Grape Disease Risks: 5/15 – 5/22/2024

At Winchester, our Chardonnay vines are in the trace bloom stage. This is the earliest bloom since I joined VT in 2009.

Here’s a snapshot from the last week, showing the number of days with the risk of each disease: Ph = Phomopsis, PW = Powdery mildew, BR = Black rot, and DM = Downy mildew. N/A means there is no data or some issues with the NEWA. Since last week, we have been using a different downy mildew model due to inconsistency with the NEWA model. This model uses the past five days of weather to estimate spore production and the next seven-day forecast to estimate the infection risk.

Due to relatively low relative humidity during the nighttime, risks of downy mildew have been low. However, we expect rains in the next several days, and vines are probably at or close to bloom; thus, extra caution against downy mildew (and black rot while you are at it) may benefit you. Please see my presentation slides from the last meeting for more detailed recommendations.

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