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May 15, 2003

Caterpillars munching on southern Indiana oak trees

WEST LAFAYETTE, Ind. – Two spring caterpillars with notorious pasts are causing noticeable damage in southern Indiana and are likely to cause problems there over the next couple of years.

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Cliff Sadof, a Purdue University Cooperative Extension Service entomologist, said linden looper and half-wing geometrid caterpillars are making a mess in several southern Indiana forests.

It's too early to tell if the caterpillars will cause severe defoliation, but Phil Marshall, forest health specialist with the Indiana Department of Natural Resources, said the signs aren't good.

"The caterpillars are so numerous at the moment that you can hear and feel their excrement falling from the treetops, and it's easily seen in the litter on the forest floor," he said.

Marshall said foresters have already reported defoliation in Jackson, Washington, Floyd, Perry, Harrison, Crawford and Clark counties.

At present, the loopers are one-half to three-quarters of an inch in length. Sadof said that while oak tree leaves are their main targets, they will eventually move to the leaves of hickory trees and other hardwoods later in the season. They will continue feeding until early or mid-June.

If defoliation becomes severe, commercial tree growers may notice a decrease in the growth of their trees.

"It's possible for trees to lose almost one-half inch in growth per year if they're severely defoliated," Marshall said. "If this sort of thing continues for several years, growers could face troubling harvests."

On the home front, Sadof said homeowners who live near wooded areas are likely to notice defoliation on their property, but at least 90 percent of the trees should survive the infestation.

Even though the caterpillars are numerous, Sadof said homeowners and foresters don't need to apply sprays to control them. Marshall suggested selective harvesting after the epidemic has stopped to manage the health of the forest and the effects of the loopers. He said it could take three to four years for the epidemic to stop.

"Maintaining tree health by providing adequate water is probably the most important action a homeowner can take," Sadof said. "Fertilization will not help defend a tree against these invaders."

As a last resort, the caterpillars can be killed with a single spray of a number of foliar insecticides, he said. However, early season application of some chemicals could cause problems with spider mites later in the season because of their ability to kill both the caterpillars and the natural enemies of the mites.

Sadof suggested spinosad or Bacilus thuringiensis sprays to kill caterpillars without causing mite problems.

While he is concerned, Sadof said it's important to remember that most trees are able to shrug off this pest.

"This isn't the first time these caterpillars have been in Indiana, so we know that most trees won't be killed by the defoliation they cause," he said.

Marshall said a similar outbreak occurred from 1979 to 1981. That outbreak reached from the Morgan-Monroe State Forest near Martinsville, Ind., through south-central Indiana to the Ohio River.

"After that infestation, areas of the forest that received repeated severe defoliations experienced 10 percent mortality of oaks and hickories," he said.

Writer: Kay Hostetler, (765) 494-6682, kjh@purdue.edu

Sources: Cliff Sadof, (765) 494-5983, cliff_sadof@entm.purdue.edu

Phil Marshall, (812) 358-3621, pmarshall@dnr.state.in.us

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

Related Web site:
Purdue Linden Looper Publication

 

PHOTO CAPTION:
The linden looper caterpillar is reappearing in alarming numbers in southern Indiana. The full-grown larva is about 1.5 inches long, bright yellow, with 10 black wavy lines running lengthwise down its back. The head is a rusty brown color. (www.forestryimages.org photo by John H. Ghent of the U.S. Department of Agriculture Forest Service.)

A publication-quality photograph is available at ftp://ftp.purdue.edu/pub/uns/sadof.looper.jpeg.


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