Tree, turf and ornamental plant update - July 13, 2018

Scout for gypsy moth egg masses, drought stress symptoms, white pine weevil damage to leaders of trees, and rust in conifers.

Leaf scorch is a common symptom of drought stress.
Leaf scorch is a common symptom of drought stress. Photo by Bert Cregg, MSU.

The following is a summary of current plant development and pest activity for landscape professionals, Master Gardeners, nursery and Christmas tree growers.

Symptoms of drought stress are beginning to show up in turf, newly planted Christmas trees and landscape plants. Some of the common symptoms of drought stress include wilting, shedding leaves and needles and leaf scorch. For tips on irrigating plants, see “The do’s and don’ts of irrigating landscape plants” from Michigan State University Extension.

Wilted leaders of many conifers that have been attacked by white pine weevil are visible in Christmas tree fields as well as landscapes. Leaders infested with white pine weevil larvae begin showing symptoms in early July when terminal leaders droop and new growth becomes curled. Eventually, affected shoots will die.

White pine weevil larvae kill the terminal leader and the top two to four years of growth on many varieties of spruce, as well as white and Scots pine trees. These leaders should be pruned out when the first symptoms appear. Cut the terminal leader off 1-2 inches below the area damaged by the weevils. After the dead leader is removed, select a healthy lateral shoot on the uppermost whorl to become the new leader. Often, the tree, especially spruce, will choose one for you.

white pine weevil

White pine weevil in Norway spruce leader. Photo by Jill O’Donnell, MSU Extension.

Gypsy moth numbers were high in several areas in the state this year. Christmas tree and nursery growers will want to take extra precaution and scout fields, field boundaries and container rims for gypsy moth egg masses. If egg masses are found on trees in a block or field, those trees may not be certified for movement to non-infested areas.

gypsy moth eggmass

Gypsy moth egg mass on trunk of spruce tree. Photo by Jill O’Donnell, MSU Extension.

Eastern pine weevil (Pissodes nemorensis) larvae have been found in trees that are weak or stressed from winter injury. Similar damage can be caused by white pine weevil or pales weevil. Like white pine weevil, Eastern pine weevil attacks stressed trees, but the damage is more prevalent on the lower branches and trunk.

There are two types of rusts on Michigan Christmas trees growers should be scouting for: those that cause diseases of stems and twigs and those that cause diseases of needles. Spruce needle rust (Chrysomyxa spp.) and fir needle rust (Uredinopsis spp., Milesina spp.) are beginning to show up on spruce and balsam fir trees. You will find white to orange, blister-like pustules on the underside of the current needles.

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