Bark beetles: coming to a pine tree near you

LWith the early season, unusually warm weather and lack of rain, expect to see significant bark beetle problems this spring and summer, at least if you are located in the northern and central part of the state.

If you have cut red, jack , Scotch or white pine piled in a pine stand or within 1/4 mile of a pine stand, it is recommended that you get it out now. If you had plans for summer cutting, thinning or pruning you should reconsider and decide if you really need and want to do it this summer. It is a lot easier to prevent a bark beetle problem than it is to control one once it gets stated. With the fire hazard, burning of bark beetle infested material is going to be very difficult. If we start to get adequate rains you may not have any trouble but if the drought continues you could have real problems.

Editor's Note: Is the droughty weather over in the northern counties? Recent rains are helpful, but we'll wait and see how the rest of the growing season goes. See the rainfall map. Typically, in northern Minnesota there is a shortage of moisture for trees in July and August.

In normal years there are two generations of bark beetles per year in Minnesota. This year there should easily be at least three, full generations. Bark beetles are able to develop large populations rapidly. In Itasca State Park, it was estimated that a single ten inch diameter red pine can produce close to 250,000 adult beetles in one growing season. So it doesn't take much brood material to produce a lot of beetles.

Adults began emerging from the duff layer where they overwintered around April 25th in Itasca County. To the south, they started even earlier. The beetles are now looking for suitable brood material and laying eggs. The eggs will hatch and larvae develop and feed in the moist cambium and, depending on temperatures, change to a new generation of adults in four to five weeks. So depending on where you are in the state, the next generation could be emerging from trees by mid- to late May. You need to get beetle infested material, greater than two inches in diameter, out of the woods and disposed of before that happens.

Methods of treatment and disposal are listed below:

    a. Haul the log decks to the mill, hopefully at least ¼ mile away from other pine stands.

    b. Peel off the bark. It's OK to keep the wood.

    c. Burn the slash and wood at least enough to char and destroy the bark (this is not an option if fire season continues and burning permits are not available).

    d. Bury the slash and wood.

    e. Chip the slash and wood. Chips can remain on the site or be used as mulch.

    f. Cover and seal the slash and wood with a tarp or heavy plastic until fall. Dig a trench around the pile, drape the edge of the tarp in the trench and backfill the trench. Be sure the tarp does not rip or get blown off.

    g. Insecticides are not effective and are not recommended.

Suitable brood material is any wood with bark attached and a creamy white cambium (inner bark) that is moist. This includes standing live trees stressed from drought or mechanical injury, trees with partially killed crowns from beetle activity last year, or wood cut over the winter that has not yet dried out. Trees killed by bark beetles last year usually pose no threat this year since the cambium is usually not suitable for breeding sites. However, some large trees killed by bark beetles feeding in the crown last year , have a bottom log that is still nice and moist and is suitable brood material this year.

So dust off your bark beetle literature from past droughts and refresh your memories. If you need further assistance contact your nearest Forester.