Garden calendar: For the week of January 12

Garden calendar: For the week of January 12

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Pests: They’re ba-ack! Last year, right around this time, the Wisconsin Department of Agriculture, Trade and Consumer Protection reported finding the invasive insect Elongate Hemlock Scale, or EHS on holiday greens. Once again, this season they have been reported on holiday garlands, wreaths, Christmas trees (fir, specifically) and other greens.

EHS feeds on more than 40 conifer species, with hemlock, spruces and firs being among the most susceptible. EHS removes nutrients as it feeds on the underside of conifer needles, weakening the plants. EHS is a threat to Wisconsin Christmas tree farms, native hemlock and balsam fir forests, and ornamental conifers in yards and parks. Unfortunately, cold winter weather does not kill it.

Elongate hemlock scale is native to Asia and has been introduced into Michigan and many Eastern states. Look for light brown and/or white oval, slightly raised bumps on the underside of needles, possibly accompanied by a sticky feel to the needles that indicates feeding is going on (this is a hard symptom to be conclusive about since evergreen resin is sticky as well).

EHS has several growth stages. After hatching from eggs, tiny mobile “crawlers” feed on the underside of needles. Eventually, they build a hard shell around themselves, creating the “scale” that is visible. EHS becomes immobile at that point and for the rest of its life span stays stuck to the underside of the evergreen needle. New crawlers are produced underneath the “mother” scales.

Crawlers start new infestations; wind and birds may also disperse scales to new trees. EHS is very hard to control with insecticides, due to the overlapping generations with crawlers present all year long, and because adult scales are protected under their hard, waxy shells.

If you purchased your Christmas tree, wreaths, garlands, or other decorations from a local Christmas tree farm or the greens were grown elsewhere in Wisconsin, no special precautions are needed, because EHS is not established in the state. You can dispose of these greens as usual at the end of the holiday season.

However, if you purchased your tree or greens from a big box store, grocery store, or similar vendor, or if you are not sure of the origins of these materials, please check these materials for signs of EHS.

The Wisconsin DATCP advises that infested or suspect materials preferably be burned (you will need to check with the DNR regarding burning restrictions in your area), or you can bag and discard the materials in your regular garbage. Do not compost any infested greens or those you are not sure about.

For more information about EHS, visit the UW Insect Diagnostic Lab at https://insectlab.russell.wisc.edu/ .

Lisa Johnson, Dane County UW-Extension horticulture educator

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