During an Arbor Day ceremony earlier this year I talked about the importance of proper tree care in preventing insect pests and diseases. Young trees weakened by improper planting and watering are susceptible to numerous pest problems, the most serious of which are wood-boring insects.

Perhaps the worst pest of newly planted deciduous fruit and landscape trees is the flatheaded borer. These beetles often invade sunburned areas on the trunks of newly planted first year trees. The adult beetle lays its eggs on the injured bark, and the larvae bore tunnels beneath the bark. In most cases there is no external evidence that the borers are present. Later in summer, the invaded areas may crack and expose the tunnels, but by then it may be too late to save the tree. Feeding by the flatheaded borer larvae may kill a portion of the bark, weakening the tree, or may girdle the trunk and kill the entire tree.

The shothole borer, another beetle, may also be a serious pest of young deciduous fruit trees. This insect is a pest primarily in trees already weakened by root diseases, drought, sunburned limbs or flatheaded borer attacks. The adult female beetle bores beneath the bark of weakened trees to lay a number of eggs; the larvae hatch and begin feeding, creating an extensive gallery system in the tree's cambium and water-conducting tissues. As with the flatheaded borer, you probably will not realize the tree is being attacked until it's too late. The borers eventually mature and exit the tree as adult beetles, leaving dozens of tiny "shotholes" in the bark.

Both flatheaded and shothole borer adult beetles have by now exited the trees where they overwintered as pupae beneath the bark. Gardeners have been noticing trees with numerous small holes in branches and trunks, a sure sign, along with dying branches, that the insects are out and searching for new trees to infest.

The best way to avoid infestations of these pests is to keep your trees sound and vigorous. You can prevent sunburn, and flatheaded borer attacks, by painting the tree trunk from 24 inches above to 1 inch below the soil line with white, indoor latex paint or whitewash. When you prune young trees, leave a few small twigs along the trunk and major branches for shade. Train your young trees to avoid flat branches that catch the sun's direct rays, as such branches are more prone to sunburn.

The most important thing is to keep your trees properly watered. Dry trees are especially susceptible to sunburn and borer attack. Control weeds, which compete with your trees for water and nutrients. Healthy trees exude resin, which usually kills shothole borers before much damage can be done. This resin buildup does not develop in injured or weakened areas of the tree, allowing the borers to successfully invade.

On older trees, you may be able to save branches that have been attacked by flatheaded borers. Carefully remove loose and dead bark that covers the galleries, and destroy any larvae you find. Do not injure living tissues at the edges of the wound. Then, paint the area with white indoor latex paint to prevent further sunburn injury. Branches that are infested with shothole borers (look for numerous small holes, often leaking sap) should be entirely pruned out. If the rest of the tree is healthy and vigorous, you may be able to save the tree by pruning out the infested branches. However, if the tree is weak and declining, or if the trunk is infested with shothole borers, it's best to remove the entire tree.