A rainy weekend brought our area two estimated wetness periods (19h with 73F, and 20h with 64F), plus additional 30h+ hours of high humid condition (RH>90%) (note: some of you might have ended up with 50+ hours of wetness period.  We only had about 3 hours where RH dropped below 90% on Saturday).  The wetness periods were infection events for Phomopsis, black rot, downy mildew, and Botrytis.  (note 2: your vines should be over with a critical period for berry infection for black rot and downy mildew.)

In addition, the extensive humid condition probably favored downy mildew spore production.  As you know, severe downy mildew infection can cause defoliation.  If you are debating whether you should apply a downy mildew material or not, you can scout for downy mildew symptoms.  At this time of the year, it tends to show up on younger (= upper part of the canopy) leaves because these are more susceptible than older leaves.

At this point, people often use Phosphonates (Phosphorous acid, Prophyt, etc) material which can provide both protective and kick-back activities.  It is often applied with captan to increase the protective activity.  The alternative is Ridomil with Copper, but please note that it has 42-day PHI.  If you are looking for a protective material for downy mildew, you can use Revus (Revus or Revus Top, 14-day PHI), Ziram (21-day PHI), Captan (0-day PHI), Ranman (30-day PHI), Pristine (14-day PHI) etc.  (Note 3: Pristine may or may not provide you a good control against downy mildew since QoI resistance is commonly found in VA).