Tree, turf and ornamental plant update – June 22, 2018

Spittlebugs, woolly larch adelgid and imported rose sawflies are active. Galls on tree leaves and spruce bud scale are visible.

June 22, 2018 - Authors: Howard Russell, Rebecca Finneran, Jill O'Donnell, David Smitley, and Irene Donne

Imported rose sawfly larva, Arge ochropus (Argidae).
Imported rose sawfly larva, Arge ochropus (Argidae). Photo by Nolie Schneider, Ottawa, Ontario.

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

Landscapes

Spittlebugs (Aphrophora parallela) and woolly larch adelgid (Adelges laricis) can be found on tamarack (American larch) trees. Spittlebugs feed on tree sap and produce a frothy, white spittle mass on shoots. Woolly larch adelgid feed on larch needles. With both of these pests, damage is minimal and does not require any treatment unless the tree appears to be coated with snow.

Many homeowners are noticing strange-looking bumps on their tree leaves. Spindle gall, bladder galls and other galls are now showing up on the leaves of maples and linden trees. These galls are formed as a plant response to feeding by mites and insects. Galls usually do not affect the tree’s health and once the galls are formed, it is too late for treatment.

Nursery Christmas trees

Spruce bud scale (Physokermes piceae) is being found in higher numbers on Norway and Colorado blue spruce. Spruce bud scale may often go unnoticed since their size and color can cause them to be mistaken for buds. They are round, reddish-brown and often clustered in groups of three to eight at the base of new shoots. Lower branches are more often attacked than higher branches. Severe infestations can produce lots of honeydew that will allow sooty mold to grow.

MSU Diagnostic Services

We are getting more reports of imported rose sawfly damaging roses in southeast Michigan. This European species was first found in North America in Ontario, Canada. It first appeared in Michigan in 2007 in Monroe County, but was not officially confirmed until 2016. It feeds on wild and cultivated species of rose.

Unlike most species of sawflies we see in Michigan, the imported rose sawfly has two generations each year. The life cycle is not well-documented in North America, so the following our best guess based on specimens received and client reports. The winter is probably passed in the pupal stage in the soil. Adults emerge in spring, mate and the females lay 16 to 18 eggs at a time on the upper, succulent rose stems. First generation larvae are present in late May through June. First generation adults emerge in July. Second generation larvae appear in late summer and fall from August through October.

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