This World of Weeds article will focus on wild buckwheat (Fallopia convolvulus), sometimes called black bindweed. This annual vining plant is often confused with field bindweed (Convolvulus arvensis) because of their similar leaf shapes and growth habits. However, the two species belong to different weed families, and we’ll examine the key differences between the two.
Ecology
Wild buckwheat is a native of Europe but has become established on all continents except Antarctica. It grows in temperate regions as far north as Alaska and Greenland and as far south as Chile, Argentina, and South Africa. Caches of wild buckwheat seeds have been found at archeological sites dating back to when humans first employed agriculture and permanent settlements more than 4000 years ago. Grain transports likely contributed to the spread of wild buckwheat seeds as contaminants in cereal crops. By 1860, it was established in the United States and in Canada by the 1870’s. Yield losses from wild buckwheat infestations have ranged from 10 to 25% in crops such as wheat, barley, and flax.
Identification
Wild buckwheat is an annual species that reproduces from seeds. Numerous slender stems, up to 6 feet long, are produced near the base of the plant to form spreading vines (Figure 1). Where these vines encounter obstacles (such as other plants), they often encircle and climb upwards toward light (Figure 2). Leaves are typically heart-shaped, alternate, up to 2.5 inches long, with smooth margins. Each leaf is attached to the stem by a long stalk (petiole) and has two broadly spaced, backward-pointing lobes at the base (Figure 3). The presence of an ochrea (membranous sheath) encircling the base of the petiole at the stem is characteristic of plants in the Polygonaceae family, which includes the buckwheat, smartweed, and knotweed species (Figure 4). Flowers are small (< 0.25 inch), green, and inconspicuous. The flowers form small clusters at the leaf nodes and the terminal end of the vines (Figure 5). Seeds are dark brown to black at maturity, three-sided in shape, and often pointed at the top.
Figure 1. A mature wild buckwheat plant showing vines and small flowers. Photo courtesy Michigan State University.
Figure 2. Wild buckwheat climbing a wheat plant. Photo by Sarah Lancaster, K-State Research and Extension.
Figure 3. Field bindweed leaf (left) compared to wild buckwheat leaf (right). Photo courtesy Cornell University.
Figure 4. Leaf of wild buckwheat. Note the long petiole attaching the leaf to the stem and the ochrea surrounding the stem at the petiole base. Photo courtesy Iowa State University.
Figure 5. Wild buckwheat has inconspicuous flowers. Photo by Sarah Lancaster, K-State Research and Extension.
The presence of the ochrea easily distinguishes wild buckwheat from field bindweed. The small, greenish buckwheat flowers are also quite different from bindweed flowers, which are white to pink, showy, and up to one inch in diameter. Bindweed also has two small leafy bracts on the petiole below the flower, which are absent in buckwheat. As an annual species, buckwheat does not produce reproductive rhizomes like bindweed, which is a perennial species. Buckwheat leaves are typically more rounded on the sides (heart-shaped) than bindweed leaves (arrowhead-shaped). (Figure 3)
Management
Historically, wild buckwheat has been most problematic in our continuous cereal crops, such as wheat, and crop rotation has somewhat diminished its presence. Rotation to corn, soybean, sorghum, or another warm-season crop continues to be an excellent strategy for buckwheat management. This allows for the use of control measures not typically used in cereals for buckwheat management. In wheat, cultural practices that increase crop competitiveness will decrease buckwheat competitiveness, such as narrow row spacing, increased seeding rates, and earlier planting to maximize ground cover. Should an herbicide treatment become necessary, preemergence applications of group 2 herbicides such as triasulfuron or chlorsulfuron (Amber, Finesse, others) have shown good activity. Group 2 herbicides also have good to excellent postemergence buckwheat activity. Other postemergence products include the group 6 herbicide bromoxynil and group 4 herbicides dicamba and fluroxypyr. Combinations of these herbicides have shown the best control of wild buckwheat.
Buckwheat has shown some tolerance to the group 9 herbicide glyphosate due to poor absorption and translocation. Currently, no herbicide-resistant wild buckwheat populations are confirmed in the U.S. However, group 2 resistant populations have been identified in Canada, and resistance to atrazine (group 5) has been documented in Europe.
The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.
More information about the control of wild buckwheat can be found at:
Reference
Hume, L. et al. 1983.The biology of Canadian weeds. 60. Polygonum convolvulus L. Can. J. Plant Sci. 63:959-971.
Patrick Geier, Weed Scientist, Garden City
pgeier@ksu.edu
Sarah Lancaster, Extension Weed Management Specialist, Manhattan
slancaster@ksu.edu
Jeremie Kouame, Weed Scientist, Agricultural Research Center – Hays
jkouame@ksu.edu