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Caterpillars gang up on berry bushes, native trees

Mike Dunham
An autumnal moth caterpillar munches on alder leaves.
A Bruce spanworm moth is one of two species of geometrid moths defoliating vegetation on the Kenai Peninsula, Anchorage and Mat-Su areas.
Willows off Arctic Valley Road near Eagle River in August 2011 show the effects of geometrid moth defoliation.

The outlook for blueberries in Southcentral Alaska this year?

"It's quite bleak," says Michael Rasy, statewide integrated pest management technician for the University of Alaska Fairbanks Cooperative Extension Service.

The reason: two species of moths, the Bruce spanworm and the autumnal moth. Both are members of the larger family that includes what are popularly called loopers and inchworms and known to scientists as geometrid or geometer moths.

Native deciduous trees, as well as blueberry and salmonberry patches, have been damaged from the southern Kenai Peninsula to the Valley. A bulletin from the Extension Service on Tuesday noted one popular blueberry spot off Hiland Drive has been "denuded."

"There's just nothing there," Rasy said. "Everything is brown and bare."

The damage occurs within the 2,000- to 2,500-foot level in elevation, he said. "Around here, that's prime berry picking area."

It would encompass, for instance, favorite spots around Arctic Valley and Glenn Alps.

The infestation appears to have begun in the lower Kenai in 2009, quickly moving north. Eagle River homeowners with property that backs into the native landscape at those elevations were among the first to sound the alarm, Rasy said. "It's the second year that they've gone through a summer without greenery. It's looked like winter for two years in a row."

Berry leaves -- the bugs eat leaves, not the berries themselves -- are not the pests' first choice. Depending on their location, they seem to prefer small scrub birch, willow, alder or cottonwood. Such trees have borne the brunt of the assault. Rasy suspects that the moths have switched to berries because they've exhausted their preferred food.

"They're doing it out of desperation," he said. "But it probably won't sustain them. Caterpillars that feed on the blueberries will not survive."

The defoliated plants may look dead, but will survive unless the attacks continue for several continuous years, Rasy said. But these infestations tend to run their course within three years.

Nanwalek, at the southern end of the Kenai along Cook Inlet, caught the first season of infestation and "should see a marked improvement next year," Rasy said.

This season, the worst-hit spots include Eagle River, around Summit Lake on the Seward Highway, and near Homer and Seward, where, the Extension Service reports that "hundreds of trees have been defoliated." The northern Peninsula, Anchorage and Mat-Su will likely have another year or two of trouble.

The damage is done by the species when they are in the caterpillar stage. The crawling critters hatch in the spring and start devouring leaves. (Actually, they don't crawl so much as hump up then stretch out then hump up again; it gives them the appearance of measuring something, hence the name "geometer" from the Greek for "earth-measurer.") Around the end of June, they go into their pupa stage in the soil, emerging as moths in the fall.

Summer infestations by one insect species or another are not unusual in Alaska. But the fact that two types are hitting the same kind of plants in the same season is rare, said Rasy.

"To have multiple species going at one time like this is kind of unprecedented," he said. It's hard to predict how it will turn out. However, "I think a lot of this stuff will recover."

There's some good news in the wet weather of recent days. "The health of the plant has a lot to do with how it goes," Rasy said. "Right now we're getting a lot of rain, which is probably the best scenario for the plants."

Gardeners should make sure ornamental trees and berries are well-watered. An insecticide can also combat the pests, but it must be applied around the end of May and caution is advised. The Extension Service has information and recommendations.

As if the empty berry baskets aren't irksome enough, the pupae will turn into zillions of egg-laying moths in the next few weeks.

"Last year, there were clouds of flying moths everywhere," said Rasy. "On Hiland Drive they were so thick it looked like snow."

Those wanting to pick berries should head north, Rasy said. The caterpillars have not razed the crop there.

But for Anchorage and the Peninsula, "It may be slim pickings, for at least this year," he said. "We'll see what happens next year -- and hope for the best."

Reach Mike Dunham at or 257-4332.

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