Colorado Springs, Colorado
A. With roots that can extend more than 20 feet below the soil and seeds that remain viable for as long as 50 years, field bindweed (Convolvulus arvensis) is a formidable foe in agricultural lands and home landscapes. Fortunately, bio-control programs in Colorado, Texas, and other western states have identified a natural enemy of this invasive plant pest, the bindweed gall mite (Aceria malherbae). Imported from southern Europe, this microscopic mite feeds only on bindweed and closely related wild morning glories, and has proven highly effective at controlling bindweed without the use of herbicides.
“I believe we will always have some bindweed,” says agricultural program specialist Terri Locke, of the Colorado Department of Agriculture Insectary. “But we will always have some mites to keep it in check. We have been working with this project for about 14 years and have found it to be very, very successful.”
While bindweed mites seem to be most effective on dry soils, Locke says she has seen the bio-control do wonders in irrigated fields and lawns. “Our lawn used to be infested with bindweed, and now it is bindweed-free. I have worked with skeptics of bio-control in general, and they have come around to accepting the mites as a good control. I have multiple sites where the mites took so well that the bindweed is gone.”
“The mite is very slow-moving,” explains Jerry Michels, Ph.D., a professor of entomology at the Texas AgriLife Research and Extension Center, Amarillo, Texas A&M University System. “It works best on bindweed infestations that can be mowed 7 to 10 days after the mites are released and then every so often after that. This scatters the mites on clippings. Left to themselves, they move at a rate of about a meter or so per year. With mowing, they can spread several hundred meters in a few days.” Because the mites spread so slowly and are so closely linked to field bindweed, they pose very little risk to other plants in the landscape, even those that are closely related to bindweed.
“From the results of the work we’ve done,” adds Michels, “the bindweed mite is specific to bindweed for reproduction and development. It can survive on a number of Calystegia [false bindweed] species for a short time, but it does not reproduce or, if it does, it causes minimal damage. There has been no evidence at all that they damage Ipomoea species [ornamental morning glories and sweet potatoes].”
Programs to distribute bindweed mites to residents are up and running in a number of states. Check with your state’s department of agriculture or Cooperative Extension service for availability. Establishing the mites in bindweed-infested areas involves putting bindweed that is infested with mites in direct contact with uninfested plants and letting nature take its course. Some patience is needed, too, Locke says. “Bindweed will not disappear from yards overnight. We are hoping to diminish its numbers so it isn’t such a pest for gardeners and farmers. It’s a balance of nature that we’re striving for.”
Locke adds that a moth (Tyta luctuosa) whose larvae feed on bindweed has now been established in Colorado and Oregon and is also being used to successfully control the noxious weed.
Bindweed spreads easily by self-seeding and through a creeping root system that is almost impossible to eliminate by hand weeding.
Originally published in Organic Gardening Magazine, April/May 2012