Experiments were conducted from 1988 through 1991 to evaluate the effectiveness of imazethapyr alone and in combination with metolachlor for control of yellow and purple nutsedge. Imazethapyr alone at 0.07 kg ha–1controlled yellow nutsedge irregularly while the addition of metolachlor greatly improved control. Metolachlor preplant incorporated (PPI) followed by imazethapyr at ground-crack (GC) or postemergence (POST) controlled 72 to 96% of yellow nutsedge, whereas a tank-mix of metolachlor plus imazethapyr PPI controlled 85 to 96%. The addition of metolachlor to imazethapyr did not result in any improvement in control of purple nutsedge. Metolachlor plus imazethapyr PPI controlled ≥ 85% of purple nutsedge PPI, whereas imazethapyr POST controlled ≥ 94%.

Experiments were conducted from 1991 through 1993 to evaluate AC 263,222 and imazethapyr for yellow and purple nutsedge control in peanut. AC 263,222 at 0.05 to 0.07 kg/ha controlled purple nutsedge (88 to 99% late season) whether applied preplant incorporated (PPI), preemergence (PRE), early postemergence (EPOST) at peanut emergence, or postemergence (POST). Yellow nutsedge control with AC 263,222 was inconsistent at the 0.04 kg/ha rate; however, the 0.05 and 0.07 rate gave 88% early season yellow nutsedge control, but late season control was variable. Yellow nutsedge control with soil-applied treatments of AC 263,222 and imazethapyr were similar but AC 263,222 provided better postemergence control than did imazethapyr. Purple nutsedge control was similar for both herbicides across all application methods.

Field studies were conducted in 1991 and 1992 to evaluate the response of soybean and the subsequent rice crop to AC 263,222 applied alone and in tank mixtures with imazethapyr or imazaquin. In 1991, 18, 36, and 70 g ai/ha of AC 263,222 visibly stunted soybean 9, 19, and 35%, respectively. Adding imazethapyr at 36 g/ha or imazaquin at 70 g/ha to AC 263,222 in a tank mixture did not increase soybean response compared to AC 263,222 alone. Soybean yield was not reduced by any treatment. In 1992, 14 g/ha of AC 263,222 alone or in tank mixtures damaged soybean 38% or greater. In one study, rice was injured the year following application of AC 263,222 alone and in tank mixtures. Rice yield was reduced by 70 g/ha of AC 263,222 alone and by 36 g/ha of AC 263,222 when tank mixed with 36 g/ha of imazethapyr.

Field studies were conducted in 1997 and 1998 to evaluate the efficacy of imidazolinone weed management systems and crop tolerance of imidazolinone-tolerant (IT) corn to imazapic. Imazapic (36 and 72 g/ha) was evaluated when applied PRE; early postemergence (EPOST), when corn was at the two- to three-leaf stage; and late postemergence (LPOST), when corn was at the six- to eight-leaf stage. Imazapyr + imazethapyr EPOST and metolachlor + atrazine followed by (fb) primisulfuron LPOST were evaluated as commercial standards. Imazapic at 36 g/ha EPOST controlled johnsongrass, Texas panicum, smellmelon, and ivyleaf and entireleaf morningglory at least 93% when adequate rainfall occurred. Devil's claw was controlled at least 85% with imazapic EPOST or LPOST at either rate. Imazapic at 36 g/ha EPOST and LPOST controlled eclipta 88 and 91%, respectively. Yellow nutsedge was controlled >91% with imazapic LPOST, which was superior to imazapic applied EPOST. Broadleaf signalgrass was controlled 94% with imazapic at 72 g/ha LPOST, which was significantly higher than other herbicide treatments. Imazapic at 36 and 72 g/ha applied PRE under moisture stress resulted in reduced weed control; but when adequate rainfall occurred, weed control was generally similar to that of EPOST and LPOST applications. Imazapic crop response at 72, 105, 140, and 211 g/ha applied at EPOST and LPOST was evaluated in two IT corn hybrids. Crop response varied with soil and environmental conditions and application timings. Imazapic at 72, 105, and 140 g/ha EPOST resulted in crop injury 33 to 55% at 6 wk after planting (WAP) in a coarse soil; however, crop injury decreased to <20% at 12 WAP. Low crop injury (<9%) was observed at 12 WAP in a clay soil. Imazapic applied LPOST resulted in lower crop injury than EPOST application. Corn plant height and yield were not affected by any imazapic treatment.

Field studies were conducted to document the response of itchgrass [Rottboellia exaltata(L.) L.f. ♯3ROOEX] in soybean [Glycine max(L.) Merr. ‘Forrest’] to selected herbicides and postplanting cultivation. Early cultivation stimulated emergence of itchgrass seedlings; however, when plots were cultivated two or three times, itchgrass was effectively removed from the tilled area. Cultivation had no effect on the density, height, standing biomass, or seed production of itchgrass plants in the soybean row but did increase soybean yield. In response to a density reduction of 90%, the average weight, number of tillers and branches, and seed production of single itchgrass plants increased by a factor of 2.9, 3.1, 2.3 and 2.6, respectively, in trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-treated plots. Individual plants did not increase growth following density reduction by a postemergence application of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Itchgrass plants competing for the entire season in plots treated with trifluralin reduced soybean yield approximately 21 g per weed, while itchgrass recovering from diclofop treatment and competing the remainder of the season reduced yield approximately 5 g per weed.