Response of Johnsongrass (Sorghum halepense) and Imidazolinone-Resistant Corn (Zea mays) to AC 263,222

Field studies were conducted in 1992 and 1993 to evaluate AC 263,222 applied postemergence (POST) alone and as a mixture with atrazine or bentazon for weed control in imidazolinone-resistant corn. Nicosulfuron alone and nicosulfuron plus atrazine were also evaluated. Herbicide treatments were applied following surface-banded applications of two insecticides, carbofuran or terbufos at planting. Crop sensitivity to POST herbicides, corn yield, and weed control was not affected by insecticide treatments. AC 263,222 at 36 and 72 g ai/ha controlled rhizomatous johnsongrass 88 and 99%, respectively, which was equivalent to nicosulfuron applied alone or with atrazine. AC 263,222 at 72 g/ha controlled large crabgrass 99% and redroot pigweed 100%, and this level of control exceeded that obtained with nicosulfuron alone. AC 263,222 at 72 g/ha controlled sicklepod and morningglory species 99 and 98%, respectively. Nicosulfuron alone or with atrazine controlled these two species less than AC 263,222 at 72 g/ha. Addition of bentazon or atrazine to AC 263,222 did not improve control of any species compared with the higher rate of AC 263,222 at 72 g/ha applied alone. Corn yield increased over the untreated control when POST herbicide(s) were applied, but there were no differences in yield among herbicide treatments.

Red Rice (Oryza sativa) andEchinochloaspp. Control in Texas Gulf Coast Soybean (Glycine max)

Field studies were conducted from 1992 to 1994 to evaluate herbicides applied preplant incorporated (PPI), preemergence (PRE), and postemergence (POST) for red rice andEchinochloaspp. control in soybean. Metolachlor PPI at 3.4 kg ai/ha controlled red rice late season 90 to 92%. Alachlor at 4.5 kg ai/ha and SAN 582H at 2.2 or 3.4 kg ai/ha, PPI or PRE, metolachlor plus imazaquin at 2.8 + 0.14 kg ai/ha PRE, and quizalofop-P POST at 0.07 kg ai/ha provided 83 to 95% red rice control in at least 2 of 3 yr. The addition of imazaquin to metolachlor or pendimethalin did not improve red rice control. Early-seasonEchinochloaspp. control with trifluralin, pendimethalin, and pendimethalin + imazaquin applied PPI; metolachlor, SAN 582H at 2.2 or 3.4 kg/ha, and metolachlor + imazaquin applied PPI or PRE; alachlor, AC 263,222 + imazaquin, and AC 263,222 + imazethapyr applied PRE; and sethoxydim and quizalofop-P applied POST was 90 to 100% in at least 2 of 3 yr. However,Echinochloaspp. control decreased for all treatments later in the season. Pendimethalin applied PPI at 2.2 kg ai/ha or in mixture with imazaquin at 1.7 + 0.14 kg ai/ha injured soybean 14 to 34% in 2 yr. Trifluralin PPI, SAN 582H at 2.2 or 3.4 kg/ha PPI or PRE, imazaquin PPI, metolachlor + imazaquin PPI or PRE, and AC 263,222 + imazethapyr injured soybean 12 to 41% in at least 1 of 3 yr.

Leafy Spurge (Euphorbia esula) Response to AC 263,222

Leafy spurge is an exotic perennial weed that infests more than 1 million ha in North America and reduces rangeland carrying capacity. Experiments were initiated on range sites in Nebraska and North Dakota in 1994 and 1995 to determine the response of leafy spurge and other vegetation to AC 263,222. Herbicide treatments evaluated included AC 263,222 at 0 to 280 g ai/ha, picloram at 560 g ai/ha plus 2,4-D at 1,120 g ae/ha, and quinclorac at 1,120 g ai/ha. In Nebraska, a single application of AC 263,222 in the fall at 140 g/ha provided ≥ 90% leafy spurge control 11 to 12 mo after treatment. At Jamestown, ND, leafy spurge control increased to almost 90% and stem density declined to two shoots/m212 mo after the second consecutive fall application of AC 263,222 at 140 g/ha. At Hankinson, ND, leafy spurge control was ≤ 50% when AC 263,222 was applied in the fall only, but increased to > 80% when AC 263,222 was applied in the fall and again at 70 or 140 g/ha in the spring. There were no differences in herbage biomass of established cool- and warm-season grasses where AC 263,222 at 140 g/ha, picloram plus 2,4-D, quinclorac, or no herbicide was applied in the fall. In contrast, application of AC 263,222 in the fall and again in the spring usually reduced cool-season grass biomass.

