LERGREC | Plant Pathology | Fungicide Efficacy Trials 2000 You are here

Evaluation of fungicides for control of downy mildew and powdery mildew of 'Chancellor' grape, 2000

The objective of this trial was to examine the efficacy of three strobilurin fungicides, Kresoxim methyl (Sovran), Trifloxystrobin (Flint), and BAS 500, for the control of powdery and downy mildew of grape (cv. 'Chancellor'). Each of these fungicides was applied alone (solo) in a season long program, and as a tank mix with Mancozeb (Penncozeb) and Ziram. These treatments were compared to standard treatment programs of Penncozeb (mancozeb)/Nova (myclobutanil)/Ziram, and an unsprayed check.

This trial was conducted in a ten-year-old vineyard at the Lake Erie Regional Grape Research and Extension Center, North East, PA. Vines were trained to a single curtain, high wire cordon system, and 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, applying 100 gal/A. Rainfall for May, Jun, Jul, Aug, and Sep was 5.26, 5.04, 5.63, 2.12, and 5.69 in. respectively. Rainfall for May, Jun, Jul, Aug, and Sep was 5.26, 5.04, 5.63, 2.12, and 5.69 in, respectively. Bud burst occurred on 4 May and full bloom on 16 Jun. Disease incidence on 25 Jul was determined from 50 randomly selected leaves and clusters per plot. Incidence and severity were determined on 24 Aug and 20 Sep from 25 randomly selected leaves and clusters per plot. Severity was rated using the Barratt-Horsfall scale and was converted to % area infected using Elanco conversion tables.

Results

Powdery Mildew: Disease pressure was relatively high, due to adequate rainfall that resulted in frequent primary infection periods. A pre-bloom and two post-bloom applications of Sovran, Flint (applied at the rate for downy mildew suppression, which is twice the rate for powdery mildew control), and BAS 500, were as effective as the season long programs of these materials respectively, suggesting that sprays 1 (3.6 inch shoots) and 2 (8.9 inch shoots) had a relatively small effect on powdery mildew development in this season. The Flint and BAS 500 treatments provided significant control of leaf, rachis, and berry infections. Sovran's performance was somewhat weaker. The Sovran treatments did not significantly control rachis infections and fell just inside of (season long (solo) treatment) or outside of (pre-bloom through 2nd post-bloom) significant leaf infection control. However, both Sovran treatments provided significant control of berry infections. Two pre-bloom plus two post-bloom applications of Nova (standard), failed to significantly reduce leaf, rachis, or berry infection over that of the untreated check, but did provide a level of control that was statistically equivalent to all other fungicide treatments with regard to berry infection and all treatments except the Flint and BAS500 solo programs with regard to leaf infection. Extending the standard treatment program by one additional application of Nova (VITIS treatment), extended protection beyond 3 weeks post-bloom to 4-5 weeks post-bloom with a resulting 5 % increase in the level of control on berries. This supports research by other investigators that berries of susceptible French hybrid varieties (like 'Chancellor') may be susceptible to powdery mildew until 4-5 weeks post bloom.

Downy Mildew: Disease pressure built up slowly, remaining low throughout most of the block. By August, an assessment of disease in all unsprayed buffer plots within the experimental block made it apparent that disease pressure was unevenly distributed and that some plots were more challenged by downy mildew than others. As a result, variability between plots of the same treatment (particularly with respect to downy mildew on clusters) was high. To further confound matters, most of the plots of the unsprayed check, both treatments containing Flint, and the BAS 500 solo treatment, were in areas of relatively low disease pressure. On the other hand, most of the plots of the treatments containing Sovran, particularly the solo treatment, were in areas of relatively high disease pressure, and were likely challenged the most. In support of this, more severe disease developed in the Sovran solo treatment than the unsprayed check.. Better control was observed when Sovran or Flint were combined with reduced rates of Penncozeb and Ziram than when these two strobilurins were applied alone season long. BAS 500 alone and combined with Penncozeb and Ziram provided complete control on clusters.

20 Sept.		Downy Mildew					Powdery Mildew
		Leaves		Clusters			Leaves	Clusters
								Berries	Rachis
		%	%Area	%	%Area		%Area	%Area	%Area
Treatment and rate/A	Timing1	Infected	Infected	Infected	Infected		Infected	Infected	Infected
Sovran 50WG 5 oz	1-5	76.0 cd2	1.85 cd2	61.03	11.413		72.61ab2	1.43 a2	82.41 c2
Penncozeb 75 DF 4 lb	1, 2
Penncozeb 75 DF 3 lb + Sovran 50WG 5 oz	3, 4
Sovran 50WG 5 oz + Ziram 76 DF 3 lb	5	50.0 abc	1.17 abc	24.0	3.48		73.67 abc	1.19 a	77.96 c
Flint 50 WDG 4 oz	1-5	76.0 cd	1.92 cd	28.0	3.99		59.80 a	0.30 a	53.43 b
Penncozeb 75 DF 4 l b	1, 2
Penncozeb 75 DF 3 lb + Flint 50 WDG 4 oz	3, 4
Flint 50 WDG 4 oz + Ziram 76 DF 3 lb	5	33.0 ab	0.77 ab	6.0	0.14		65.67 ab	0.40 a	50.16 ab
Standard treatment A Penncozeb 75 DF 4 lb	1
Penncozeb 75 DF 4 lb + Nova 40 W 4 oz	2, 3
Nova 40 W 4 oz + Ziram 76 DF 4 lb	4, 5	51.0 abc	1.22 abc	32.0	4.81		81.89 bc	4.28 ab	95.21 c
Standard treatment B Penncozeb 75 DF 4 lb	1
Penncozeb 75 DF 4 lb + Nova 40 W 4 oz	2, 3
Nova 40 W 4 oz + Ziram 76 DF 4 lb	4-6 4	59.0 bcd	1.38 bc	33.0	3.71		81.96 bc	3.41 ab	95.79 c
BAS 500 20WG 12oz	1- 5	15.0 a	0.35 a	0.0	0.0		58.65 a	0.19 a	38.58 ab
Penncozeb 75 DF 4 lb	1, 2
Penncozeb 75 DF 3 lb + BAS 500 20WG 12oz	3, 4
BAS 500 20WG 12oz + Ziram 76 DF 3 lb	5	33.0 ab	0.77 ab	0.0	0.0		65.74 ab	0.19 a	29.58 a
Untreated Check		95.0 d	2.51 d	41.0	7.54		90.00 c	17.09 b	97.31 c

1 Dates for spray timings: 1 = 12 May; 2 = 26 May; 3 = 9 Jun; 4 = 20 Jun; 5 = 2 Jul; 6 = 13 Jul
2 Means followed by the same letters within columns are not significantly different according to Tukey-Kramer (P < 0.05).
3 No significant differences according to Tukey-Kramer (P < .05).
4 Sixth application on 13 Jul timed by VITIS expert system.