Disease risks 8/14, 17, and 20

Continuous rain and high relative humidity caused Botrytis and downy mildew infection risk events on the 14th, 17th, and 20th.

At this point of the season, a phosphite (aka phosphonate or phosphorous acid) material would be the best choice for downy mildew. You may want to mix it will captan to have added efficacy. (Note: captan has 0-day PHI, but some winemaker prefer not having captan close (~3 weeks) to the harvest.) The other potential mixing partner would be Ranman (note PHI = 30 days), Forum (PHI=28 days), or Revus (PHI=14 days). Ranman should have some kick-back activity, and both Forum and Revus have a protective activity.

As for Botrytis, we only have protective action materials, thus, please make sure to have a good coverage on your clusters. Moreover, please make sure to rotate mode of action since this pathogen is known to develop resistance to fungicide rapidly.

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

Season's Greetings!

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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 event

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