Plum Curculio, also known as the plum weevil, is a common pest of stone fruits, such as plums, peaches, nectarines, and apricots. Plum Curculio adults are small, snout beetles that are about 1/4 inch long. They have a dark brown or black body with white spots and a curved snout. Plum Curculio larvae are white and legless, and they grow to be about 1/3 inch long. Plum Curcuulio damage to fruit is characterized by crescent-shaped scars and dimples. Infested fruit may also be deformed or drop prematurely. PC damage can reduce fruit yield and quality, and it can make fruit more susceptible to diseases.

Plum Curculio adults emerge from the soil in the spring and feed on young fruit. The females lay their eggs inside the fruit, and the larvae hatch and feed inside the fruit. The larvae eventually tunnel out of the fruit and drop to the ground to pupate.

First treatment is recommended at the time of petal fall and should continue at intervals of 10-14 days until egg-laying has ended. The Plum Curculio Degree Day Model, developed by researchers, and available on the Pest Prophet app, is a tool growers can use to time predict the ending of the adult egg-laying (oviposition) phase.

Initiating the Biofix

To properly use the model, the biofix must first be set. This is the date that will serve as the starting point for growing degree day accumulation. For this model, petal fall should be used for the biofix date, along with the start of treatment.

Growing Degree Day Accumulation and Treatment

After the biofix is set, growing degree day accumulation can begin, using a lower threshold of 50F. Calculating growing degree days can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. The oviposition / egg-laying phase ends at 308 GDD (F). After this, the window for recommended treatment has closed.

Source:

Baskerville, G.L. and Emin, P. 1969. Rapid Estimation of Heat Accumulation from Maximum and Minimum Temperatures. Ecology. 50: 514-517.

Reissig, W.H., Nyrop, J.P., and Straub, R. 1998. Oviposition model for timing insecticide sprays against plum curculio (Coleoptera: Curculionidae) in New York State. Environ. Entomol. 27: 1053-1061.