Citrus Thrips (Scirtothrips citri) is a pest on citrus crops that can leave scars on the rind and cause economic losses in some areas.

Researchers have developed the Citrus Thrips growing degree day model, available on the Pest Prophet app, in order to help predict when different life stage events will occur, based on the weather.

Calculating Growing Degree Day Units

The Citrus Thrips growing degree day model uses a lower threshold of 58.2F 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 Citrus thrips model, in order to predict the emergence of second generation thrips, the biofix date should be set once the first generation has been consistently observed in the orchard. Approximately 125 GDD(F) after this biofix date, adult thrips will emerge and this is the optimum time for insecticide treatment.

For best results the biofix should be re-adjusted for each generation, based on scouting observations. This will improve accuracy of later crop stage predictions.

Sources:

Grout, T.G., J.G. Morse, N.V. O’Connell, D.L. Flaherty, P.B. Goodell, M.W. Freeman, and R.L. Coviello. 1986. Citrus thrips (Thysanoptera: Thripidae) phenology and sampling in the San Joaquin Valley. J. Econ. Entomol. 79:1516-1523.