By the official start of summer last month, the walnut orchards of PCA/CCA Rod Walker’s growers were looking much better than even a few weeks earlier.

His business, Professional Crop Consulting/Applied Bio Control, Waterford, Calif., works with walnut growers in Merced, Stanislaus, San Joaquin and Sacramento counties.

The turnabout followed the persistent and unusually cool, wet spring, which included about 1.25 inches of rain at the beginning of June.

“By the third week of June, temperatures had warmed up and the trees were looking good,” he says. “And, because the soils were finally drying a little, the trees were losing their yellow look and starting to get a new flush of growth”.

The cool spring weather helped depress walnut aphid numbers. Normally, he sees quite a few of the pests by the start of summer. He saw a few in the third week of June, including some parasitized by the small wasp, aphitus.

“It’s interesting that we had little or no walnut aphid activity up to that point,” Walker says. “Maybe they are just late in developing and will be coming later. If that happens, though, the population of natural predators, including aphitus and green lacewing, may be high enough by then to take out the aphids.”

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