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Wrap up cankerworm and defoliation problems

Gary Dymski | Home Work

July 21, 2005

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For most of May and the first half of June, they dropped in like unannounced houseguests, ruining virtually every outdoor activity. Many of my neighbors were forced into the middle of the street for their evening walks because these invaders had overtaken the low-hanging branches of trees that line the sidewalks.

You remember those tiny green worms that fell into your hair, onto plates of food and furniture on the patio. They seemed to be everywhere and on everything.

They were cankerworms. And while in the past few weeks they have moved out of the trees - and out of our hair - they're likely to be back again next spring. And they'll probably make outdoor life miserable again.

"We got a lot of phone calls from homeowners this year, more than probably the last couple of years," said Tom Kowalsick, a horticultural educator with the Cornell Cooperative Extension of Suffolk County. Although it seems that no one takes a census of the squiggly things, the calls seem to indicate there was something of a cankerworm population boom. These sorts of insect invasions run in cycles, Kowalsick said, so there's a good chance they'll be back next spring.

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What can you do? If you're an outdoors lover like me, you know how frustrating it is to have even one precious spring day ruined. But I'm also a homeowner who doesn't especially like to spread around insecticides and chemical sprays.

But there are environmentally sensitive ways to take preventive action, - such as using Tanglefoot, a glue-like tree wrap, and spraying horticultural oils that kill eggs in branches.

But no method is foolproof. "The key word to emphasize is may," Kowalsick said. "Whatever is done may reduce the population in your trees and in your yard."

There's plenty of time before we have to start wrapping trees and spraying oils. So now is a good time to learn a little about cankerworms and how they get into trees in the first place.

From early spring to about mid-June, eggs hatch in trees and feed on leaves. Beech trees, elms, hickories, maples and oaks are especially susceptible. Feeding can be so fast and furious that an entire tree can be defoliated. As the worms grow, they drop from the trees on silken-like strands. That's when they really get into your hair - not to mention your potato salad and iced tea.

When full grown, the worms enter the soil, where they pupate. In November and December, they emerge as moths. Males have wings; females are wingless. These wingless females continue the cycle by crawling up trees in the late fall to lay their eggs.

That's when it's time to fight back. Tanglefoot, a horticultural glue available at Agway and farm or garden supply stores, traps female moths as they try to climb the trees.

It's best to use Tanglefoot in late November or early December, depending on when the moths appear. The substance shouldn't be applied directly to the tree because its oil can be absorbed by the bark. Instead, the product should be applied to a tree wrap, which is an inexpensive waterproof paper about 3 inches wide that gets positioned around the bottom of the trunk. A 50-foot roll costs about $5.

If you can't get out in the fall to apply glue and tree wrap, spraying with a horticultural oil in the spring may - remember Kowalski's caveat - kill eggs. Oil is applied with a hose-end sprayer, and as it coats leaves and branches, it smothers eggs. Some products use plant-derived oils, but even the types made from highly refined petroleum oils combined with an emulsifying agent are considered environmentally friendly. Oils can be extremely selective; read the label so you select the right product for the right insect.

And, remember, timing is crucial. "You're going to have to go out, walk around the yard to see if eggs are in the leaves or if moths are crawling," Kowalsick said.

Of course, these products are not foolproof. Some eggs will survive the oil; some moths will escape the wrap. Even if a professional applies the oil, some sections of a tree can be missed, leaving eggs to hatch. "My guess is that you can reduce the number of worms you'll get," Kowalsick said. "But if you can't get great coverage, then you'll still have worms."

But a significant reduction could be enough to salvage some outdoor activities and perhaps even save a few young trees. Several weeks ago, one of my young red maples was totally defoliated by feeding worms. It has sprung back with leafy branches, but, Kowalsick says, the tree had to use extra energy to produce the new leaves. Over the long run, repeated defoliation can kill the tree or hamper its growth.

As far as I'm concerned wrapping and spraying are worth the effort. I'm going to do anything I can to reduce the worm population. If you're a hungry cankerworm, watch out. Come next spring. I'll be your Public Enemy No. 1.

A leaflet with tips for controlling cankerworms is available at www.cce.cornell.edu/suffolk /grownet/tree-insect/cankworm .html.

Visit Tanglefoot.com for pest-control products from the Tanglefoot Co., a Michigan-based manufacturer of environmentally friendly lawn and garden supplies.