Glyphosate-resistant kochia confirmed in Neb.
In 2011, work by University of Nebraska, Lincoln (UNL) weed scientists confirmed a population of glyphosate-resistant kochia (Kochia scoparia) in Keith County, Neb. This population has resulted in numerous weed control failures in the past two years. Based on other field reports in 2011, it is believed that there may be many populations in western Nebraska that are resistant to glyphosate.
This development was not unexpected. Glyphosate-resistant kochia was first reported in the U.S. in Kansas in 2009 and since then has developed into a serious problem in western Kansas. The vast amount of seed produced by each kochia plant and its ability to disseminate over large distances makes it a major threat to crop production in the High Plains region of the U.S.
UNL Research Confirming Resistance
Greenhouse studies were conducted in 2011 to determine if a population from Keith County was glyphosate-resistant, and if so, to what level. Dose response studies were conducted with 10 treatments of a 5 lb ae/gal glyphosate formulation. Treatments were 0 to 12x the recommended rate. A known glyphosate-susceptible population from Kansas was used with suspected susceptible and resistant populations from Nebraska. Plants were sprayed when the average height reached three inches.
Results suggest a 10 to 15 fold level of resistance in the Keith County population relative to the Nebraska susceptible population. These results also indicate that labeled glyphosate use rates are not adequate for desired control. To achieve acceptable control of glyphosate-resistant kochia use an effective burndown program that does not rely solely on glyphosate and effective tank mixtures. Because glyphosate is relatively cheap, producers may be tempted to manage problem populations with higher rates of glyphosate. Our results indicate this is not a viable management option and will result in 1) greater selection pressure for higher levels of resistance in resistant populations and 2) a greater percentage of resistant plants within the total population.
Reports of herbicide resistance in kochia is not a new phenomenon in the U.S. Kochia populations resistant to triazine (1976), ALS (1987), and growth regulator (1997) herbicides have been reported on the International Survey of Herbicide Resistant Weeds website (source: http://www.weedscience.org/).
Kochia is an early germinating summer annual broadleaf weed species. It can be found in crop fields throughout the Midwest. It is especially common in corn, soybean, wheat, pasture, and right-of-way areas in central and western Nebraska. Kochia is capable of self- or cross-pollination, making it likely that glyphosate resistance could spread via gene flow. It also can spread via the plant’s unique seed dispersal mechanism. After the plant has matured, it will break off at the ground and roll in the direction of a slope or wind. As it rolls, seed is dislodged and deposited in new areas, disseminating the genetics from a single plant over great distances.