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

 

For Immediate Release

 

Contact: Robert Waggener, Editor

Phone: (307) 766-3571

E-mail: robertw@uwyo.edu

 

Date: July 17, 2006

Landscaping Tips

Midnight leaf notchers strike again

By Scott Schell, assistant extension entomologist
University of Wyoming Cooperative Extension Service

            Are the edges of the leaves on your favorite shrubs being chewed up? 

            Never see the culprits feeding in the daylight? 

            You may have to go out at midnight with a flashlight to catch the small, 1/3-inch-long beetles called black vine weevils (Otiorhynchus sulcatus) in the act. 

            The above-ground activity of the flightless beetles is evidenced by the small, square-shaped feeding notches in the leaf margins. They are very different from the larger, round- and oval-shaped holes left by the day-flying leaf-cutter bees. 

            If you think the leaf-feeding damage is bad, seeing the root damage caused by the grubs of this species would be a shock. 

            Older, well-established plants can withstand the damage, but new, container-grown plants can be severely stunted or killed by the root feeding. 

            The black vine weevil and two related species, the strawberry root (Otiorhynchus ovatus) and rough strawberry root (Otiorhynchus rugostriatus) weevils, are believed to have spread around the northern United States by transportation in plant containers since their introduction from Europe. 

            These pests are well established in most Wyoming areas, and control will need to be an annual task, especially for new plantings. If isolated in the country, you may be able to eliminate them for years at a time with just one, thorough control program.

            To successfully manage any insect pest, first understand its biology and ecology. 

            The black vine weevil is known to cause damage to more than 100 species of plants in our region. The adult weevils usually emerge from pupal cases in the soil in mid-June. This event can be monitored with a paper cup buried flush with the soil surface under a host plant to act as an early-warning pitfall trap. 

            After two weeks of feeding, the beetles start to lay eggs around the base of host plants.  The eggs hatch in late July producing root-feeding larvae (grubs). The weevils have only one generation per year.

            If the grubs in the root zone are successfully controlled in late summer, there will be little root damage next spring and few adults to attack the leaves and lay eggs next summer.   

            Three commonly sold insecticides with the active ingredients acephate, bifenthrin and permethrin are labeled for foliar application to control the adult beetles. The label of any insecticide should be followed closely.

            Insecticide products that would be safe to use on lilacs or yews may not be labeled for use on strawberries or raspberries.

            Products that contain the organically derived insecticide spinosad are also labeled for leaf-feeding beetles on a wide variety of plants and would be worth a try for organic gardeners. 

            After the eggs hatch in mid-summer, the small larvae start feeding until the soil gets too cold.

            Two options are available to control the root-feeding grubs. 

            Soil drenches of insecticides containing the active ingredient imidacloprid provide good, season-long protection for ornamental shrubs. 

            Also effective are applications of commercially available insect parasitic nematodes from either the Heterorhabditis or Steinernema genera. The nematode products can be safely used around berry bushes. If the directions are closely followed and the soil conditions are warm and moist, you will get rid of the mysterious leaf notches for a long time.

            Persons with questions may contact their local University of Wyoming Cooperative Extension Service office.  Information is at http://uwadmnweb.uwyo.edu/UWCES/County_Areas.asp.  

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