Field experiments were conducted in 2001 and 2002 to evaluate the efficacy of herbicides on protoporphyrinogen oxidase (protox, EC 188.8.131.52) inhibitor–resistant common waterhemp in corn and soybean. All corn herbicides tested gave greater than 90% common waterhemp control by 8 wk after postemergence herbicide treatment (WAPT). In soybean, common waterhemp control was less than 40% by 8 WAPT with postemergence protox-inhibiting herbicides lactofen and acifluorfen. However, preemergence protox-inhibiting herbicides sulfentrazone and flumioxazin gave greater than 85% common waterhemp control in both years. The greatest common waterhemp control in soybean was with glyphosate alone, alachlor metribuzin, alachlor followed by (fb) glyphosate, and S-metolachlor metribuzin fb glyphosate.
Nomenclature: Acifluorfen; alachlor; flumioxazin; glyphosate; lactofen; S-metolachlor; metribuzin; sulfentrazone; common waterhemp, Amaranthus rudis Sauer #3 AMATA; corn, Zea mays L. # ZEAMX ‘RRX740RR’; soybean, Glycine max (L.) Merr. ‘Asgrow 3701’.
Additional index words: Acetochlor, ALS-resistance, atrazine, bromoxynil, carfentrazone, clomazone, clopyralid, dicamba, diflufenzopyr, dimethenamid-P, flumetsulam, glufosinate, halosulfuron-methyl, imazamox, imazaquin, imazethapyr, isoxaflutole, mesotrione, pendimethalin, primisulfuron-methyl, prosulfuron, protox-resistance, thifensulfuron-methyl.
Abbreviations: ALS, acetolactate synthase; proto, protoporphyrin IX; protogen, protoporphyrinogen IX; protox, protoporphyrinogen oxidase; WAPT, weeks after postemergence herbicide treatment.