Field research was conducted for 2 yr to evaluate response of corn and rice to simulated drift rates of a commercial premix of imazethapyr plus imazapyr [3:1 (w/w)]. Drift rates of the imazethapyr plus imazapyr premix represented 0.8, 1.6, 3.2, 6.3, and 12.5% of the usage rate of 63 g ai/ha (0.5, 1, 2, 4, and 7.9 g/ha, respectively). The imazethapyr plus imazapyr premix applied to six-leaf corn at 7.9 g/ha reduced height 11% compared with the nontreated control 7 days after treatment (DAT) but did not affect corn height 14 and 28 DAT. Corn yield was equivalent regardless of imazethapyr plus imazapyr rate and ranged from 10,200 to 11,500 kg/ha. At 28 DAT, rice height was reduced 12% when 7.9 g/ha of the imazethapyr plus imazapyr premix was applied early postemergence (EPOST) at two- to three-leaf and 14 and 5% when the imazethapyr plus imazapyr premix at 7.9 and 4 g/ha, respectively, was applied late postemergence (LPOST) at panicle differentiation. Reductions in mature rice height of 11 and 6% were observed when the imazethapyr plus imazapyr premix was applied LPOST at 7.9 and 4 g/ha, respectively, and a 5% reduction was observed for 7.9 g/ha of the imazethapyr plus imazapyr premix applied EPOST. Application of the imazethapyr plus imazapyr premix EPOST at 7.9 g/ha delayed heading in only 1 yr, but heading was delayed both years when applied LPOST. Rice yield was reduced 39 and 16% when the imazethapyr plus imazapyr premix was applied LPOST at 7.9 and 4 g/ha, respectively, compared with a 9% yield reduction for 7.9 g/ha applied EPOST.

The effect of nicosulfuron application timing on wild-proso millet (Panicum miliaceum) control and sweet corn (Zea mays) yield was evaluated in the field during 1991, 1992, and 1993. Sweet corn yields were equal to hand weeded controls when nicosulfuron was applied to wild-proso millet shorter than 9 cm, but the best (> 95%) wild-proso millet control occurred when nicosulfuron was applied to wild-proso millet plants between 11 and 19 cm tall. However, nicosulfuron controlled wild-proso millet 90 to 95%, 13 wk after planting, when nicosulfuron was applied to plants 8 to 10 cm tall. Nicosulfuron applications made to wild-proso millet plants less than 8 cm were made early in the season and failed to control subsequent wild-proso millet flushes. Additionally, nicosulfuron failed to control completely wild-proso millet plants larger than 20 cm. Consequently, nicosulfuron applied to wild-proso millet plants shorter than 8 cm or taller than 20 cm resulted in a rapid decline in wild-proso millet control 13 wk after planting. Nicosulfuron applied following 6.7 kg ai/ha EPTC plus 2.2 kg ai/ha cyanazine PPI in 1991, could be applied to wild-proso millet 25 cm tall without subsequent losses in wild-proso millet control or sweet corn yield. Wild-proso millet control was 93% and sweet corn yields were equal to hand-weeded controls when nicosulfuron was applied to wild-proso millet 4 cm tall and followed by one cultivation 14 d after application.

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A study was conducted in 1999 to evaluate weed control and imidazolinone-tolerant (IMI-tolerant) rice response to 140 g ai/ha imazethapyr at different application timings and to flood depths of 5, 10, and 20 cm at the Rice Research Station near Crowley, LA, and at the Northeast Research Station near St. Joseph, LA. Barnyardgrass control, rice injury, and rice yield were not influenced by flood depth; therefore, data were averaged over flood depths. Season-long barnyardgrass control was greater than 80% at both locations with imazethapyr applied preplant incorporated (PPI), early postemergence (EPOST), and mid-postemergence (MPOST). IMI-tolerant rice injury at 7 d after late postemergence (LPOST) treatment (DAT) was less than 5% for all imazethapyr treatments at Crowley and 1 to 8% for PPI, preemergence (PRE), delayed preemergence (DPRE), and EPOST timings at St. Joseph. However, IMI-tolerant rice injury was 5% or less at 42 DAT for all treatments at Crowley and St. Joseph. IMI-tolerant rice yield at Crowley was 2,780 to 3,000 kg/ha following applications of imazethapyr at PPI, PRE, DPRE, and EPOST, and these yields were higher than the yields of the MPOST and LPOST treatments. At St. Joseph, IMI-tolerant rice yields were equal for imazethapyr applied PPI, DPRE, and EPOST treatments compared with Crowley.

Sweet corn tolerance to nicosulfuron as affected by interactions between nicosulfuron applied postemergence (POST), sweet corn hybrid, and rootworm insecticide applied at planting was determined in 1992 and 1993 field experiments. Sweet corn vigor was reduced as nicosulfuron rate increased from 35 to 140 g ai/ha. Sweet corn vigor was reduced 4% more by nicosulfuron with oil emulsifier mixture than nicosulfuron with non-ionic surfactant one week after treatment (WAT). Adjuvant selection did not influence nicosulfuron injury to sweet corn 2 WAT. Nicosulfuron applied postemergence directed (PDIR) caused less sweet corn injury than nicosulfuron applied broadcast POST. ‘Jubilee’ sweet corn was more sensitive to nicosulfuron and insecticide treatments than ‘Excellency’ or ‘Green Giant 40.’ Nicosulfuron reduced sweet corn vigor twice as much when terbufos was applied at planting compared to no insecticide at planting. Neither chlorpyrifos or chlorethoxyfos at planting increased sweet corn injury due to nicosulfuron compared to no insecticide. Excellency and Green Giant 40 yields were not reduced by any treatment. Yields were reduced only when nicosulfuron was applied to Jubilee treated with terbufos. Jubilee yield reduction from nicosulfuron and terbufos was prevented by applying nicosulfuron PDIR.