Search this site:

Native Insect Pests of Hardwoods

Forest tent caterpillar

The forest tent caterpillar (FTC) (Malacosoma disstria) occurs throughout most of the United States and Canada, where it defoliates a variety of hardwoods (Batzer and Morris 1978, Fitzgerald 1995, U.S. Department of Agriculture Forest Service 1985b). In the South, it heavily defoliates water tupelo, sweetgum, blackgum, and various oak species. The most persistent and extreme outbreaks in the South occur in bottomlands, forested wetlands, and riparian areas. However, when FTC populations reach epidemic levels, the caterpillars often spread to urban and suburban areas where they defoliate a variety of shade trees and ornamental plants. Outbreaks in recreation areas may adversely affect business due to the nuisance created by migrating caterpillars and the presence of completely defoliated trees during the tourist season.

Outbreaks of the FTC occur in several Southern States, where well over 500,000 acres can be defoliated in a single season; FTC defoliation does not cause significant amounts of tree mortality. However, it does cause significant loss of tree growth. Repeated, heavy defoliation of stands may cause significant amounts of dieback.

Impacts of FTC occur mainly in the bottomland hardwood-cypress forest types (mapped as oak-gum-cypress and elm-ash-cottonwood), but they are occasionally a problem in upland northern hardwood forest types (mapped as maple-beech-birch, oak-hickory, and oak-pine). Most FTC defoliation occurs on forest lands that are not managed. Neither ownership nor intensity of management influences the impact of this pest. However, a number of chemical and biological treatments are available (Harper and Abrahamson 1979).

Future impacts of FTC on southern forests are likely to be much the same as in the past.

Hardwood borers

Insect borers are important pests of hardwood trees throughout the South. They tunnel in the bark, trunks, terminals, and roots, causing a variety of defects in wood, deformation of stems, reduction of seed production, and tree decline.

Some of the major damaging borers in the South are the carpenterworm, red oak borer, white oak borer, ash borer, poplar borer, oak timberworm, Columbian timber beetle, and ambrosia beetle (Solomon 1995). Borers, endemic to an area, do not normally cause dieback and mortality, but in abnormally large numbers they do contribute to tree decline. Severely affected stands can be seriously degraded. Excessive numbers of growth defects caused by borers are reported to affect between 25 and 88 percent of all hardwood logs. The most recent loss estimate available (based on timber values) is slightly more than $29 million in 1998.

Prevention and control of borers in living trees are difficult and often are not economically feasible. Nevertheless, there are several options available to managers. Chemical control of woodborers is feasible only for high-value trees. Synthetic sex pheromones, available for some borer species, are useful to survey and monitor borer populations, and to establish optimum timing for insecticide application. Silvicultural treatments and practices that favor good tree health, while slow to take effect, are the most enduring controls (Graham 1959). Silvicultural controls are based on the fact that intensively managed hardwood stands on productive sites generally sustain less borer damage than those with little or no management. Ownership, except as it may affect intensity of management, has no direct effect on the activity of borers.

Recently, prolonged droughts have caused a decline in the vigor of oaks across the northern portion of Arkansas. This decline has permitted the development of a massive red oak borer outbreak. While not the primary cause of the oak mortality being experienced in that area, the borers have proven to be the most destructive agent to date in the decline complex. They have reduced salvage value to virtually nothing due to the extensive damage they have caused to the wood of dead and dying trees.

Most of the major insect borers are endemic across the South and will continue to impact hardwood stands in the future. Atypically high populations of woodborers will continue to occur periodically.