July 8, 2016
Grape disease management remains a concern, but as vine and berry susceptibility to black rot and phomopsis wanes, focus should shift toward powdery and downy mildews and botrytis. Revus Top (fungicide resistance class (FRAC) 3 & 40) is effective against the mildews but not botrytis (which may be less of a concern on less-susceptible cold-climate cultivars in this relatively dry year), but there are reports of some foliar damage from its use on Prairie Star, Adelmiina, and Louise Swenson from one Vermont grower. Strobilurins (FRAC 11) are also effective against downy and powdery mildews, and have some efficacy against botrytis. Pristine (FRAC 7,11) , Vangard (FRAC 9), Inspire Super (FRAC 3,9) , Rovral (FRAC 2) , and Scala (FRAC 2) are some materials effective against botrytis. Remember that fungicide classes must be rotated to avoid resistance development by disease-causing organisms.
Organic growers are limited to sulfur, coppers, potassium and biological materials. Sulfur is effective against powdery mildew but may cause phytoxicity on some cultivars; Louise Swenson is one that is particularly sensitive. JMS stylet oil and potassium bicarbonate are also effective against powdery mildews when applied soon after infection occurs, they have limited protective activity. Copper is effective against downy mildews but should be limited to a few application per year to reduce buildup in the soil and potential for phytotoxicity. It is also somewhat effective against botrytis when applied early in its infective season (like, now). Biological materials are more a question as to efficacy; there are a lot out there, but few have been shown to be really good against many diseases, compared to conventional materials. All of the organic and biological materials work best in low-inoculum situations (and drier seasons, like this one) so meticulous sanitation through removal of infected leaves and other tissues is critical to improve their effectiveness. Regalia has shown some effectiveness against powdery mildew but likely no more than sulfur or oil, and Double Nickel shown good effectiveness against both downy and powdery mildews under low pressure conditions.
Grape berry moth are flying and laying eggs now. A broad-spectrum insecticide like a carbamate or pyrethroid is effective against egg-laying adults; more precise control of hatching larvae may be had using Bt, Delegate, Intrepid applied to hatching eggs in the next week or so.
Canopies should be aggressively combed and clusters exposed to sunlight by removing lateral shoots and some leaves if necessary; the sooner this is done the better the effect and the more resistant grapes will become to sunburn.