In the past few days, we had about 2 inches of rain at Winchester, but I heard that there were up to 5 inches rains observed in some places. Since the afternoon of May 25th, we have been having either rain or high relative humidity conditions continuously (RH is still above 90% as of 10:30pm 5/28/09, thus potentially, we have > 60h of wetness). Average temperature during this period was 67F in 25th, and 60F in 26th and 27th. These conditions are good enough for Phomopsis infection, powdery mildew ascospore discharge, black rot infection, and downy mildew spore production and infection.

If your vines are very close to bloom or blooming, it is the critical timing for many of these disease development. As I mentioned earlier, there are some fungicides you can use after infection events. For powdery mildew, you can use any of fungicides you typically use (even sulfur) because the fungus grow on grape tissue superficially. For black rot, Rally (mycrobutanil) has a good curative effect. For downy mildew, Ridomil products and Phosphorus acid products has a good curative effect. No curative fungicide against Phomopsis. You can apply these products up to 6 days after infection in most of the cases, but to be safe side, it is probably wise to apply 2-4 days after infection. (because downy mildew and powdery mildew may take only 7 days after infection to produce spores under optimal conditions)

As I mentioned yesterday, disease developement depends on many factors. I’m showing these infection information to aid your decision making process, but ultimately, you are the one who know more about your vineyards than anybody else. For example, you may have sprayed last week, your vineyard may have received only 1 inch of rain, and the vines may not be ready for bloom. Then you do not need to panic. In addition, please think about history of your vineyards, varieties, etc. Also, don’t forget about cost of application (to your wallet and to the environment) too.