phytotoxicity associated with any of the treatments.

Treatment and rate/A	Timingz	% Area Leaves Infectedy	% Clusters with Berry Infectionx		% Area Berries Infectedy
BAS 516 UD F 0.658 lb/A	1-7	18.37 aw	69.0 a		1.62 a
BAS 516 UD F 0.395 lb/A	1-7	20.33 a	66.0 a		1.55 a
Rubigan E.C.2 oz/A
BAS 516 UD F 0.395 lb/A
Rubigan E.C.6 oz/A	6	29.03 a	84.0 ab		1.99 a
Rubigan E.C.2 oz/A	3
Sovran 50WG 4oz/A	4, 5, 7
Rubigan E.C.6 oz/A	6	70.98 b	100.0 c		4.03 a
Rubigan E.C.2 oz/A	3
Flint 50 WGD 2oz/A	4, 5, 7
Rubigan E.C.6 oz/A	6	74.68 b	100.0 c		4.45 a
Serenade WP 6 lb/A	3, 6, 7
Rubigan E.C.5 oz/A	4
Sovran 50WG 4oz/A	5	76.07 b	98.0 bc		3.44 a
Untreated Check		87.69 b	100.0 c		19.99 b