Cooperative Extension Service Communications and Technology Department 3354 1000 E. University Ave. Laramie, WY 82071 (307) 766-2540 • fax (307) 766-3998 • www.uwyo.edu

 

Contact: Robert Waggener, Editor

Phone: (307) 766-3571

E-mail: robertw@uwyo.edu

 

Date: May 22, 2006

Landscaping Tips

Crawlers are coming to Wyoming

By Scott Schell

Assistant extension entomologist

UW College of Agriculture

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 over-winter, 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.

Dormant oils can be used before bud break to smother over-wintering 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.

New 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 the 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.

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

Local CES horticultural educators or Master Gardeners can also help or refer you to someone who can answer your questions. The telephone numbers and addresses of CES offices can be found at http://uwadmnweb.uwyo.edu/UWCES/County_Areas.asp

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