INVESTIGATION OF A CHLORSULFURON-RESISTANT CHICKWEED [STELLARIA-MEDIA(L) VILL] POPULATION

A chickweed population (R) from a farm near Stony Plain, Alberta, was more resistant to chlorsulfuron than a population (S) collected near V egreville, Alberta. In greenhouse experiments, the S population was co ntrolled completely by chlorsulfuron applied at 5 g ha(-1), whereas 22 g ha(-1) was required to reduce dry weight of the R population by 50% . Experiments conducted in a germinator indicated that percentage germ ination of the R population was higher than that of the S population u p to similar to 60 h. Growth analyses in the greenhouse indicated that leaf number, leaf area, shoot dry weight, days to flowering, flower n umber, seed weight and relative yields differed little between the two populations. In field experiments, control of the R population was po or with the sulfonylurea herbicides, chlorsulfuron, metsulfuron methyl , triasulfuron, amidosulfuron and thifensulfuron. Good to excellent co ntrol was obtained with cyanazine/MCPA, linuron, metribuzin, mecoprop, bentazon, metribuzin + MCPA, linuron + MCPA, and mecoprop + bentazon.