Now is the time to inspect mugho, Scots, red and other pine trees and shrubs for clusters of defoliating gray-green "worms."
The European pine sawfly is a common problem during the month of May. Larvae of this widespread pest are grayish-green with 2 light stripes and 1 dark stripe on each side of the body. The legs and head are shiny black. Full grown larvae, usually present by Memorial Day weekend, are about 1 inch long.
European pine sawfly larvae are gregarious and stay together in a cluster as they feed on the old needles from pine trees and shrubs. Because only old needles are eaten and not the new, emerging growth, defoliated trees are generally not killed. Damage may be aesthetically displeasing, especially in Christmas tree plantations, and growth of the tree may be stunted.
Control can be as simple as pruning off and discarding infested branches. Heavier infestations on larger trees may justify foliar sprays of horticultural oil, insecticidal soap or a contact insecticide such as Sevin. Spraying is of greatest benefit when done before the larvae become one-half grown. Late sprays, after larvae are full-grown, are usually not warranted.
This article originally appeared in the 5/4/2005 issue.