Kochia (Kochia scoparia) is an early-emerging summer annual species commonly found in the western United States. |
It is a herbaceous dicot and member of the Chenopodiaceae family (the same botanical family as common lambsquarters). Kochia was introduced into North America from Europe as an ornamental because of its red color in late summer and fall (hence, kochia's other common name, "fireweed").
In recent years, kochia has become more common in many areas of Illinois. It is commonly found along railroad rights-of-way and frequently spreads from these areas into neighboring cornfields and soybean fields. Kochia possesses several characteristics that make it well suited as a weed in agronomic production systems.
Kochia Morphology and Biology
Kochia leaves are alternate with simple blades that are highly pubescent.
Stems are erect, highly branched, often grooved on older plants,
and vary in color from green to red, often with both colors present on an individual plant. Kochia has an imperfect flower that allows cross-pollination to occur,
which has important implications for the spread of certain herbicide-resistance traits. Seed production is moderate to high, depending on environmental and competitive conditions. Seed dispersal occurs via a "tumbleweed" mechanism by which the mature stem detaches from its base and is subsequently blown about by wind. Kochia seed is short lived in the soil, but possesses a high initial germination rate. Results from one published study indicate that up to 93% of kochia seeds produced the previous season germinate within 1 year. Seed germination is generally greater at shallow soil depths and progressively decreases with increasing soil depth, making no-till systems a good environment for kochia. Seedling emergence can occur very early in the spring, so kochia is typically one of the first summer annual weed species to emerge. Studies have reported kochia emergence when average minimum daily soil temperature ranged from 37 to 46°F.
Kochia biotypes with resistance to triazine and acetolactate-synthase (ALS) inhibiting herbicides have been well documented. Triazine-resistant kochia first appeared in 1976 along railroads in Idaho and Iowa, where triazine herbicides had been used continuously for total vegetation control. In 1987, the first kochia biotype resistant to ALS-inhibiting herbicides was discovered. Since these initial reports, herbicide resistance in kochia has spread rapidly. Most Illinois kochia samples have demonstrated resistance to triazine or ALS-inhibiting herbicides. We have documented the existence of an Illinois kochia biotype resistant to both triazine and ALS-inhibiting herbicides. Widespread herbicide resistance in the Illinois kochia population should be considered when formulating a chemical-control program for corn or soybeans.
One of the most effective kochia control options is tillage. Since kochia germinates very early in the season, a tillage operation prior to corn or soybean planting can sometimes eliminate most kochia for the remainder of the season. If tillage is not an option, a burndown herbicide should be selected that has good activity on kochia. Some effective burndown herbicides include Gramoxone Extra, glyphosate, and dicamba. Glyphosate rates of 0.375 lb. a.e. (13 fluid ounces of Roundup UltraMax) or less may not provide good burndown control, especially during cool temperature conditions. 2,4-D is generally less effective than dicamba. Triazine and several ALS-inhibiting herbicides have very good efficacy on kochia, but with widespread resistance to these herbicides in Illinois kochia populations, herbicides with these modes/sites of action should not be relied on exclusively for kochia control. Command (clomazone) is an effective soil-applied soybean herbicide, while glyphosate can be used for postemergence control in glyphosate-resistant soybean varieties. Other postemergence soybean herbicides that can suppress or control kochia include Cobra (lactofen) or Flexstar (fomesafen). Balance and Epic are effective soil-applied corn herbicides, while postemergence kochia control in corn can be obtained with Tough, Buctril, or products containing dicamba.--Aaron Hager and Christy Sprague