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Gardeners bracing for beetle attack
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ITHACA, N.Y. - Gardeners and landscapers across upstate New York and in neighboring states are bracing this spring for another onslaught from viburnum leaf beetles. The beetles attack several species of native viburnums - important shrubs and small trees found in woods and old fields - as well as many cultivated varieties grown in landscape plantings.
In late April or early May, just as the shrubs' leaves are emerging, the voracious beetle larvae hatch from eggs laid in the twigs last season. Where infestations are severe, hoards of tiny larvae (only about 1 mm long when they emerge) will often completely strip the plants. They grow to about one-half inch long before dropping to the ground to pupate.
Adults re-emerge from the soil in summer after damaged viburnums have grown new leaves. The quarter-inch beetles dine on the foliage of those plants or fly off to feed on other viburnums. Repeated defoliation for two or three years usually kills the shrub.
"That one-two punch - first the larvae then the adults - is really hard on the plants,"
says Lori Bushway, Senior Extension Associate in the Department of Horticulture, Cornell University. The best defense against the beetles, she adds, is to prune out the egg-laying sites anytime from fall through spring until shortly after the larvae emerge. The sites look like a series of 1- to 2-mm bumps in row along young twigs.
For the last two years, Bushway has been working with more than 335 "citizen scientists" from 20 states, 3 Canadian provinces and 24 counties in New York to track the spread of the beetle. They visit her Viburnum Leaf Beetle Citizen Science website to report beetle sightings and what species of viburnums are being attacked in their region.
You can also visit the website (www.hort.cornell.edu/vlb) to view pictures that will help you identify beetle egg-laying sites, larvae and adults, find out which viburnums are most resistant to beetle attacks, and learn other ways to minimize damage. For more information about the project, contact Bushway: ljb7@cornell.edu or 607-255-5918.
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