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New Mexico State University

New Mexico State University

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Watch for Tussock Moth Caterpillars on Evergreens

LAS CRUCES -- Hairy, tree-munching caterpillars may be blowing into parts of New Mexico during the next few weeks. These Douglas-fir tussock moth larvae feed on a variety of evergreens, said a New Mexico State University forest entomologist.

"Tussock moth larvae hatch in late May and early June," said Bob Cain, with NMSU's Cooperative Extension Service. "After hatching, they climb to the top of the host tree, dangle on long silk threads and ride the wind to new trees."

The caterpillars feed mostly on new growth of spruce, Douglas-fir and white fir, causing severe injury to landscape plants. "Damage from these insects has been reported in Santa Fe, Los Alamos, Raton, Ruidoso and the East Mountain area of Albuquerque," Cain said. New needles, especially near the top of the tree, can be completely stripped within weeks.

"The female moths have undeveloped wings and can't fly," Cain said. "They emerge from their cocoons, lay their eggs on the cocoons and cover the eggs with hairs from their bodies."

These hairs are severe allergens to some people. "When the caterpillars molt, they lose these long hairs," he said. "In large forested areas of California, where thousands of caterpillars molt at the same time, the hairs fill the air and often cause rashes on people working and recreating in the area."

In early June, homeowners should begin inspecting their landscape spruces and firs for tiny, black caterpillars chewing the needles into threadlike stalks. "In a few weeks, these will grow into colorful, hairy caterpillars with voracious appetites," Cain said.

Insecticides to control tussock moth are effective only when applied during early caterpillar stages. "Be sure to apply pesticides to the ends of branches and tops of trees where the caterpillars feed," he said.

The effects on trees attacked by Douglas-fir tussock moth can vary. They may be top-killed or completely killed, or they may recover. "Trees that were damaged last year can develop new growth on defoliated branches and may be fine in a couple of years," Cain said.

Give recovering trees extra water and fertilizer. Monitor these trees closely for the presence of new caterpillars this year, he added.