Importance. -- The preferred hosts of elm spanworm are red and white oaks and a few other hardwood species, especially hickory, pecan, and related trees. This is a destructive forest pest, particularly in the southern Appalachians, where widespread, severe outbreaks have occured. Repeated defoliation can cause growth loss, dieback, reduction in mastcrops, and even mortality.

Identifying the Insect. -- Larvae are slate gray to brownish black, with yellowish body markings (yellow or green at low population densities), and l I/2 to 2 inches (40 to 50 mm) long. The adults are snowwhite moths. The small, barrel-shaped, olive-green eggs are laid in masses on the underside of small branches in the Southeast. To the north, they are found more commonly on the bole.

Identifying the Injury. -- Young larvae feed on the edge and undersides of leaves, causing a shothole appearance at low population levels. When populations are high, they consume the entire leaf, except the main veins, giving a feathered appearance to the tree.

Biology. -- Overwintering eggs hatch in early spring when the buds break, usually in late April in the South. The larvae feed for 4 to 6 weeks and then pupate in net-like cocoons on the host tree or understory. Six to 10 days later, in late June or mid-July, the moths emerge and deposit their eggs. There is one generation per year.

Control. -- Insect parasites attack the eggs of the elm spanworm. Other natural enemies are also important in keeping infestations in check. Chemical controls may be needed to protect high value trees.

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USDA Forest Service - Forest Health Protection, Southern Region
Last Modified: Monday, 14 January 2013 at 09:08:17 EST