Ask SAM: Biological control of field bindweed makes headway

This column is provided by Larimer County Extension's Small Acreage Management (SAM) Program to assist rural residents.

Dear SAM,

Are there alternatives to herbicides for bindweed control?

Harry G.

Dear Harry,

If field bindweed has been bugging you, now you can bug it back.

Field bindweed is very difficult to control. Herbicides often do nothing more than burn off leaves and stems without affecting roots. Herbicide applications are sometimes inappropriate, and the plant's widespread distribution guarantees that most bindweed will escape treatment.

Fortunately, a microscopic mite has been introduced as a biological control agent against field bindweed. The bindweed mite, Aceria malherbae, feeds only on field bindweed and some closely related plants, and causes damages only to bindweed. Mite feeding produces folded leaves and distorted growth called galls. Heavily galled plants do not produce vines, flowers or seeds. Affected plants eventually expend the stored nutrient supplies in the root systems and die. It may take several years for bindweed mites to kill a plant, but the bindweed will have reduced water consumption, seed production and competition with surrounding vegetation in the time between infestation and death.

Bindweed mites were introduced into western Colorado in the late 1990s by the Colorado Department of Agriculture Insectary in Palisade. CSU Cooperative Extension received a grant from the Environmental Protection Agency in 2003 to assist in distribution of bindweed mites with the goal of reducing the amount of herbicide used in the environment.

Bindweed mites work best on dryland sites. Plants must be producing new leaves for mites to establish well. The mites do not perform as well under irrigation. The chance of success in controlling bindweed with mites alone declines as the intensity of irrigation increases.

Mites move to new plants with wind, movement of infested plant material or incidental transport by animals and other insects. Mite movement can be enhanced by regular mowing of the bindweed. This physically moves the mites around and stimulates the bindweed to grow. Without any management, mites move slowly. With active management, mites can infest a relatively large area in a year or two.

Bindweed mite damage can be seen within a few weeks if they are released early in the season. Damage from late season releases may not appear until the next growing season. The success rate for establishment on nonirrigated sites is more than 75 percent at the sites we have visited.

Mites will be available from CSU Cooperative Extension on Tuesday, May 24, at the East Exhibition Hall at The Ranch. An educational program will begin at 6:30 p.m. and mites will be distributed at 7 p.m. Cost for a bag of mites is $20. Only 200 bags will be available. Please call 498-6000 to reserve your mites.

SAM

Have a question about rural living? Write to Ask SAM, Larimer County Cooperative Extension, P.O. Box 543, Fort Collins, CO 80522.