Pine trees damaged by mid-July hail storms in portions of northern Washington County should be left alone until next year unless more than half of their needles have turned brown, according to the Minnesota DNR.
Following heavy winds and hail on July 12, many red pines in a 14-mile swath from the Hugo-area to Scandia and Marine on Saint Croix have been showing signs of Diplodia, a fungal disease that commonly affects red pines after hail, causing their needles to turn red. Most trees will survive if there is adequate precipitation.
“Dipodia doesn’t usually kill mature red pine so they should be left to recover,” said Jeff Wilder, DNR forester. “However, trees with more than 50 percent crown death have a hard time recovering and may die.”
Landowners may wish to remove severely injured trees later this fall or winter. Otherwise, they should wait until next year to see how well the trees recover. Red pine branches and logs greater than 4 inches in diameter that are cut down in the spring and summer should be chipped within six weeks of cutting to remove bark beetles habitat. Bark beetles thrive in the freshly-cut wood and prefer to attack stressed trees. These beetle populations increase when wood is left behind and can then spread to surrounding trees.
Most other tree species in the hail storm area have minor damage and no serious problems are expected.
Visit the DNR’s Pine Bark Beetle webpage at go.usa.gov/xRnuB for information on pine bark beetles. Visit the DNR’s Diploda-Related Problems of Pine webpage at go.usa.gov/xRUf8 for information on Diplodia.