Response of two catchweed bedstraw (Galium aparine) populations to post-emergence herbicides in winter wheat

Abstract

Catchweed bedstraw causes severe problems in winter wheat and other winter sown crops. Field experiments were conducted from 2005 to 2008 in wheat fields in Samsun, Turkey, to determine: (1) the response of catchweed bedstraw to chlorsulfuron, tribenuron-methyl plus thifensulfuronmethyl, dicamba plus triasulfuron and mesosulfuron-methyl plus iodosulfuron-methyl-sodium; and (2) possible resistance or tolerance to these herbicides. The herbicides were applied at the 2-4, 4-6, and 6-8 true leaf stages of biomass, there were large differences among the upper limits of the dose-response curves, and consequently, the actual response curve, an asymmetric sigmoid curve, was fitted to data to obtain 50% and 90% effective dose, ED50 and ED90, values. None of the herbicides reduced catchweed bedstraw biomass or populations satisfactorily when applied at the recommended field rate. Twice the recommended field rate was required to achieve acceptable reduction in biomass. Overall, inadequate control of this weed cannot be solely attributed to either acetolactate synthase (ALS) resistance or improper application methods. It is likely due to a slow and progressive development of ALS-tolerant populations after many years of consecutive use.