News Release
May 29, 2007

Landscaping Tips
The crawlers are coming to Wyoming

By Scott Schell, Assistant Entomologist UW CES, (307) 766-2508

Spring brings the appearance of the immature stage of many scale insect species called crawlers.

Scale insects belong to the order Homoptera, which includes many other important plant pests such as aphids, whiteflies and plant hoppers. Homopteran insects feed by piercing a plant’s tissue with a stiletto-like beak and then sucking the sap or cell contents.

What separates scale insects from other Homopterans is that an adult female becomes attached to a plant for life, lacks functional wings and legs and secretes a scale-like covering that protects her and her eggs from most predators and insecticides. Depending on the species, the secretion can either be hard or soft. The shape and construction of the scale can be used to identify the species.

Many species are found in Wyoming. One of the most widespread is the oystershell scale. It can damage many shrubs and trees and can severely affect lilac bushes. The eggs overwinter, and the tiny, yellowish-white crawlers start hatching in early June.

Another common species is the pine needle scale. It feeds on many conifers but can be especially bad on spruce trees, causing discoloration, premature needle shed and branch dieback. The peak hatch of light purpled-colored pine needle scale crawlers usually coincides with the peak bloom of the lilac bushes.

The crawlers are the easiest life stage of the scales to control. Proper tree care, which includes pruning and destruction of scale-infested branches before crawlers emerge, is a good management tool. Branches can be taken to compost facilities or landfills, if allowed, or they can be cut up and composted at home. The chipping process and high heat from composting should ensure destruction of the scale.

Gardeners who don’t want to prune out infested branches can physically remove the scales with mildly abrasive plastic scrub pads sold for washing dishes. This can be done by gently scrubbing the scales from the affected areas.

Dormant oils can be used before bud break to smother overwintering scales. These are light oils derived from petroleum or plant sources that must be applied when a deciduous tree or shrub is dormant.

Horticultural oils work well on immature hard scales, but care must be taken to avoid toxic reactions on the new leaves. These oils are special formulations that can be applied after the leaves are present.

Crawlers can be killed with pyrethroid or carbaryl insecticide applications labeled for this use. Correct timing is critical because the sprays are ineffective if applied after the crawlers attach to the plant and secrete the protective scale.

Neonicotinoid-type systemic insecticides, containing the active ingredients imidacloprid or dinotefuran, applied as a soil drench can provide year-long control of the soft scales and suppression of hard scales with less impact on beneficial and non-target insects. Neonicotinoids are based on the chemistry of the potent alkaloid nicotine found in plants like tobacco. A soil drench is a way of applying insecticide by mixing the correct amount of product in a bucket of water and then slowly pouring it around the base of the plant.

The optimum timing for application for these insecticides is early fall, but they will work gradually if applied in the spring or summer. The products are applied once and can provide season-long control as they are incorporated into the plant tissue.

The label of any insecticide product chosen must be followed carefully and exactly. Local lawn and garden stores commonly carry products labeled for this pest, and Colorado State University’s home use insecticide database Web site lists most commonly available products. The address is http://homeusepesticide.org/.

For more information on scales, see the University of Wyoming Cooperative Extension Service (UW CES) bulletin Scales and Mealybugs at www.uwyo.edu/ces/PUBS/B1050-1.pdf. The bulletin is also available from UW CES offices in each county.

Local UW CES horticultural educators and Master Gardeners can also help or refer you to someone who can answer your questions. Contact information is at http://ces.uwyo.edu/Counties.asp.

Contact: Robert Waggener, Editor
Phone: (307) 766-3571
E-mail: robertw@uwyo.edu

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