Grape Disease Risks: 5/8 – 5/15/2024

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.

Despite the rains, downy mildew risks were low because the nighttime temperatures were also low and did not meet the requirements for spore production. Overall, black rot risks are low, too, probably due to the same reason (i.e., low temperatures). On the other hand, powdery mildew risks have increased. If you have cultivars that are susceptible to powdery mildew, you may want to tighten up your spray program. Please see my presentation slides from the last meeting for more detailed recommendations.

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