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Plum Curculio and Peaches

Despite their name, plum curculio (PC) have a wide range of cultivated tree fruit hosts and can also survive on wild hosts such as hawthorn, wild plum, and native crabapple. It doesn't take long in a warm spring like we've had for PC to start wandering into orchards from their overwintering sites in hedgerows and bush areas. This year, PC were caught in traps on orchard edges over the weekend of May 6-7 and again on May 12; they may have been active even earlier. These small weevils will feed on leaves as soon as they emerge and will switch to blossoms and fruit as soon as they are present. Cosmetic damage from their feeding and oviposition (egg-laying) scars on fruit are a problem, but significant damage comes from the grubs (larvae) feeding within the fruit. With normally protracted emergence time in spring (2 to 6 weeks) and a long oviposition period (which can also extend 4 or even 6 weeks), grubs can still be present when fruit ripens.

Some PC activity occurs before the first oriental fruit moth spray in peaches. The current resistance management strategy for OFM in peaches with Lorsban (chlorpyrifos) for the first OFM spray has the added benefit of reducing PC in peach orchards. Lorsban is not labeled specifically for PC, but it does a good job of controlling them. However, depending on the temperatures after that first OFM spray, PC that were missed can continue to lay eggs in developing fruit for anywhere from 2 to 6 weeks.

The key to deciding if additional PC sprays are warranted is monitoring for new PC damage on fruit 7 to 10 days after application of Lorsban. Fresh damage shows green tissue in a characteristic crescent-shaped scar while older damage will callous over and turn brown. Older damage retains the crescent shape though, so diagnosing PC damage is relatively easy. If new PC damage is found only on the border of an orchard, a border spray is usually adequate. A variety of products are registered for PC in peaches (such as Guthion, Sevin, Zolone, and Imidan) and other products are registered for this pest in different fruit tree crops.

Plum curculio egg-laying scars on young apples are easier to detect than on peaches

Photo from 'Common Tree Fruit Pests' by Angus J. Howitt (1993).