Virginia Grape Disease Updates

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Showing posts from August, 2013

Disease risks from Aug 28-29th

A rain event followed by high relative humidity (+28 hours of wetness in high 60F) created disease risk event for downy mildew and Botrytis on 8/28-29.

Disease risk from yesterday

A wetness event recorded yesterday was infection event for Botrytis and Downy mildew. Refer to yesterday's post on spray choices. Please make sure to alternate mode of actions to reduce the risk of fungicide resistance development.

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.

Disease risks 8/9-8/13

Botrytis risk has been high from 8/9 to 8/13 due to frequent rain event. This also means that downy mildew risk is high too. (I am at a conference, so, I cannot provide detailed data. I will update it once I am back this weekend.)

Disease risks from 8/6 and 8/7

On 8/6 a wetness event (~10 h in lower 70F) was recorded at Winchester, and there was another event today (~16 h in lower 70F)... Both are risk event for Botytis and downy mildew.

Disease risks 8/3-8/4

There was ~27h wetness event recorded between 8/3-8/4 with temperature varying from upper 60F to lower 70F. It was an infection event for Botrytis and downy mildew.

Disease risks from 7/31-8/1

Between 7/31-8/1, there was several wetness hours recorded, and one of them was 16h with an average temperature of low 70F. It was a disease risk event for downy mildew and Botrytis.