AC 263,222 absorption and fate in leafy spurge (Euphorbia esula)

Absorption, translocation, and metabolism of AC 263,222 by leafy spurge were studied over 8 d. Based on the amount of herbicide applied and recovered from the leaf surfaces, 40% of applied AC 263,222 was absorbed by leafy spurge 2 d after treatment (DAT), with no further absorption observed by 8 DAT. Eight DAT, 19% of applied [14C]-AC 263,222 had translocated to below-ground plant parts while 4% was exuded from the roots into the sand media. AC 263,222 was not metabolized 2 DAT in the crown, root, and root buds, but 42% was metabolized in the treated leaves. Only 17% of recovered [14C] was AC 263,222 in treated leaves 8 DAT (83% metabolized), while AC 263,222 accounted for 70% of recovered [14C] in the root and root buds. HPLC analysis indicated that the balance of [14C] was associated with a single, polar metabolite. Total recovery of [14C] was 88% at 8 DAT.

Herbicide Programs for Red Rice (Oryza sativa) Control in Soybean (Glycine max)

A study was conducted in 1994 and 1995 at two Mississippi locations to evaluate preplant incorporated (PPI) and preemergence (PRE) applications of alachlor, clomazone, SAN 582, metolachlor, pendimethalin, and trifluralin, and postemergence (POST) applications of AC 263,222 and imazethapyr alone or followed by clethodim late postemergence (LPOST) for red rice control in soybean. Applications of 110 g ai/ha clethodim increased red rice control when following any earlier herbicide application at one location that harbored a high natural infestation. In 1 yr at one location, red rice seedhead suppression from PPI and PRE herbicide applications alone was greater than 95% due to high activity from herbicides and drought conditions during red rice seedhead development. Early postemergence (EPOST) applications of 30 g ae/ha AC 263,222 suppressed at least 95% of red rice seedheads, regardless of year, location, or clethodim LPOST application. At one location, any treatment where 110 g/ha clethodim followed an earlier herbicide application suppressed red rice seedheads at least 95%. Compared to the nontreated control, only AC 263,222 injured soybean (30%) and reduced soybean yield (200 kg/ha).

Influence of Herbicides and Timing of Application on Broadleaf Weed Control in Peanut (Arachis hypogaea)

Field studies were conducted from 1992 through 1994 to evaluate application timing of seven postemergence (POST) broadleaf herbicides alone and in mixtures for control of eclipta and pitted morningglory. Imazethapyr and 2,4-DB did not control eclipta while AC 263,222 applied early postemergence (EPOST) at 0.07 kg/ha provided greater than 90% control in 2 of 3 yr. EPOST applications of bentazon, acifluorfen + bentazon, and pyridate controlled eclipta at least 92% all 3 yr. Lactofen applied EPOST at 0.28 kg/ha provided similar levels of eclipta control in 2 of 3 yr. Imazethapyr controlled pitted morningglory > 70% when applied EPOST. AC 263,222 controlled pitted morningglory a minimum of 83% when applied EPOST at 0.04 or 0.07 kg/ha. Pitted morningglory control was at least 85% with 2,4-DB applied alone or in a mixture with AC 263,222, acifluorfen, imazethapyr, lactofen, or pyridate. Effective weed control increased peanut yields up to 98% over the untreated check.

Control of Palmer Amaranth (Amaranthus palmeri) in Peanut (Arachis hypogaea) with Postemergence Herbicides

Seven postemergence (POST) herbicides were evaluated alone and in various mixtures for Palmer amaranth control in peanut from 1992 through 1994. AC 263,222 at rates as low as 0.04 kg/ha controlled ≥ 95% Palmer amaranth. Imazethapyr at rates of 0.05 to 0.07 kg/ha controlled ≥ 90% Palmer amaranth in 2 of 3 yr. Acifluorfen alone or in combination with bentazon or 2,4-DB and lactofen alone controlled > 90% Palmer amaranth in 2 of 3 yr. Bentazon or pyridate failed to provide adequate control (≤ 60%), while 2,4-DB provided good control (80%) in only 1 of 3 yr.

Influence of Postemergence Herbicides on Tropical Soda Apple (Solanum viarum) and Bahiagrass (Paspalum notation)

Greenhouse and field experiments were conducted to evaluate herbicidal efficacy on tropical soda apple and bahiagrass. Acifluorfen, clopyralid, dicamba, fluroxypyr, picloram, and triclopyr were the most effective postemergence herbicides, providing > 90% control of tropical soda apple plants with no injury to bahiagrass 145 days after treatment (DAT). Glyphosate and imazapyr resulted in effective (> 90%) control of both seedling and mature tropical soda apple plants. However, these herbicides caused severe (> 90%) damage to bahiagrass. Control of tropical soda apple with 2,4-D, AC-263,222, diuron, fomesafen, lactofen, MSMA, sulfometuron, and triasulfuron was unacceptable (> 90%).

Nutsedge (Cyperusspp.) Control in Peanut (Arachis hypogaea) with AC 263,222 and Imazethapyr

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.