Selectivity of nicosulfuron and primisulfuron in three annual grasses

Abstract

Research was conducted to elucidate niechanism(s) of nicosulfuron and primisulfuron selectivity in com, woolly cupgrass and shattercane. Com absorbed less than one half the nicosulfiiron and primisulfuron that woolly cupgrass and shattercane absorbed. Acetolactate synthase (ALS) isolated from three species responded similarly to nicosulfuron and primisulfuron. Values for 50% (Ijo) inhibition of ALS for nicosulfuron were 36.9, 37.2 and 29.5 nM for com, woolly cupgrass and shattercane, respectively. Primisulfuron Ijo values were 13.8,11.5 and 10.0 nM for com, woolly cupgrass and shattercane, respectively. The shattercane I50 was statistically different than the com but not the woolly cupgrass IJQ. Com rapidly metabolized both nicosulfijron and primisulfuron, with a half-life of less than 4 h. Shattercane metabolized the herbicides more slowly, with a half-life of greater than 72 h for nicosulfiiron and 36 h for primisulfuron. Nicosulfuron and primisulfuron half-lives were greater than 72 h and less than 4 h in woolly cupgrass. Therefore, selectivity with *Grad. Res. Asst. and Prof, respectively. Agronomy Dept., Iowa State Univ., Ames, IA,50011-1010.