Most of the time, termites don't attack living plants. The majority of subterranean and drywood termite species prefer soft, damp, dead wood that from a living tree. However, when a tree develops a disease or other weakness, these insects may move in. Formosan subterranean termites, a species relatively new to North America, are also less discriminating than other species, and will feed on live trees. Fortunately, there are a few things that can be done to discourage termites from attacking living trees.
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North American subterranean termites consume cellulose and occasionally feed on trees. The majority of these colonies eat only dead trees or the dead parts of live trees. These creatures nest in the ground and come out to attack the wood. It's wise to eliminate the food source by removing dead or diseased branches but avoid removing the whole tree, since this can leave dead roots in the ground. Examine trees regularly to make sure they stay in good health.
Drywood termites live inside the wood itself. They build colonies in dead tree limbs and trunks, but do not consume live wood. A related type, the dampwood termite, prefers moist, dead wood, but still does not eat the relatively firm wood of live trees. Any tree containing a colony of drywood termites is likely to be diseased or partially dead. Keeping trees in good health and removing dead limbs immediately can discourage these creatures. Unlike subterranean termites, these species do not live outside the tree, so getting rid of the colony should eradicate the infestation.
Formosan subterranean termites were first introduced to North America in the last half of the 20th century. These creatures originated in southeast Asia, and are much more willing to eat live wood than their North American counterparts. Formosan termites can hollow out entire trees and may be difficult to kill. Holes must be drilled in an infested tree above the soil line. Then termiticide can be injected into the cavity made by the termites.
In areas where termite damage to trees is a major problem, termite bait may be used. This anti-termite treatment works more slowly than conventional pesticides. Termites carry it back to the colony and share the bait with other termites. Eventually, most or all of the colony dies.
According to the United States Department of Agriculture, fungal foam may be appropriate for killing termites inside tree trunks and under bark. This fungus poses no danger to insects other than termites. The fungus grows inside the termites' bodies, eventually killing them.