The Squash Bug (Anasa tristis) is a common pest on squash and other plants in some areas. They can be very challenging to control, and different insecticide products may target different life cycle stages (eggs, nymphs, adults) and not affect the pest at the other life cycle stages. For this reason, predicting when different life cycle stages will occur, based on current observations and weather data, can be very helpful. Researchers have developed a growing degree day model for Squash Bug to help predict when different life cycle stages will occur.

Calculating Growing Degree Day Units

The Squash Bug growing degree day model uses a lower threshold of 58.03 F and an upper threshold of 91.94 F for calculating growing degree day units. The growing degree day units can be calculated from daily maximum and minimum temperatures using these thresholds, or by using the Pest Prophet app, which features this model and is easy to set up and use.

Setting the Biofix date

In order to begin growing degree day accumulation, first a “biofix” date must be set which is the first date, after which growing degree day units will begin to accumulate. In the Pest Prophet app, the biofix date can be adjusted for any observed life cycle stages.

For the Squash Bug model, the biofix date should be set when the first generation of adults, or eggs are observed. Nymphs will occur at approximately 194 GDD(F), these can be targeted by insecticide treatment. At approximately 747 GDD (F) after the biofix, the next generation of adults will be observed.

Sources:

Fargo, W. S., and E. L. Bonjour. 1988. Developmental rate of the squash bug, Anasa tristis (Heteroptera: Coreidae), at constant temperatures. Environ. Entomol. 17: 926-929.