Field bindweed is a difficult, noxious weed, but it can be managed organically.
It is considered noxious because it can severely reduce yield, and spreads easily. Once established, control requires persistent effort, whether chemicals are used or not.
Field bindweed resembles a morning glory crossed with a wild buckwheat plant. It has small funnel shaped white or pink flowers, a twining stem and arrow shaped leaves.
In behaviour, it has features of wild buckwheat and Canada thistle. The stems climb up taller plants and can bind them together, creating havoc at harvest time.
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A single plant can extend roots three metres horizontally and six metres vertically. It can store food reserves to last two or three years. Seeds can persist for several decades.
Field bindweed is found in all mainland Canadian provinces and through much of the United States. It is increasingly being noticed along the southern border of Saskatchewan.
As with any weed, prevention is the first control method. Cleaning equipment and care in obtaining plant material can prevent introduction of problems.
When field bindweed is first detected, the patch should be isolated to prevent further spread. Pulling isolated plants or hand hoeing may prevent small problems from getting out of control.
If the weed is established near field borders, it may be worth tilling the border to prevent weed spread to neighbouring fields. Preventing seed set is critical because seed can last longer than farmer vigilance.
Seeds germinate in spring and fall. Seedlings are easily controlled by tillage in the first month but once established require more than a single tillage pass.
Farmers must deplete root reserves when controlling established field bindweed plants. Plants are most vulnerable to tillage when they are sending reserves upward to produce flowers and seed.
Tillage repeated every time the plants grow to six inches will further deplete the reserves heading into winter.
According to a study from Kansas, tillage to a depth of four inches was optimal in medium heavy soil.
In South Dakota, tillage every two weeks in June and July and every three weeks in August and September reduced field bindweed by 95 percent in a single year but did not entirely exhaust the root reserves. Such intensive tillage is unlikely to be practical in most situations. Damage from tillage can be reduced if implements such as wide blade sweeps are used.
An alternative to tillage is combining mowing with strong competition. Alfalfa can greatly reduce field bindweed populations because hay cutting depletes the bindweed reserves, and alfalfa regrows more quickly than bindweed, which suppresses it. Three years of alfalfa may be needed to reach an optimal level of control.
Use of winter annual crops such as fall rye and sweet clover provides strong competition in fall and early spring and allows cultivation sooner. Short season green manures allow producers to combine cultivation before and after the crop with increased competition.
Cutting a crop for green feed also allows for a potential cash crop while maximizing cultivation time and reducing the time that the weed has to go to seed.
For best competition, high seeding rates of crops are recommended for both feed and green manures.
A variety of biocontrols are possible. Sheep will graze field bindweed and can keep it in check. Cattle will also eat leaves and stems. Pigs and chickens do even more damage to the plants because they tend to uproot more of them.
The field bindweed leaf and bud gall mite – a long name for a small insect – has been introduced near Medicine Hat to control field bindweed. It causes the plant to produce a gall instead of more stem and can prevent flowering if enough of them attack a plant. The insect prefers new growth so repeated mowing improves biocontrol.
The most effective way to introduce the insect to a new area is to collect galls from an existing colony in the spring and place them into a new bindweed population. The insect colony often lasts only a few years, so repeated introductions may be necessary.
Bindweed control is not quick and easy, but with carefully managed rotations, over time it can be effective.
Frick is the prairie co-ordinator for the Organic Agriculture Centre of Canada located at the University of Saskatchewan. She can be reached at 306-966-4975, at brenda.frick@usask.ca, or www.organicagcentre.ca.
