CORVALLIS. Ore. – The white, trumpet-shaped flowers called bindweed that seem to bloom everywhere can be one of the most frustrating weeds for home gardeners.
This invasive perennial makes itself at home by sinking roots as much as nine feet into the soil and can stay on as an unwanted guest for up to 20 years. Known to weed scientists as "field bindweed" (Latin name: Convolvulus arvensis), it is in the morning glory family and often is confused with wild buckwheat and morning glory, which are summer annual plants.
The field bindweed species is native to Europe and now is distributed worldwide, according to Andy Hulting, an Oregon State University Extension weed specialist.
"It is considered to be one of the most noxious weeds in the world because of its yield-robbing practices in crops such as wheat, potatoes and legumes (beans and peas)," he said.
Spreading by seed and through a deep, extensive horizontal root system, field bindweed seed can persist for many years in typical garden soil. "Although its roots can grow deep, most of the horizontal roots colonize the upper two feet of soil," Hulting said. It tolerates poor soils but seldom grows in wet or waterlogged areas.
"The lack of effective herbicides and soil cultivation in perennial crops, gardens and flower beds results in rapid build up of the species,” Hulting explained.
But strategies to curb this botanical trespasser do exist. Mowing isn't one of them.
Bindweed grows along the ground until it contacts other plants or structures and spreads over anything in its path. Much like pole beans, bindweed's stems rotate in a circular pattern until they attach to a solid structure (fence posts, other plants). The stems wrap around the object as it grows.
If you want to avoid using herbicides to control field bindweed, plan to pull out or plow up all the bindweed for three to five years, Hulting advises. Persistence and dedication are needed to get rid of bindweed; roots left in the soil after cultivation will regenerate in about two weeks.
Be prepared to pull it all up every three weeks. Repetitive cultivation throughout the growing season for at least three years should deplete the root system and provide control.
"Use the deepest cultivation implements available, such as a garden fork," Hulting said, "and be aware that root fragments as small as two inches can generate new shoots. Make sure as much of the root system becomes desiccated as possible."
Glyphosate herbicides (such as Roundup) are an option, as long as you can keep the herbicide spray or drift away from other plants in your yard. These herbicides are absorbed by foliage and move throughout the plant to kill roots and shoots. The best time to control bindweed with glyphosate herbicides is when the plants are flowering.
Repeated applications of herbicide will be necessary to control bindweed. Its root system can be so immense that not enough herbicide can be absorbed with a single application.
"In addition, the texture of field bindweed leaf and stem surfaces forms an effective barrier to absorption and translocation of many herbicides," Hulting explained. "Use repeated applications, but allow the plant to grow and produce flowers before each subsequent application."
Identifying field bindweed can be tricky. Its arrow-shaped leaves grow opposite each other along each stem. When juvenile stems are broken, they exude a milky sap. The flowers are white to pink and trumpet shaped, and produce indeterminately throughout the year.
For more information on how to identify and manage field bindweed, check out publication PNW 580, Field Bindweed Biology and Management, in the OSU Extension Service online catalog.
Also, the Oregon Department of Agriculture has an active and ongoing biocontrol program for large acreage infestations of field bindweed. Visit the ODA biocontrol website.