Recent rain events and downy mildew spray

Central and northern VA received much-needed rains in the past two days. Looks like the chance of thunderstorm is high in today and tomorrow too. Several people asked me whether they need to jump on their tractor now and spray for downy mildew or not.

Here are snapshots of downy mildew risk events in three locations during the past two weeks.

Southwestern VA, Floyd: none
Central VA, Afton: 7/11, 7/22, and 7/23
Northern VA, Winchester, 7/11 (a very short one) and 7/22

Since we have been experiencing a very dry season, I do not think we need to react to every rain event, especially if your previous spray was less than 7-10 days ago. If you are due to spray soon anyway, it may be a good idea to have a Phos acid material (e.g., Prophyt, Phostrol, Agri-Fos, etc.) in the tank-mix as insurance.

For example, my previous spray (a fixed copper material) was on the 11th and my plan is to spray my vines this Saturday (the 25th) with a Phos acid, sulfur, and another PM material (Vivando, Quintec, or Torino). Although my spray was made 12 days ago, I am not too concerned about downy mildew because we scouted vineyard recently. We had a downy mildew trial this year, and out of nearly 2,000 leaves I assessed, there were only two leaves with symptoms. Not good for us, but good for everybody else!

Speaking of scouting, I am developing a new scouting form. If you are interested in, please check the instruction and Excel sheets (VT version (preferred) and a modified-MSU version for those of you who have been using this form). If you use this form, please give me a feedback so that I can improve.

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