The Potato Psyllid (Bactericera cockerelli) is a major pest on potatoes and tomatoes in many regions. It can damage leaves with its feeding and can also be a carrier for bacterium that causes Zebra chip disease in potatoes. After overwintering, they gather on newly formed citrus leaf buds where they feed and mate. Researchers have developed a growing degree day model for Potato Psyllid to help predict when overwintered adults will lay eggs, when nymphs will emerge, and when subsequent generations will happen.

Calculating Growing Degree Day Units

The Potato Psyllid growing degree day model uses a lower threshold of 40F and an upper threshold of 86F 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 Potato Psyllid model, the biofix date should be set to January 1st for the Northern Hemisphere. Approximately 163 GDD(F) after the biofix date (when eggs are observed), first overwintering adult egg-laying will begin, with the peak at 763 GDD(F). At approximately 1260 GDD(F) after the biofix date, the peak of F1 nymphs will be observed. At approximately 1045 GDD (C) the next generation of adults will be at peak egg-laying. Subsequent generations can also be predicted using the model, up to the F6 generation.

Sources:

Munyaneze 2012 Invited Review Article Zebra chip disease of potato: biology, epidemiology, and management. Am. J. Pot. Res. 89:329-350

Lewis, O.M., G.J. Michels, E.A. Pierson, and K.M. Heinz. 2015. A predictive degree day model for the development of Bactericera cockerelli (Hemiptera: Triozidae) infesting Solanum tuberosum. Env. Entomol. 44:1201-1209