Gypsy moth are known to feed on many of woody plant species. The preferred species in Bucks and Montgomery County are oak, willow, linden and hawthorn. Shot holes in leaves beginning in spring may result in partial or complete defoliation by midsummer. The crowns of these trees will be thin initially and partially to completely defoliated under heavy pest pressure. The white, 1 1/2" long, webby egg masses can be found on trunks and limbs. These eggs hatch and larvae emerge as oak leaves begin to unfold in the spring of the year. The young larvae feed in April and May. The mature caterpillars, which grow up to 2 inches long and have five pairs of blue spots and six pairs of red spots in rows across their backs, feed in spring and summer. Caterpillars pupate early to mid-summer. The pupae are tear-drop shaped and brown. In summer, hair covered egg masses are laid in crevices, under picnic tables, and on vehicles, where they will overwinter.
Heavy pressure from gypsy moth has the potential to cause mortalities on shade trees, especially in stressful urban sites where gypsy moth feeding is coupled with stress from abiotic factors. Healthy trees can tolerate a single defoliation event; however, multiple defoliation events can cause dieback and decline even on healthy trees. Mortalities on stressed trees can occur after a single defoliation event. Threshold levels of gypsy moth are assessed by using egg mass counts in the winter months and can be used by arborists to help make decisions about treatment. While aerial sprays with Bacillus thuringiensis cannot be counted on to provide acceptable levels of control on individual high value urban trees, it is a tool for managing Gypsy moth infestations in locations where large numbers of susceptible tree species are growing in remote locations. Depending on the size and location of the trees to be treated, properly timed soil or trunk injected insecticides will provide predictable protection during high pest pressure.
Contact Plant Health Solutions for proper diagnosis and to develop a treatment plan.