Absent a regular spray schedule, powdery mildew will show up on susceptible varieties like clockwork. Furthermore, varieties that are not normally susceptible will host powdery when it gets into the vineyard on a susceptible variety. Humid conditions, a canopy that does not get enough air drainage and a fruit zone that is too tight and too shaded combine to invite infestation.
We have a good arsenal of systemics for control of powdery and reasonably effective organic protecion (see Organic Grape Growing section). Material should be alternated to prevent powdery spores from developing a resistance. Alternating with sulfur and one systemic of your choosing should also do the trick.
If powdery slips through your control net, hit it with sulfur (check for varietal sensitivity to sulfur and do not spray in full sunlight). Use a surfactant. After one or two sulfur applications, go back to the systemics.
Sometimes powdery shows up just before harvest. The pre-harvest limitations on the spray materials may have kicked in. Sulfur may be used right up to the day of harvest, but re-entry into the vineyard is restricted to 24 hours after application. An alternative is to take advantage of the slow movement of powdery and get the fruit out before you spray.
By the way, we once removed a lilac bush near our vineyard because it was serving as a great host for powdery. Recently, we learned that the mildew on lilacs does not attack grapes. Alas, when the lilacs last round the vineyard bloomed, we were there with our saw.
|September, '99: Promising Cornell Research|
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