A tiny, six-legged invader is threatening in some parts of the state a popular and widely planted ornamental shrub, and it’s apparently on its way here, according to horticulture experts.
The viburnum leaf beetle is native to Europe but was first seen in Canada in 1947 and has been spreading through New York for about 20 years.
Lori Bushway of Cornell University is part of a team tracking the beetle. She said the beetle has been tracked moving into the Hudson Valley and south into Ohio.
“Each year, from late June through early July, millions of the beetles are mating, which begins a cycle that can kill viburnum bushes in a year or two.” Bushway said.
The adult beetles measure about a quarter of an inch in length and a female can lay up to 500 eggs a year.
“[The beetle] is a voracious eater that can defoliate viburnum shrubs entirely. Plants may die after two or three years of heavy infestation,” she said.
Robin Wolfe, a perennial specialist at Wells Nursery in Schenectady, said the beetle has not yet been recorded in great numbers in the immediate Capital Region.
“It’s nothing we’ve been asked to diagnose yet,” she said.
Wolfe said the nursery often recommends property owners landscape with viburnum because there is a wide variety of types.
“They are a common landscaping shrub because they do well in shaded areas and they are hardy to our zone. They make a nice hedge,” she said.
She said nursery staff examine the plants they have before they are sold.
Sue Pezzolla of Albany County’s Cooperative Extension said the viburnum is appealing in any yard because of its three-season interest.
“They flower in the spring and bear fruit in the summer, which draws birds. In the fall, they have the most beautiful red, orange and yellow leaves,” she said.
On a recent outing to a local nursery, Pezzolla said she and a few other people were specifically looking for the beetle and found a few.
“It was interesting that the beetles seemed to be selective in what types of plants they wanted. The viburnums were lined up in three rows of each kind and the beetles would jump blocks of plants to get to the ones they wanted,” she said.
Arrowwood and small snowball varieties seemed the hardest hit, she said.
Viburnum tomentosum, which is one of the more common ones sold, did not appear as appetizing.
Sue Beebe at Cornell Cooperative Extension in Saratoga County said she keeps an eye out for the beetle at home and in the shrubs on county property.
“We have a huge population of viburnum at the training center and the county offices and I haven’t seen any [beetles] at all,” Beebe said. “One of our people is part of the Citizen Scientists project out of Cornell University and she saw a few back in 2004.”
She said weather does not seem to impact the population of beetles as they are most vulnerable in the egg stage and they adapt to cold temperatures.
Ruth Schottman of Burnt Hills is an area expert in wildflowers and a teacher for The Environmental Clearinghouse in Niskayuna. She was one of the first to spot viburnum leaf beetles locally.
“Last year and this year I have seen them on only arrowwood viburnum,” she said. “I saw them at a nature conservancy in Albany County and in the woods near Lake Desolation in Saratoga County.”
She said she reported the findings to Cornell University and was told the Lake Desolation discovery was the first in Saratoga County.
Dr. Paul Weston in the Department of Entomology at Cornell University said it appears the beetles reach peak infestation about three years after the first few are reported.
“We calculate the rate of spread is about 50 miles per year,” he said. “We had our first report of beetles in Schenectady County last year so they are likely in modest numbers there now and in two or three seasons will be substantial.”
According to Cornell’s Web site, viburnum leaf beetles only infest viburnums. Adult females lay their eggs on viburnum twigs in summer and early fall. The eggs hatch in spring, she said. Larvae feed on foliage until early summer, then crawl down the shrub and pupate in the soil. Adults emerge from the soil in midsummer, feed again on viburnum foliage, and mate.
The cycle from egg hatch to adult takes just eight to 10 weeks and can completely strip a plant of its leaves.
“A plant can tolerate being defoliated one year or even two, but it depends on the age of the plant and how strong it’s root system is,” Bushway said.
She said the best way to prevent the spread of the beetles and to save a plant that has been infected is to cut away all twigs that contain eggs in the early spring before the eggs hatch.
“Getting rid of the egg sites is the key,” she said.
Weston said at this point in the year only insecticides will stop the spread and the poison will have to be reapplied several times to kill the adult beetles.
“If you didn’t notice the eggs, it is likely too late to deal with the problem this time around,” he said.