A quick reminder about downy mildew

Just a quick note that recent rain events were risk events for downy mildew based on the NEWA DMCast model. It seems that northern VA received more and longer rain events. In addition, we may see more rain toward the end of next week.

DMCast results at Crozet station

(green cells indicate downy mildew infection events)

DMCast results from Winchester station

Since we have been experiencing a very dry season, I was not really thinking about downy mildew. However, during recent vineyard visits, I have noticed downy mildew on leaves, and sure enough, I saw some downy mildew lesions on leaves in one of my research blocks too.

Early downy mildew lesions may not be very obvious.

If you are due to spray soon, grow downy mildew susceptible cultivars (e.g., Chardonnay, Vidal, etc.), and/or have seen a considerable amount (or duration) of rain recently, it may be a good idea to include a Phos acid material (e.g., Prophyt, Phostrol, Agri-Fos, etc.) in the tank mix as insurance. Please note that if you use a copper material, a combination of copper and phos acid can cause phytotoxicity. Since many of our vines are in the critical period to protect clusters from downy mildew, powdery mildew, and black rot, the use of a Ridmil product may also be a good idea.

For more details on "at bloom" fungicide applications, please refer to my previous post.

Comments

Downy mildew gallery

At Winchester, we had light rain events during the night of 6/12/09, but it was short events and the relative humidity was low (80% or so), thus it probably did not promote any infections. However, we are experiencing continuing favorable nights for downy mildew sporulation (average T>55F, high RH (80-100%)) for 10 days now. Yesterday, we conducted a formal disease assessment, and observed first incidence of powdery mildew for this season. We had plenty of infection events in last two months, so it was not surprising. At this point, it is a trace level of infection on untreated vines. Downy mildew was the major disease so far. We had up to 40% incidence on untreated vines. Next runner-up was black rot. It varies vine to vine, but some of vine had 10-15% incidence. Phomopsis was omnipresent as I expected from early May rain falls, but severity was low overall. We will examine diseases again in the near future, and I will update as the season goes. Here is downy mildew ga...

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Recent downy mildew risk events

It seems that several rain events have happened over the course of the past two weeks or so. Here is a summary of recent downy mildew risk events, based on the NEWA stations and DMCast. Bristol, VA Fifteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Floyd, VA Eleven days with potential DM infection event(s) since Sept 1. The last event happened last Friday. Charles City, VA Twelve days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Central VA Since there was a wide variation among stations, I am listing several around Central VA. Tyro, VA Nine days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Red Hill and Crozet, VA Only one day with potential DM infection event(s) since Sept 1. Olympic Lake Thirteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Washington, VA Eight days with potential DM infection e...

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