Grape Disease Risks: 5/22 – 5/29/2024

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. This year, 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 mean temperature and humidity during the nighttime, risks of downy mildew have been low. However, most vines are around bloom time; 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.

One of the common insect pests you may see around bloom is grape berry moth, which appears as webbing within the cluster (please see the upper part of the cluster on the left). This insect has several generations per year and can cause damage by feeding inside berries. For more information on management, please refer to our Pest Management Guide.

The NEWA, which I use for disease risk assessment also has a function to predict grape berry moth, which is based on growing degree days. For more information, please refer to their website. Our labs are paying annual fees, so, please take advantage of this great tool.

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