Plum Curculio Movement into Orchards Will Begin Soon

Plum curculio adults typically overwinter in protected areas adjacent to commercial orchard blocks. In orchards not subject to weed / ground cover management, the pest may also overwinter within the orchard.

Movement in the spring prior to petal fall is highly dependent on weather conditions, and stretches of warm weather during the pre petal fall period are conducive to concentrated emergence and immigration back into the orchard. Likewise, cool temperatures during the pre petal fall period may lead to extended immigration. Expect emergence to begin where the mean temperature is 13-16 °C for 3 to 4 days, is above 16 °C for 3 days, or if over 24 °C, for 2 consecutive days. Moisture also plays a factor in triggering migration and appears necessary early in the spring for any plum curculio activity to take place.

The particular stage of crop phenology is apparently not a reliable predictor of the onset of immigration, because this may occur as early as silver-tip or as late as the first week of fruit development, depending on spring (and potentially even winter) weather. However, research in other areas indicates that in most years, the majority of plum curculio adults (57% to 70-8%) have already moved into orchards from overwintering sites before petal fall in apple.

Mating occurs in the spring, before fruit set. Females may be ready to lay eggs before the required fruit resources are available. When this occurs, they will simply hold their eggs, feed on green tissue and developing blossoms, and wait. In any event, there is little need to manage the population until oviposition begins following petal fall or in stone fruit, at shuck split.

In years with high pre petal fall temperatures, whole block sprays around petal fall should yield excellent control of the majority of the population. In cooler years, migration may be delayed and prolonged. Subsequent monitoring for any signs of new damage (difficult on some tree fruit) can help determine the need for reapplication of pest control products.

Growers now have several products available for managing plum curculio in apples and / or pear (including several organophosphates, carbamates, pyrethroids, neonicotinoids, Surround, and the naturalyte Delegate for suppression). We are still waiting for a comparable tool kit for use in stone fruit. Keep in mind that products vary in terms of their residual efficacy and mode of action / insecticidal activity (lethal, curative, antifeedant, repellent / oviposition deterrent). Some examples include the neonicotinoids with antifeedant and oviposition deterrent properties, and Guthion and the neonicotinoids with curative activity against larvae that are already in fruit.