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Poplar pests produce sticky puddles of goop

FLATWOODS -- Have the poplar trees growing near your home been dripping a sticky sap-like substance over your cars, flowerbeds or outbuildings?

 If so, don't feel alone.

It's proving to be a banner year in West Virginia for the tuliptree scale, an insect pest that digs its head into the vascular systems of yellow poplars, or tulip trees, and sucks out the sap.

The ground beneath a poplar infested by tuliptree scales soon becomes moist with sticky "honeydew," as the excrement produced by the pests is delicately known, and the sugary substance often attracts ants and wasps. 

"The dirt or pavement beneath a tree heavily infested by the tuliptree scale looks like it has recently been rained on," said Clint Ferguson, a forest health protection specialist for the state Department of Agriculture's Plant Industries Division. If the honeydew is not rinsed off, it produces a black, sooty mold that can be a chore to remove, as Ferguson has learned firsthand.

He recently parked his truck under an infested tree and waited too long to rinse off the resultant honeydew. "I had to scrub the truck with a de-greaser to get the mold off," he said.

State Department of Agriculture forest entomologist Tim Tomon said tuliptree scale infestations are an annual occurrence, but are generally limited to one or two areas within the state.

"This year, it's widespread, ranging from Parkersburg down into Raleigh and Mercer counties," Tomon said. "I've never had as many calls about any other insect in the three years I've been working here."

In central West Virginia counties like Braxton, Calhoun and Clay, where the tuliptree scale is most evident this year, "people are saying it's the worst they've ever seen it," said Ferguson.

What's the reason for this year's bumper crop of tuliptree honeydew?

"I think the warm winter had a lot to do with it," said Tomon. "There's normally a lot of winterkill with the tuliptree scale, and it didn't seem to get cold enough for that to happen."

The insect is called a scale because of its soft, waxy, scale-like covering that resembles a miniature turtle shell. When clumped together on a limb, the pests resemble scales on a fish. Colors range from grayish green to a pink-orange tint mottled with black.

Male tuliptree scales mature in late spring, and emerge from their scale coverings as tiny, two-winged insects that mate with females and then die. In August, the females lay eggs and give birth to nymphs called crawlers, which are able to move about their birth trees and are spread to new trees by the wind or by riding in the plumage of birds. If a suitable host tree is not found within three days, the crawlers usually die.

"The females each produce about 3,000 eggs, and since the sap from poplars doesn't have much protein, they have to eat a lot of it," said Tomon. "It's kind of like going through the summer having only Kool-Aid to eat."

By August, when the reproduction process moves into full swing, "the females are done with the honeydew-making," Tomon said.

Extreme infestations of tuliptree scales can cause branch dieback, discoloration of leaves and leaf loss in mature trees, and can sometimes kill young trees up to five inches in diameter. Trees that are stressed attract increased populations of the pest, so watering and fertilizing yellow poplars can decrease the likelihood of heavy infestations.

 Tomon said some homeowners are concerned that heavy tuliptree scale infestations will kill their mature poplars. "But it's normally not fatal to the larger trees - it's more a cosmetic problem than anything."

 When the pests are in their crawler stage from mid-August to mid-September, contact insecticides like malathion and carbaryl can be used to kill the insects, Tomon said. During the fall, he said, systemic insecticides, such as imidacloprid, can be injected into the soil around the base of the tree, where the poplar's roots will absorb them.

"But unless you're anticipating another really mild winter, I wouldn't recommend treating at all," Tomon said.

Another pest affecting the poplar this summer is the yellow poplar weevil, which chews unsightly holes in yellow poplar leaves. Weevil larvae that feed within leaf tissues in late spring can cause a scorched appearance on leaf surfaces. While the weevils may produce some leaf loss, they do not otherwise harm healthy yellow poplars, according to Tomon.

For more information on the pests, call the West Virginia Department of Agriculture's Plant Industries Division at 304-558-2212.


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