With the almond harvest well under way and the walnut shaking likely to begin shortly, Tehama County tree nut growers in mid-August remain on alert for two major crop pests.

Navel orangeworm (NOW) is one. The number of eggs laid in traps this season has been running higher than usual. Warmer-than-normal weather this spring allowed more overwintering larvae to survive and generate bigger populations in the orchards this year. This points to an increased damage risk once the hulls split and the newly-hatched worms can get inside to feed on the nuts.

The next round of egg-laying is just around the corner and is likely to coincide with hull split in many orchards.

This season, egg-laying started about three weeks earlier than last year, reports Rick Buchner, University of California Cooperative Extension orchard farm advisor for the county.

He put this year’s first biofix– the beginning date of consistent egg laying – at April 11. Biofix for the second NOW generation was June 17, before hull split. The third biofix was on July 22, after hull split began. Unless treated with an insecticide then, any susceptible varieties of almonds going through hull split face a higher risk of damage and a lower market value.

He estimates the next Tehama County biofix will occur around Aug. 23.  Once laid, eggs usually start hatching about 100 degree-days or five calendar days later.

“Growers are watching NOW numbers fairly carefully,” Buchner says.  “At this point in the season, a rapid, early harvest is the best defense against worm damage and is an essential practice to preserve nut quality and optimum value. Growers whose crop is ready will start harvesting as soon as they can and go as quickly as they can to reduce exposure time to the worms.”

Reports of problems controlling walnut husk fly at various locations throughout the state have ramped up local grower interest in that pest, as well.

“There’s a lot of interest, but we haven’t seen much in the way of trap counts in the walnut orchards we monitor,” Buchner says. “So far the walnut husk fly catch has been relatively small, about the same this year as last year, in our test locations. However, every orchard is different and must be monitored, accordingly.”

Walnut husk problems likely reflect the difficulty of accurately monitoring walnut husk fly numbers and timing the first and additional sprays, he notes. The insecticide kills adult flies when they consume the material as part of a baited spray.

“Once the female has stung the husk to lay eggs inside, it’s too late to spray for those maggots.” Buchner says. The husk fly overwinters in the soil. If not properly controlled, it will return the following year in greater numbers.

This report is from Tree Nut Farm Press, a twice-monthly electronic newsletter published by Western Farm Press during the growing season. If you would like to receive Tree Nut Farm Press, see here for sign-up.

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