Herbicide Susceptibility and Biological Fitness of Triazine-Resistant and Susceptible Common Lambsquarters (Chenopodium album)

Abstract

Biological fitness and negative cross-resistance to other herbicides may be an important factor in managing triazine-resistant common lambsquarters. Greenhouse experiments examined the sensitivity of a resistant and a susceptible biotype to foliarly-applied bentazon, bromoxynil, dicamba, pyridate, and thifensulfuron. The noncompetitive vigor of triazine-resistant and susceptible common lambsquarters also was compared by growing plants in individual containers and harvesting them periodically throughout their vegetative period and at reproductive maturity. In the herbicide susceptibility study, 11 kg ai ha−1atrazine had no effect on the growth of the resistant biotype, while it reduced susceptible common lambsquarters’ biomass by up to 68%. Estimated I50values indicated the resistant biotype exhibited between 36 and 79% greater susceptibility to bentazon, bromoxynil, dicamba, and pyridate than did the susceptible one, while both responded similarly to thifensulfuron. In growth studies, the susceptible biotype achieved greater height, leaf area, and plant dry weight than the resistant population for the majority of harvest dates; however, values equalized between biotypes as the plants reached maturity. These experiments suggest that alternative management programs that exploit reduced fitness and increased herbicide susceptibility in triazine-resistant common lambsquarters could be developed. However, further studies are needed to determine whether these results have application for the management of triazine-resistant weeds in the field.