Carpenter ants have been one of our most common and annoying pests during the past several years. Though we usually think of carpenter ants as a household pest, they are regularly encountered in the landscape as an "occupant" of trees.
Carpenter ants commonly nest inside older trees that are hollow or in trees that have dead limbs and branches. The nests are in rotted, decayed wood, although some nests may extend into sound heartwood in the center of the tree.
Carpenter ants in trees are not directly harmful to the tree. Control is not essential for the tree's health, as the ants are only taking advantage of an existing situation of soft, weak wood in which to establish their colony. Stress, mechanical injury, environmental conditions, disease or other insects are responsible for killing limbs or sections of the trees in which the ants are able to nest. Once injury has occurred, wood decay can set in if moisture is present; it is the wood decay that gives the carpenter ants the opportunity to nest in the tree. Carpenter ants use knots, cracks, holes and old insect tunnels to gain access to these areas.
Control of carpenter ants inside a tree may reduce invasion of the ants into adjacent structures. Insecticides labeled for use on trees in the landscape can be applied (dusted or sprayed) directly into the nest cavity. A treatment is not likely to permanently rid a tree of carpenter ants; retreatment every year or so may be necessary.
Plugging or sealing tree cavities or treating tree wounds with wound dressings is not advised. Such treatments are unnecessary and will not eliminate nor prevent decay or carpenter ant activity.
Cutting down an otherwise viable landscape tree in the hopes of avoiding ant problems in the home is not recommended. If a pest control company specializing in household insect control gives you recommendations about removing trees from your landscape, carefully consider the source of this advise. Check and double-check with qualified arborists before making drastic assaults on your landscape plantings.
This article originally appeared in the March 20, 1998 issue, p. 23.