Typically, the ideal time to begin treatment is when 30-40 40 percent of the shoot-flower buds reach the prayer stage. This is when the terminal leaves of pistillate flower buds begin to unfold, similar in shape to hands in a prayer position.

Tehama County’s relatively few early walnut varieties, including Ashley and some Serr, reached this point in mid-March which was earlier than usual, Buchner says.

The later Chandler and Howard varieties, the bulk of Tehama County’s walnut acreage, followed close behind. Normally, these varieties don’t reach the 30-40 percent prayer stage until the first week of April.

“Fortunately, rain events were accurately predicted and growers were able to apply protective sprays prior to the rainfall,” Buchner explains.

He recommends making a second spray 7-10 days after the first application to treat the pistillate flowers not open enough for the first spray.

“If you achieved good coverage with the first and second applications, then watch the weather forecasts and be prepared to make additional treatments as needed, particularly if Xaj populations are high,” according to Buchner.

Given the right temperature and moisture conditions, walnut blight can remain a threat until nuts reach full size, the husk matures, and the rain is over.

“Late infections don’t typically destroy the kernel,” he says. “But, they can produce lesions on the husk which can attract secondary pests, including the Navel orangeworm.”

Aside from walnut blight and the other walnut disease and insect crop risks, Buchner says a major concern for Tehama County growers this year is low walnut prices.

“In order to compete in the down market, growers will have to produce good yields and high-quality kernels this year,” he says. 

“This will require proper irrigation management. Applying two much water can suffocate the tree roots while under-watering can stress the trees. Either way, walnut quality can suffer.”