In orchards that did not receive a dormant peach twig borer treatment, UC IPM guidelines base timing of Bt bloom sprays on monitoring  the larvae emerging from over-wintering hibernacula – sawdust- or frass-covered cells bored under the thin bark of limb crotches or on tree trunks.

Most hibernacula are commonly found in the crotch of 2- to 3-year-old wood.

Usually, spring sprays are not needed for peach twig borer if a dormant spray or the series of Bt bloom sprays has been successful, or there is no history of peach twig borer problems. Otherwise, it may be necessary to using pheromone trap counts, shoot strike numbers, and degrees days to determine the best timing of a May spray.

“It all starts with a good program of monitoring your orchards and keeping accurate records to keep an eye on population levels and the amount of damage the pest causes,” says Kris Tollerup, UCCE IPM advisor, based at the Kearney Agricultural Research & Extension Center in Parlier.

Tollerup recommends placing pheromone traps in orchards at the rate of one per every 20 acres or at least two traps in smaller orchards by March 20 in the southern Central Valley, and April 1 in northern areas, and monitoring the counts twice a week.

Also, monitor trees for shoot strikes in mid-April. These are a part of a twig that wilted after being mined by peach twig borer or oriental fruit moth larvae. This can cause the affected portion of the twig to wilt. Shoot strikes are easiest to see on young trees and on water sprouts.

Look for larvae to distinguish between damage caused by peach twig borer from that caused by oriental fruit moth. To find the larvae, cut the shoot lengthwise. Oriental fruit moth larvae are white or pink with a brown head, while peach twig borer larvae are dark brown with white portions between each body segment and a black head.

Also, peach twig borer shoot strikes occur earlier in the season than do oriental fruit moth strikes.

 If the number of shoot strikes indicate treatment is necessary, use trap catches and degree days to determine when to make a May spray to target first-generation larvae. Optimum time is between 400 to 500 degree days after the first male is trapped in April.

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Accumulate degree days for peach twig borer using a lower threshold of 50 degrees Fahrenheit (F) and an upper threshold of 88 degrees F.

Keep in mind that applying broad-spectrum insecticides in May can cause outbreaks of secondary pests. However, softer pesticides including spinosad (Entrust, Success), spinetoram (Delegate), chlorantraniliprole (Altacor), and flubendiamide (Belt) can have a lesser impact on natural enemies, Tollerup notes.

If both peach twig borer and Navel orangeworm are present, a well-timed May spray can help to manage both pests, he adds.

More information on managing peach twig borer, plus tips for monitoring hibernacula and sheet strikes and using pheromone traps, is available online at www.ipm.ucdavis.edu/PMG/selectnewpest.almonds.html.