Despite this spring's aerial attack on cankerworms, City Arborist Don McSween is calling on Charlotte residents to band trees again this fall.
The effort was effective, but further spraying is not planned for the spring, making banding now even more important, he said. “That way, we can keep the numbers down and avoid having to spray as often,” he said.
Wrapping trees in sticky bands prevents the cankerworms from climbing up to lay their eggs.
Cankerworms are the caterpillars of a small native moth. They don't bother most evergreens, preferring instead deciduous hardwoods such as willow oaks, which they can strip completely bare.
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While healthy trees usually recover, trees weakened by disease, drought or repeated attack can die. In natural woodlands, cankerworms are present but rarely reach crisis levels.
In some areas, infestations have been so great in past years that in the quiet of nightfall, the caterpillars could be heard eating leaves in the treetops, growing larger every day.
Their excrement, tiny black grains, was thick enough to sweep on some streets and sidewalks. The silklike strands produced by the caterpillars clung to clothes, hair, windshields - just about everything.
The $1.1 million aerial spraying in April prevented widespread defoliation seen in past years. Using Bt, a naturally occurring bacteria that attacks only caterpillars, the application probably saved many mature trees weakened by drought, McSween said.
Aerial spraying is never 100 percent effective, however, said N.C. State University entomologist Steve Bambara.
Caterpillars that survived will mate this fall, and the wingless females will again crawl up trees to lay eggs in the uppermost branches. When spring arrives, those eggs will hatch, and cankerworms will once again begin devouring every leaf in sight.