The Olive Scale (Parlatoria oleae) is a soft scale that causes economic damage primarily on olives, apples and pears. Severe infestations can reduce tree vigor and reduce flowering and fruit set. The Olive Scale Growing Degree Day Model can help to predict the timing of different life cycle stages.

Olive Scale Life Cycle Stages

Olive Scales overwinter as adults in twigs or branches, and adults emerge in late spring or early summer. Crawlers emerge later in summer and are active for a short time.

The periods of crawler emergence is key for insect prevention, if necessary. Researchers have created the Olive Scale Emergence Growing Degree Day Model to better predict when the adults will emerge.

Calculating Growing Degree Day Units

The Olive Scale Emergence Growing Degree Day model uses a lower threshold of 10C. It can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

Using Jan. 1st as a default “biofix” date, or starting point for accumulation. Peak crawler emergence / 50% of egg hatch occurs approximately at  716 GDD(F). This can be used an approximate target for beginning treatments.

For best results, the biofix date should be readjusted when adults are first observed. This will increase the accuracy for predicting later lifecycle stages.

Source:

Pinhassi, N., D. Nestel, and D. Rosen. 1996. Oviposition and emergence of olive scale (Homoptera: Diaspididae) crawlers: regional degree-day forecasting model. Environ. Entomol. 25:1-6.