The Daily Globe - Serving Gogebic, Iron and Ontonagon Counties

Michigan DNR advises spraying to fight spruce budworms


June 9, 2016

Submitted photo

DEFOLIATION FROM spruce budworm caterpillars browns the needles of infested trees, as is evident in this Michigan Department of Natural Resources photo of a tree stand.

Michigan Department of Natural Resources forest health experts anticipate widespread defoliation from spruce budworms to continue across much of the Upper Peninsula in the weeks to come.

Robert Heyd, MDNR Forest Health Management Program leader, toured the region last week. He said the trees have shed their bud caps and spruce budworm larvae are feeding on the young spruce and fir shoots.

"Homeowners interested in protecting landscape spruce or fir from defoliation this year should spray trees now," Heyd said.

Products with Bt, a safe, soil-dwelling bacterium that is toxic to many insect pests, are recommended for spraying. Only one application is necessary.

"As the budworm larvae grow, they will cause increasing levels of defoliation," Heyd said. "Clipped needles will turn brown later in June, showing this year's affected areas."

Balsam fir is most severely damaged by budworms. During Michigan's last outbreak, two-thirds of the balsam fir and roughly four in 10 white spruce trees were killed.

Budworms also feed on black spruce, tamarack, pine and hemlock trees when they are in stands with balsam fir or white spruce, but those species generally suffer less damage.

Repeated budworm defoliation can cause top kill and tree mortality in older and stressed trees. Balsam fir older than 60 years and spruce more than 70 offer prime infestation opportunities.

Younger trees infested with spruce budworms lose much of their new growth, but generally survive.

Stands defoliated for more than a year can have heavy mortality or may have trees with dead tops, Heyd said.

In 2014, many areas in the western U.P. were defoliated for the first time, while other areas had been hit off and on for several years. Spruce budworm damage was much more widespread last year and varied throughout the region, Heyd said.

"Periodic budworm outbreaks are part of the natural maturation cycle of balsam fir and white spruce. Every 30 to 50 years, large-scale outbreaks cause widespread top kill and tree mortality," he said.

The last outbreak in Michigan started in the U.P. in the late 1960s and ended in the early 1980s. Spruce and fir mortality was mapped across 519,000 acres in Michigan.

For more information, check out a Frequently Asked Questions page on the spruce budworm on the DNR webste.


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