Nicosulfuron and Primisulfuron Selectivity in Corn (Zea mays) and Two Annual Grass Weeds

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Abstract
Research was conducted to elucidate mechanism(s) of nicosulfuron and primisulfuron selectivity in corn, woolly cupgrass, and shattercane. Corn absorbed less than one half the nicosulfuron and primisulfuron that woolly cupgrass and shattercane absorbed. Acetolactate synthase (ALS) isolated from three species responded similarly to nicosulfuron and primisulfuron. Values for 50% (I50) inhibition of ALS for nicosulfuron were 36.9, 37.2 and 29.5 nM for corn, woolly cupgrass and shattercane, respectively. Primisulfuron I50values were 13.8, 11.5 and 10.0 nM for corn, woolly cupgrass and shattercane, respectively. Shattercane's I50was different from corn's but not from that of woolly cupgrass. Corn rapidly metabolized nicosulfuron and primisulfuron, with a half-life of less than 4 h. Shattercane metabolized the herbicides more slowly, with a half-life greater than 72 h for nicosulfuron and 36 h for primisulfuron. Nicosulfuron and primisulfuron half-lives were greater than 72 h and less than 4 h, respectively, in woolly cupgrass. Therefore, selectivity with nicosulfuron and primisulfuron is likely based on metabolism to nonphytotoxic compounds. Corn tolerance to nicosulfuron and primisulfuron was also attributed to reduced herbicide penetration and translocation below the treated leaf.

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