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 late spring rains created waterlogged conditions in some of the orchards, increasing the threat of root rot. As a result many of his growers delayed their normal mid-May first irrigation until early June.
“Walnuts can be touchy in heavier soils, and we didn’t want to start too soon,” Walkers says. “Most waited until the soil profile showed good root activity and the weather warmed, allowing for better growing conditions.” The later irrigation start also saved some pumping costs, he says.
The cool spring weather also 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.”
Walker has been a PCA for three decades. “I’ve been doing this long enough that not much in the orchards surprises me anymore,” he says. “Every season is interesting and generally has something for us to learn from.”
Some of the orchards he works with are fairly isolated in the eastern foothills. As a result, many walnut blocks there have very low codling moth pressure. Others, where there are moderate to high populations of codling moth in more-susceptible varieties, like Tulare and Vina, require more attention and monitoring.
“In the moderate to high pressure blocks, the codling moths have to be knocked down to maintain the highest quality of nuts possible,” Walker says. “This year, by late June, we had little or no activity in some ranches. In other locations, codling moth was very active in the 1A flight and 1B flight windows.” This year he treated one orchard earlier than normal.
In the last few years, codling moth numbers have been pretty high during the first flight. “That orchard has some early varieties,” he explains. “The moth counts during the first 1A flight were high enough that we wanted to treat it early to see if it would help reduce numbers in the second generation.”
In this case, Walker used two softer materials, with the idea of avoiding early mite and aphid treatments by protecting their predators from broader spectrum pesticides.
With the cool spring and early summer temperatures, web-spinning mites have not been a threat to date. Usually, his growers treat the mites in the early part of July, combining this pesticide with the codling moth spray to save money.
Husk fly traps will be going out early this month.
“In my walnut blocks, we usually have not had pressure from walnut husk fly until early August,” Walker says. “But, it’s a very unpredictable insect pest. Sometimes, it can start emerging the first part of July, so we have to be ready. Knowing a block’s history, timely trapping, and consistent monitoring helps keep the grower and consultant out of trouble.”