Harmful insects cutting a swath through Wisconsin

After years of causing damage in southeastern Wisconsin, viburnum leaf beetle (VLB) larvae were spotted at a nursery in the central part of the state in Wausau, in early June. This pest is native to Europe, and has been found in Wisconsin, since 2014.

It severely defoliates ornamental and native viburnums, while the recent detection occurred on arrowwood viburnum, which, unlike the more resistant doublefile, Koreanspice and Judd viburnum, is highly preferred by this pest.

The beetle infestations can be controlled with horticultural oil to smother eggs, and contact insecticide to kill larvae (also known as caterpillars) and adults.

Encouraging natural predators like ladybugs and selecting resistant shrubs for landscaping, also help manage this invasive insect.

In additon the hot, dry weather in Wisconsin, in June, resulted in a variety of scales during nursery inspections, including: cottony maple scale on autumn fantasy, autumn blaze and sienna glen maple; European elm scale on princeton elm; Fletcher scale on multiple varieties of arborvitae and yews; juniper scale on arborvitae and blue rug creeping juniper; Lecanium scales on oak, hackberry and apple trees; magnolia scale on magnolia; poplar scale on quaking aspen; and rose scale on prairie rose and swamp rose.

In many cases throughout the state, inspectors found eggs and crawlers, the mobile stage of scale insects, hatching out and on the move. Crawlers are tiny and can be hard to see, without a hand lens or other magnifier. Once properly identified, crawlers are the ideal stage for targeting effective treatments, since adult scales are covered by protective waxy coverings resembling shells.

Left unchecked, scale insects reduce plant health and vigor by feeding on the plant sap causing the foliage to discolor, twig dieback and can ultimately cause plant death.