Ash Borer (terminal borer)
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Importance
The ash borer is found throughout eastern North America. Spring feeding on tender shoots causes mortality of terminals resulting in forked trunks. When plantations are established to produce sawlogs, forked or deformed trunks are unacceptable losses. (This insect is also covered as a trunk pest in the insect borer section.)
Identifying the Insect
Tiny larvae found burrowing in terminals are white to yellowish with the dark gut visible. Larvae vary from 1.5 to 5.0 mm in length. After vacating the shoots, they feed elsewhere on the trunk and branches and may reach 34 mm in length. Adults are brown to reddish clearwing moths with a wingspan of 25 to 38 mm.
Identifying the Injury
The earliest symptom is a sudden wilting of succulent green shoots, which become shriveled and dark within 4 to 8 days. Tunnels are typically 1 to 3 cm long before the shoot is vacated. It takes less than 1 month for the terminal to wilt, darken, shrivel, die, and break away, often resulting in forked stems in new growth.
Biology
Adult moths begin emerging in March in the South and oviposit on the shoots and bark. Newly hatched larvae tunnel into the succulent shoots during April and May. In the South, shoot injury peaks by mid-May, declines in late May, and ceases by early June. Young larvae are present in the shoots for only 2 to 3 weeks; then they vacate the galleries and become trunk borers.
Control
Natural enemies help reduce borer populations. Insecticides may be necessary in new plantings, especially those surrounded by heavily infested ashes.
Gallery
 Photo by James Solomon, USDA Forest Service, Bugwood.org |
References
Solomon, J.D.; Leininger, T.D.; Wilson, A.D.; Anderson, R.L.; Thompson, L.C.; McCracken, F.I. 1993. Ash pests: A guide to major insects, diseases, air pollution injury and chemical injury. Gen. Tech. Rep. SO-96. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 45 p.
