Help! My Scotch pines are falling over!

Pine trees weakened by pine root collar weevils may fall over and die one to four years after attack.

Each spring, we get calls from homeowners asking why their Scotch, Austrian or red pine blew over during the winter. The culprit is usually Pine Root collar weevil. Feeding by larvae weakens the tree at the root collar, eventually girdling and killing the tree. Trees are weakened at ground level and may fall over or die within one to four years of the first attack. When trees are girdled, the entire canopy fades from green to yellow to red. Larger trees that have been partially girdled have low growth rates and are more susceptible to windthrow and secondary pests.

Fallen Scotch pine.
Fallen Scotch pine.

Green Austrian pine in the center of photo has fallen over.Yellowish-red tree on left is heavily infested and dying. Remaining trees have significant damage and will eventually die.
Green Austrian pine in the center of photo has fallen over.Yellowish-red tree on left is heavily infested and dying. Remaining trees have significant damage and will eventually die.

One way to diagnosis if your trees have root collar weevil is to dig around at the base of the tree – the root collar area. With pine root collar weevil, the soil and bark near the root collar of infested trees becomes black and soaked with pitch.

Homeowners can take advantage of the sensitivity of adult weevils to temperature and light when developing an integrated management program for pine root collar weevil. Basal prune young trees – by removing the lowest one to two whorls of branches – to allow more light to reach the root collar. Where ever practical, rake away litter from the base of the tree. If trees are living but show early signs of larval feeding in the root collar, or if pine root collar weevil populations are in nearby pine stands, scrape away the surface soil as well as the litter. Usually, pruning, raking or soil scraping will only need to be done once in a rotation. Avoid mulching trees in areas where pine root collar weevil is a common problem.

For more information, read MSU Extension bulletin E-2560, Life History and Control of Pine Root Collar Weevil in Christmas Tree Fields.

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