Ask Your PCA: How do growers best deal with walnut blight?

Issue Date: January 29, 2020
Justin Nay PCA with Integral Ag Services in Durham
Justin Nay

Walnut blight is of concern particularly for northern Sacramento Valley growers and with the older varieties like Ashley, Hartley, Tehama and Serr. These are varieties that mostly bloom early and tend to see more rain events, which equals more problems with walnut blight.

Chandlers, on the other hand, bloom late and have fewer problems with walnut blight. There are some new plantings of the Solano variety that appear to have problems with blight. It is still unknown about the new Durham variety.

Last year, growers had problems with blight because of rain well into May. Even the Chandlers had some problems with the disease, but at lower levels than other varieties.

In the north valley, it was a challenge to get on the ground and spray last year. If growers missed a window to make an application, it was weeks before the ground was dry enough to get back in again.

Aerial applications are an option, and they have become more competitive because of the cost and availability of labor.

Walnut blight has been controlled with Manzate, Nithane, Manzacob along with coppers—fixed copper and other formulations that have less metallic copper. A new product, Kasumin, is available.

Timing of spray applications are dependent on several things:

  • Stage the catkins are at.
  • If the ranch has a history of walnut blight.
  • How susceptible the trees are to walnut blight.

Treatments can be applied in advance of a rain event, but if the weather is warm and the trees are pushing, there will be new growth that isn't protected. Applications made a day in advance of a rainstorm will dry in just a few hours and provide sufficient protection. If an application can't be made before the rain, spraying a day or two after can still be effective and limit the spread of the disease.

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




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