Fall isn't early

Larvae responsible for falling birch leaves

Posted: Thursday, July 19, 2007

A lot of birch leaves curling up, turning yellow and falling off trees in the central Kenai Peninsula are not exactly an indicator of an early autumn this year.

The more likely cause is an infestation of the birch leaf roller, a species of larvae recurring throughout Southcentral and Interior Alaska, according to the U.S. Forest Service.

Birch leaf roller larvae, which feed on developing birch leaves, spin silk webs around young leaves, rolling them together to form feeding shelters.

Inside the rolled up leaves, the larvae skeletonize the leaves and frequently cause them to turn brown and die.

Once the larvae mature, they leave their leaf rolls and drop to the ground, pupate and emerge as small grayish brown moths in August, depositing eggs on birch twigs.

According to Curtis Stigall, an arborist working with the University of Alaska Fairbanks Cooperative Extension Service office, the birch leaf roller is peninsula-wide.

"Generally it's nothing to be alarmed about," Stigall said.

"If it turns around and damages a certain percentage 60 percent of your canopy, you might want to take a look at doing something for the tree," he said.

The forest service says leaf roller suppression is not warranted on forested land because they cause little permanent damage to the host tree.

While the roll-up defense makes treating the insect with topical insecticides difficult, Stigall said the defense is actually designed to protect the insect from birds or other insects.

The birch leaf roller is not known to have any specific predator, but Stigall said lady bugs, birds and some aggressive wasps "might go after it."

Although the effects of some tree pests such as birch leaf and aspen leaf miners can be reduced by raking leaves in the fall to remove over-wintering larvae, raking is not necessary with birch leaf rollers, according to Stigall.

"By fall, the insects are done," he said.

Tree specialists apply the one-third rule, he said: "If not more than one-third of the tree is affected, don't do anything."

In urban areas, where birch trees are planted in more isolated, artificial conditions, the birch leaf rollers can be more damaging, according to the forest service.

Homeowners should begin monitoring their birch trees in the spring. If people find rolled leaves, they should carefully unroll them and check for the green lead roller larvae. If no larvae are present, it's too late to control the larvae. Spraying with an insecticide would be ineffective.

Physically removing caterpillars can be effective on small trees when leaf roller numbers are small.

If trees are generally healthy and showing good growth, a few years of leaf rolling will not affect the tree's growth.

To keep trees healthy, they should be watered thoroughly once a week, especially during dry summer months, according to the forest service.

For more information on birch leaf rollers, residents can visit the Cooperative Extension Office on Kalifornsky Beach Road in Soldotna.

Phil Hermanek can be reached at phillip.hermanek@peninsulaclarion.com.

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