April 18, 2001 | By: Laura Skillman

Controlling San Jose scale is becoming an increasing problem for fruit tree owners in Kentucky.

The insect not only has a detrimental effect on the cosmetic look of the produce but also on the health of the trees, said Ric Bessin, University of Kentucky Extension Entomologist.

"It potentially kills trees," he said. San Jose scale is a sucking insect that injects a toxin into the plant as it feeds causing localized discolorations. The presence of reddish blemishes on fruit at harvest indicates a potentially damaging number of the insects on the trees. Left uncontrolled, San Jose scale can kill an entire tree in a couple of years.

The scale was brought into the country from plant materials from the Orient and was first found in the San Jose Valley of California. In the 1920s, San Jose scale killed sections of orchards in Kentucky and across the United States before being controlled by insecticides.

Today, there are limited insecticidal tools to control it, but some work well. Bessin said the best program for preventing scale damage is to spray with a dormant oil in early spring. The dormant oils can provide about a 95 percent control, he said. Dormant oils also have less risk to beneficial insects and to the person applying the spray.

In the last week of May or first of June, Bessin suggests that growers then use an insecticide to control the crawlers. Sprays directed against crawlers also protect fruit from infestation. Sprays should be timed about one week after the first crawlers are seen.

If populations are heavy, a second application two weeks after the first should be used. These applications aimed at the crawlers have little effect on the adult scales. Because San Jose Scale occur on all parts of the tree, spray coverage is very critical to effective control.

For more information on controlling San Jose scale on fruit trees, contact your local office of the University of Kentucky Cooperative Extension Service.


Ric Bessin, (859) 257-7456