Birch trees under attack

Sawfly causing damage to peninsula forests

Posted: Thursday, September 21, 2006

 

  Janice Chumley of the Cooperative Extension Service displays a leaf scarred by the amber birch leaf miner. The invasive pest is making its presence known on the central Kenai Peninsula. Photo by M. Scott Moon

Janice Chumley of the Cooperative Extension Service displays a leaf scarred by the amber birch leaf miner. The invasive pest is making its presence known on the central Kenai Peninsula.

Photo by M. Scott Moon

Kenai Peninsula property owners who thought they would be fine because they have plenty of birch trees mixed in with their bark beetle-threatened spruce trees may be in for some bad news.

According to the University of Alaska Fairbanks Cooperative Extension Service office, amber-marked birch leaf miners Profenusa thomsoni that have plagued trees in the Anchorage bowl for the past 10 years, are making their way to the peninsula.

The U.S. Forest Service has discovered the birch leaf miner in trees near the Russian River, at Jim’s Landing, in Moose Pass, near Swan Lake in the Swanson River drainage, at Captain Cook State Recreation Area and along Skilak Lake Loop, said Janice Chumley, integrated pest management technician for the extension service.

The leaf miner, which is actually a sawfly, will not cause tree mortality, according to Chumley, as long as trees are kept healthy.

“An exotic that came from Europe in the 1900s, the leaf miner has nothing here to keep it in check,” Chumley said, adding it was first detected in this country in the northeastern states.

She said the sawfly is not a good flyer. It can’t travel more than 50 miles or so on its own, so it most likely made the trip to the Kenai Peninsula by way of people’s cars and recreational vehicles.

Property owners can spot leaf miner infestation by examining the leaves on birch trees.

“The upper surface of the leaf looks brown and blistered,” said Chumley.

The tiny sawflies’ larvae subsist entirely by eating the chlorophyll-producing, or inner cells of the leaves.

If held up to the light, tiny black specks inside the leaf can be seen with the naked eye. The specks are actually digested plant material.

People can take a number of steps to help control the leaf miner population if it is detected, according to Chumley.

“Very simply, they can rake up the leaves,” she said.

The larvae exist in the leaf, and when raked up and disposed, the larvae in the leaves will not be able to over-winter in the ground and hatch in the spring.

“The best thing to do is keep your trees healthy,” Chumley said.

She recommends deep watering in early spring as the principle action for helping maintain a tree’s health.

Rock salt and other ice-melting products used on walks and driveways should be kept away from tree roots at the edge of the paved surface.

Tree roots also should be protected from being run over with lawn mowers and weed whackers.

Lastly Chumley advises people to prune trees only in the fall if at all. That gives the tree the entire winter season to heal over the wound, preventing insects from entering the tree.

Chumley also said certain chemicals can be used to control leaf miners, and people can call or visit the extension office on Kalifornsky Beach Road for a list. She can be reached at 262-5824.

A tiny, parasitic wasp is being used in the Anchorage bowl area as an experimental biological control of leaf miners, according to Chumley.

She said infested birch trees are being completely covered and the wasps, which are brought in from Edmonton, Alberta, Canada, are released under the cover to see if they can prevent leaf miners from over wintering.

In the mid-1990s, the wasp reportedly checked an amber-marked leaf miner infestation in Edmonton without any unintended problems.



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