Impact of Crop Competition on Fitness of Glyphosate-Resistant Kochia (Kochia scoparia L. Schrad).

Kochia (Kochia scoparia L. Schrad) is a member of the Chenopodiaceae family also known as the goosefoot family. Kochia is found throughout Kansas and has become a major weed. Overuse of the herbicides, specifically glyphosate in Roundup Ready crops resulted in the evolution and spread of glyphosate resistance in several weeds including kochia. Glyphosate resistant (GR) kochia has been found across Kansas. However, crop competition in the presence of glyphosate-resistant (GR) or -susceptible (GS) kochia populations is not known. The objective of this study is to determine the impact of crop competition on the growth and fitness of GR and GS kochia populations. Experiments were conducted in competition with oats at two densities (80 and 160 plants/m²) using target neighborhood design with four replications. Data on plant height, stem diameter, number of primary branches, chlorophyll content, and photosynthetic efficiency were collected for kochia plants at 30 and 60 days after transplanting. All data were analyzed by ANOVA in SigmaPlot. The results showed differences in competitive ability between GR and GS kochia plants. These differences are more due to genetic variability in the two kochia populations and may not be related to herbicide resistance mechanism.