Tree defoliators capable of serious damage are usually sporadic in nature and only cause noticeable damage in certain years. Attacked trees may be partially or completely defoliated. Pines and other softwoods can be killed or seriously weakened with one defoliation. Hardwoods usually recover following repeated light defoliation but successive heavy defoliations result in extreme growth loss and mortality.
Light defoliation (less than 20% ) normally will not affect the overall health of the tree, but moderate to severe defoliation will reduce growth. From 70%-100% reduction in diameter growth often occurs with two or more consecutive seasons of moderate to heavy defoliation.
Pines weakened by defoliation are made more susceptible to attacks from bark beetles, particularly the Ips engravers.
Hardwoods weakened by repeated defoliations are subject to attacks from various wood borers, ambrosia beetles and diseases like hypoxylon canker (on oaks).
Damage from defoliating insects to forestry production in Georgia is of minor concern at the present writing. However, periodic outbreaks of caterpiIlars such as the forest tent caterpillar, various sawflies and the oak leaf skeletonizer do occur and can attract considerable attention.
The oak leaf skeletonizer caused extensive damage to chestnut oaks in portions of Dawson and Pickens counties during the 1987 growing season. Bee keepers are sometimes affected when various caterpillers eat the flowers off of sourwood and other flowering trees before their bees can gather the nectar and pollen. Sourwood flowers early in the spring and is one of the first plants visited by bees. Moderate damage to sourwood flowers occurred in 1987 in portions of the north Georgia mountains.
The gypsy moth has not become established in Georgia at this time although male moths have been trapped in the state since the early 1970's. It is expected to be a serious forest and urban tree pest upon establishment.
Control of defoliators in Georgia has not been necessary under forest conditions. Christmas tree plantations and yard trees can be protected by applying a recommended insecticide (see appendix). Some common tree defoliators are illustrated in figures 24-35.