The Obscure scale is a major pest of oak trees in many areas, and it can infect a variety of other trees. It is identified by its waxy covering which is mostly gray or black.

Obscure Scale Life Cycle Stages

Obscure Scales overwinter as nymphs in twigs or branches, and adults emerge in late spring or early summer. Males emerge first and then crawlers emerge later in summer and are active for a short time.

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

Calculating Growing Degree Day Units

The Obscure Scale Emergence Growing Degree Day model uses a lower threshold of 40F. 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. The first adult male emergence occurs at approximately 1093 GDD (F). Crawlers emerge at approximately 2738 GDD(F). This can be used an approximate target for beginning treatments.

Source:

Potter, D. A., M. P. Jensen, and F. C. Gordon. 1989. Phenology and degree-day relationship of the obscure scale (Homoptera: Diaspididae) and associated parasites on Pin Oak in Kentucky. J. Econ. Entomol. 82: 551-555.