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Ask Your PCA: How should farmers combat walnut blight?

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Issue Date: February 10, 2021
Justin Nay PCA, Integral Ag Services, Durham
Justin Nay

Walnuts are in a tough economic spot and growers are looking for ways to reduce overhead. When it comes to blight management, growers could be looking for the cheapest rates and materials.

North State growers typically have more problems with walnut blight because of weather—specifically rain. All walnuts are susceptible to blight, but there is more inoculum in the Sacramento Valley versus the San Joaquin Valley.

The early varieties planted in the north tend to have more blight and rain events. Historically, Tulare, Vina and Howard varieties are the most susceptible to blight, but there have also been problems in the new Solano variety.

In a tight economic year, prioritizing blocks at highest risk for blight could be the best solution.

A copper/Manzate application has been used for blight prevention, but some blocks have become resistant to copper. Kasugamycin was released about three years ago, but few growers have used it. For blocks that have resistance, Kasugamycin would be a better choice.

If growers wait until a rain event is approaching, it may be difficult to get through all blocks to make applications in a timely fashion. Saturated orchard floors can also make it difficult to get equipment in, leaving aerial applications as the only option.

Aerial applications have been used more and more because of labor shortages. In 2020, the cost and availability of labor made aerial applications much more competitive. Growers may also look to aerial applications and then wait to see if a rain event actually happens, rather than spray preventively.

Aerial applications do have drawbacks. They aren't as precise as ground applications except with old, tall walnut trees or dense plantings where ground applications can't effectively reach the tops of the trees. A ground application could be done in unfavorable weather, whereas airplanes and helicopters could be grounded under certain weather conditions.

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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