Experts advise about cantankerous cankerworm

May 18, 2007|By Dan Lamothe | Dan Lamothe,Sun Reporter

For Steve Watkins, the questions about cankerworms have become a rite of spring.

How should he go about eradicating the pests infesting his tree nursery in Pasadena? How much time and effort should go into it? And, what should he tell his customers, who visit Himmel's Farm & Garden Center looking for solutions to the problem?

"There's only so much you can do with a 12-ounce bottle of insecticide," said Watkins, who has watched the insects at his two-acre nursery eat the leaves on everything from dogwood to hickory trees.

"We usually tell people to call professionals and get help."

Watkins' business sits in the middle of what etymologists and state officials call a stronghold for the cankerworm, which can defoliate hundreds of acres of trees when conditions are right. Infestation has been known to happen two years in a row. It is somewhat of a rarity for the area's trees to be under attack for the third straight year.

"Typically, they're kind of like phantom pests," said Robert H. Tichenor Jr., chief of the Department of Agriculture's pest management program. "They're notorious for popping up, stripping trees on thousands of acres of land and then disappearing."

Evidence suggests that the cankerworm has damaged trees this spring in several areas of northern Anne Arundel County, including Pasadena and Lake Shore. They have been reported in several locations they have not been seen in recent years, like near Ritchie Highway in Pasadena, and have caused heavy damage in areas near Chelsea Beach and Laurel Acres and along Lake Shore Road, Tichenor said.

Cankerworm infestations are usually not considered a serious concern because they attack trees early in spring, before leaves have matured. With many of the same areas affected for a third straight year, though, Tichenor said some trees are becoming "extremely stressed," and more susceptible to potentially fatal diseases and fungus infections.

"It's kind of like people dying from pneumonia," Tichenor said. "The germs for it are everywhere, but if you're already weaker from having something else, it's a lot easier to get it."

Michael J. Raupp, an etymologist at the University of Maryland, College Park, said trees can typically sustain defoliation to at least 25 percent before they start to suffer.

"They have an inherent ability to withstand these types of attacks," Raupp said.

Tichenor said the state recorded 6,082 acres in Anne Arundel County with cankerworm problems in 2006, more than triple the 1,608 acres recorded in 2005.

Raupp said the infestation in Anne Arundel County is uncommon because pathogens and parasites that kill cankerworms have not done enough to control their population.

"For some reason, Mother Nature's natural defenses are inoperative in that area," said Raupp, who has visited the Pasadena area the past two years to study the infestation and was returning this week. "This is not the norm, and one of these years, the natural enemies are going to catch up and you're going to see a natural decline in their population."

The problems are perpetuated in part because cankerworms spend nearly their entire lives in oaks, maples and other trees and shrubs consuming leaves, and reproducing so their young can follow suit. Young larvae tend to make holes in leaves, Raupp said, but the adults eat whole leaves.

In some neighborhoods, the problem is compounded because the same trees are also under attack by forest tent caterpillars and gypsy moths, Raupp said. All three are considered a menace to foliage, although gypsy moth infestations tend to get the most attention because they defoliate trees in June, when it is more damaging because of the dry summer season.

Raupp said little can be done to predict where cankerworms will strike, since their eggs are laid high and out of view in treetops, where they cannot be spotted from a helicopter -- a vast difference when compared to gypsy moths, whose large egg masses can be seen easily.

In the end, Raupp and Tichenor preach patience when it comes to dealing with cankerworms, especially since the season in which they cause the most trouble is expected to end sometime next week. They'll trek down to the ground on messy silk-like strands, then burrow into the dirt to make a cocoon and disappear until next spring.

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.