Thursday, April 28, 2011

Disease risks from today's rain

As with other regions in VA, Winchester area observed a series of thunderstorms this morning.  It started from 2:40AM and lasted until 7:30AM or so.  The RH was high (>90%) until 8:40AM, thus, it accounted for 6 hours of estimated wetness with 68F as the average temperature.  It was a light infection risk for Phomopsis, and a borderline case for black rot.  Also, since the average temperature was high, it was a risk event for downy mildew as well.

The other concern is the wash-off of the fungicide(s) on the leaf surface  We had about 1 inch of rain with this event.  A typical rule of thumb for fungicide application timing is  "2 weeks or 1 inch of rain whichever comes first", thus, this and a series of rains we had since last Sunday might washed materials off from your vines.  However, please keep in your mind that the risk of disease development also depends on a history of disease(s) in your vineyard, and also, you need to take the weather forecast into account for your planning.

The chance of precipitations in next few days are low (less than 30%) in our area.

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