Field bindweed is one of the most difficult weeds in western Montana. It is a persistent perennial vine in the morning-glory family, with arrowhead-shaped leaves and white, funnel-shaped flowers.
Bindweed thrives in disturbed soils where there is little competition from other plants. It invades most aggressively in areas that are repeatedly disturbed and exposed to lots of sunlight. It does not do as well in shade or in very wet, soggy soils. Bindweed competes best in moderate to low moisture areas.
The secret of bindweed's success is its prodigious root system. It produces an extensive system of roots and rhizomes (underground stems). One plant can fill an area 20 feet in diameter and 30 feet deep.
Field bindweed forms rhizomes in the spring and begins to spread as soon as daytime temperatures reach 60 degrees F and night temperatures stay above 35 degrees F.
Field bindweed spreads mostly by seed, and seeds can remain viable in the soil for more than 20 years. Unfortunately, bindweed also spreads by root and rhizome pieces. It can proliferate if tilled lightly and broken into small parts.
Fortunately, field bindweed is not quite invincible; it does have some weaknesses. Roots can be killed if exposed to freezing and drying conditions. Freezing temperatures kill bindweed stems back to the ground. Leaves and stems do not grow well in shade.
Alfalfa, cereal grains, and cover crops reduce bindweed growth and seed production by shading. When bindweed stems start to grow again in early May, root carbohydrate reserves are at their lowest and the weed is most vulnerable to repeated tillage.
These weaknesses can be used in a field bindweed management plan. The plan requires time (several years) and multiple tools in order to:
• reduce seed in the soil,
• prevent seedling growth, and
• deplete food reserves in the root system.
Frequent tilling reduces root food reserves and depletes the soil seed bank. But frequency is the key. Tillage every 14 days will weaken the weed. One tilling may actually encourage bindweed. Start tilling when temperatures are still dropping well below freezing at night to expose roots to cold and dry.
After several months of tillage, plant a thick, fast-growing cover crop to shade bindweed and reduce its regrowth. A mixture of oats and peas was effective in one study. Alfalfa or clovers are other good options.
Researchers suggest that light reduction must be 50 percent or greater for three years to control a serious field bindweed infestation.
Don't try cover crops that allow light to reach the soil surface. For example, field bindweed can invade a buckwheat cover crop by climbing up buckwheat stems to reach the light. In general, cover crops that grow vigorously during late fall and early spring seem to compete best with bindweed.
Black paper or plastic mulches are somewhat effective in controlling small patches of field bindweed. Complete coverage of the bindweed is important.
Sheep and cattle will graze field bindweed, but in one study, even continuous, intensive grazing over several years only suppressed field bindweed. It was able to recover when grazing was stopped.
For more information on field bindweed management, call your local county extension agent.
Helen Atthowe is a Missoula County extension horticulturist. She can be reached by calling (406) 258-4200.