-- Elm spanworms attack red and white oaks, and other species especially
Carya, (hickory, pecan and related trees) throughout the East. This
is a destructive forest pest, particularly in the southern Appalachians
where widespread, severe outbreaks have occurred. Repeated defoliation
can cause growth loss, dieback, reduction in mast crops, and mortality.
Insect (figure 1a). -- Larvae are slate grey to brownish black with
yellowish body markings (yellow or green at low population densities)
and 1.6 to 2 inches (40 to 50 mm) long. The adults are snow-white moths.
The olive green eggs are laid in masses on the underside of small branches
Injury (figure 1c). -- Young larvae feed on the edge and undersides
of leaves, causing a shot hole appearance. Later, they consume the entire
leaf except the main veins, leaving a feathered appearance to the tree.
-- Overwintering eggs hatch in early spring when the buds break, usually
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 to mid-July, the moths emerge and deposit their eggs. There
is one generation per year.
-- Insect parasites attack the eggs of the elm spanworm. Other natural
enemies also are important in keeping infestations in check. Chemical
controls are often needed to protect high-value trees.
Figure 1. -- (a)
Elm spanworm larva; (b) elm spanworm egg mass on branch; (c) defoliation
by elm spanworm.