Wild Buckwheat
by Charles Geddes
Word alert: oc·re·a
Noun BOTANY
- a dry sheath around a stem formed by the cohesion of two or more stipules, characteristic of the dock family.
Description and Identification
Also known as black-bindweed, climbing bindweed, corn bindweed, or Polygonum convolvulus.
In western Canada, wild buckwheat has been the third most abundant mid-season weed species in spring wheat for decades. Like wild oat, this weed is found throughout the Canadian Prairies. Wild buckwheat is an annual species that reproduces by seed. This vine-like weed climbs crop plants in search of light and tangles the crop canopy together, causing problems at harvest. A wild buckwheat-infested crop often takes longer to harvest because the vine tends to wrap around the combine header, which can damage mechanical components if the weed is not removed. Among the Prairie Provinces, wild buckwheat is found in 48% of spring wheat fields, where it occurs at an average density of about 4 plants per square metre.
Wild buckwheat seedlings can be identified most easily by a slender stem often red in colour, slender linear cotyledons, and simple alternate heart-shaped leaves. The stem has long smooth internodes and an ocrea at each node (not shown). Initially, the seedling grows erect, but later grows prostrate in a twining or creeping manner. The vines can grow between 5 cm and 200 cm in length and wrap around neighbouring plants. The seed head includes small greenish clustered perfect flowers in the leaf axils or at the tips of branches or short racemes. Wild buckwheat flowers indeterminately throughout the growing season and produces hard, black, triangular-shaped seeds.
Photo: CM Geddes
Biology and Habitat
Wild buckwheat grows in both cultivated and non-cultivated habitats and populations of wild buckwheat can persist for several years or even decades. In the soil seed bank, wild buckwheat seed can persist for 6 to 10 years. The hard, relatively impermeable seed coat requires damage or scarification to allow for germination, which can result in unpredictable emergence patterns. The seed can germinate and emerge from up to 20 cm below the soil surface; however, most seedlings emerge from less than 5 cm depth. In western Canada, wild buckwheat begins to germinate in April and continues to germinate throughout the growing season. Wild buckwheat can produce up to 12,000 seeds per plant and result in about 12% yield loss in cereal crops at densities of about 5 plants per square metre.
Herbicide Resistance
Most wild buckwheat populations in the Canadian Prairies have avoided selection for herbicide resistance. The first cases of wild buckwheat resistant to the ALS-inhibitor (group 2) herbicides florasulam, thifensulfuron, and tribenuron in western Canada were confirmed in Alberta in 2007. To the best of our knowledge, wild buckwheat has not evolved resistance to any other herbicide modes of action. However, wild buckwheat is naturally tolerant to several herbicides including MCPA, 2,4-D, or even glyphosate and lower label rates.
Management
Many products remain effective for control of wild buckwheat, including: bromoxynil, clopyralid, dicamba, glufosinate and sulfonylurea herbicides. Bromoxynil tends to be the most efficacious and recommended choice for control of wild buckwheat in cereal crops, and application at earlier growth stages results in improved management. This contact herbicide burns the leaves of the plant, resulting in eventual starvation. Tolerance of wild buckwheat to systemic herbicides is dependent on the stage of the plant at the time of application. If an applicator uses systemic herbicides like glyphosate or the ALS-inhibitors it is best to apply prior to the 4-leaf stage of wild buckwheat. Beyond this stage, herbicide efficacy may be reduced.
Photo: CM Geddes
Effective non-chemical tools for management of wild buckwheat include shallow tillage to promote germination, followed by subsequent tillage or harrow passes and late-seeding of summer annual crops. Crop rotation to perennial forage production, including forage harvest or grazing by livestock at multiple times throughout the growing season also can help manage wild buckwheat populations.
For more information, visit: https://farmingsmarter.com/weed-wisdom-oct-2017/