Threecornered Alfalfa Hopper (Spissistilus festinus) is an important pest on on a variety of crops. Importantly, it can transmist Red Blotch in vineyards. Threecornered Alfalfa Hoppers typically overwinter as adults, (though sometimes as eggs) before emerging in spring. There can be 3-4 generations per year, depending on the location and climate. The Threecornered Alfalfa Hopper Growing Degree Day Model, developed by researchers, and available on the Pest Prophet app, is a tool growers can use to predict adult emergence in spring, as well as nymph and adult emergence of the following generations in a season.

Initiating the Biofix

To properly use the model, the biofix must first be set. This is the date from which growing degree days begin to accumulate. For this model, January 1st is the recommended biofix date, in order to predict adult emergence in spring, as well as larvae and adults of following generations.

Growing Degree Day Accumulation and Treatment

After the biofix is set, growing degree day accumulation can begin, using a lower threshold of 52F and an upper threshold of 100F. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. First overwintered adults will emerge and begin egg-laying at approximately 450 GDD (F). Late instar nymphs will emerge at approximately 1180 GDD (F) and adults at 1430 GDD (F) after the biofix date. Egg hatching / larvae emergence, and adult emergence of following generations can all be tracked using the model.

Source:

Wistrom, C., M.S. Sisterson, M.P. Pryor, J.M. Hashim-Buckey, and K.M. Daane. 2010. Distribution of glassy-winged sharpshooter and threecornered alfalfa hopper on Plant hosts in the San Joaquin Valley, California. J. Econ. Entomol. 103: 1051-1059.