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.

Experiments were conducted at three locations in Louisiana from 1992 to 1994 to evaluate broadleaf weed control with sulfentrazone. Sulfentrazone at 0.42 kg ai/ha applied PPI or PRE provided at least 93% control of entireleaf morningglory in all years at all locations, which was greater than control with metribuzin PRE. Prickly sida control with sulfentrazone ranged from 83 to 94%, which was equal to or greater than control with metribuzin. Hemp sesbania and sicklepod control with sulfentrazone was unacceptable (≤75%) regardless of application method and generally was lower than control with metribuzin. Greater than 90% control of smellmelon and hophornbeam copperleaf was observed with all treatments. Minor but transient soybean injury was noted at one location in one year. Soybean yields following sulfentrazone PRE at St. Joseph were greater than yields with metribuzin as a result of the general increase in broadleaf weed control.

Greenhouse studies were conducted to investigate the effects of adjuvant and rainfall on bentazon spray retention, efficacy, and foliar washoff in hemp sesbania, sicklepod, smooth pigweed, and velvetleaf. Bentazon was applied at 0.28 to 2.24 kg ai/ha with Agri-Dex, a crop oil concentrate (COC) or Kinetic, an organiosilicone-nonionic surfactant blend (OSB) when weeds were at the three- to five-leaf stage. Plants were subjected to 2.5 cm simulated rainfall for 20 min at 1 and 24 h after application of bentazon. Shoot fresh weight reduction assessed 2 wk after treatment was similar with either adjuvant on velvetleaf and smooth pigweed. OSB enhanced bentazon efficacy in hemp sesbania and sicklepod as compared to COC. Rainfall at 1 h after application generally reduced bentazon activity in all weeds. OSB maintained bentazon activity in hemp sesbania when subjected to rainfall at 1 h after application as compared to COC. Overall, bentazon spray retention on plants was 9 to 550% higher with OSB as compared to COC among the species at 1 h after application. Amount of bentazon residue washed off from the foliage by rainfall within a weed species was relatively similar for both adjuvants except in smooth pigweed and ranged from 39 to 98% among the four weed species at 1 h after application. OSB exhibited specificity for certain weed species and the potential to minimize bentazon spray reaching the soil by increasing deposition.

Cloransulam postemergence (POST), diclosulam preemergence (PRE), and flumetsulam preplant incorporated (PPI) and POST were evaluated in six trials at two locations for control of sicklepod and pitted morningglory in soybean. Sicklepod control with cloransulam plus flumetsulam POST was equivalent to chlorimuron POST in seven of eight comparisons both 3 and 6 wk after treatment. Sicklepod control with cloransulam POST was equivalent to chlorimuron in only three of eight comparisons 3 wk after treatment, but late-season control was equivalent in five of six comparisons. Pitted morningglory control with cloransulam alone or in tank-mixture with flumetsulam POST was equivalent to chlorimuron in all comparisons. Control of sicklepod and pitted morningglory was greater in most comparisons when a POST application followed flumetsulam plus trifluralin PPI compared to only trifluralin PPI. In a total PRE stale seedbed system, where all treatments were tank-mixed with pendimethalin plus glyphosate, sicklepod control with all rates of flumetsulam and 26 or 35 g ai/ha diclosulam was equivalent to the standard treatment of imazaquin or metribuzin plus chlorimuron. None of the total PRE programs controlled sicklepod as well as when glyphosate was applied sequentially POST. Pitted morningglory was controlled 83 to 93% with 26 or 35 g/ha diclosulam, equivalent to imazaquin, metribuzin plus chlorimuron, or sequential glyphosate applications 8 wk after the PRE application. Increasing flumetsulam rate increased pitted morningglory control early season, but flumetsulam was not as effective as the other herbicides.

Field experiments were conducted from 1993 to 1995 to compare weed control by the isopropylamine salt of glyphosate at 0.21, 0.42, 0.63, and 0.84 kg ae/ha applied at three stages of weed growth. Weed control by glyphosate applied at these rates alone or with ammonium sulfate at 2.8 kg/ha was also evaluated. In other experiments, potential interactions between glyphosate and acifluorfen, chlorimuron, and 2,4-DB were evaluated. Velvetleaf, prickly sida, sicklepod, pitted morningglory, entireleaf morningglory, palmleaf morningglory, and hemp sesbania were controlled more easily when weeds had one to three leaves compared with control when weeds had four or more leaves. Glyphosate controlled redroot pigweed, velvetleaf, prickly sida, sicklepod, and barnyardgrass more effectively than pitted morningglory, entireleaf morningglory, palmleaf morningglory, or hemp sesbania. Increasing the rate of glyphosate increased control, especially when glyphosate was applied to larger weeds. Greater variation in control was noted for pitted morningglory, palmleaf morningglory, prickly sida, and velvetleaf than for redroot pigweed, sicklepod, entireleaf morningglory, or hemp sesbania. Ammonium sulfate increased prickly sida and entireleaf morningglory control but did not influence sicklepod, hemp sesbania, or barnyardgrass control. Acifluorfen applied 3 d before glyphosate or in a mixture with glyphosate reduced barnyardgrass control compared with glyphosate applied alone. Chlorimuron did not reduce efficacy. Mixtures of glyphosate and 2,4-DB controlled sicklepod, entireleaf morningglory, and barnyardgrass similar to glyphosate alone.

In 12 trials in Louisiana, sicklepod, entireleaf morningglory, pitted morningglory, and hemp sesbania control 4 wk after planting was greater with trifluralin applied PPI followed by chlorimuron plus metribuzin applied PRE than with trifluralin plus flumetsulam applied PPI. Sicklepod control with these herbicides was similar 6 wk after application. No differences in soybean yield were noted. Chlorimuron applied POST following trifluralin applied PPI and metribuzin applied PRE or trifluralin plus flumetsulam applied PPI improved weed control and soybean yield compared with soil-applied herbicides alone. Excellent barnyardgrass control was obtained with all herbicide programs.

Field studies were conducted from 1991 through 1993 to compare Weed control, peanut tolerance, yield, and net return from imazethapyr applied alone or in combination with paraquat. Sicklepod and Florida beggarweed were controlled with paraquat early POST followed by a POST application of either paraquat with 2,4-DB or paraquat with 2,4-DB and bentazon. Imazethapyr-based early POST treatments offered no improvement. An early POST application of paraquat with bentazon or imazethapyr was required for maximum control of bristly starbur. Imazethapyr applied alone early POST, with no further treatment, provided optimum yellow nutsedge control. Maximum yield and net return were associated with any paraquat-containing early POST-applied treatment followed by one of the tank mixed POST options.

Field experiments were conducted at Jay and Marianna, FL in 1988 and 1989 to determine the effects of sicklepod, Florida beggarweed, and common cocklebur density on chlorothalonil deposition to peanut foliage, peanut foliar disease incidence, and peanut yield. At a density of four weed plants per 8 m of row, Florida beggarweed and sicklepod reduced chlorothalonil deposition on peanut foliage by 20%, while common cocklebur reduced fungicide deposition by 34%. At the same density, incidence of the foliar diseases early leaf spot and late leaf spot increased 10% with Florida beggarweed, 14% with sicklepod, and 20% with common cocklebur compared with weed-free peanut. The predicted peanut yield loss from a weed density of four plants per 8 m was 16 to 19% for Florida beggarweed, 23 to 25% for sicklepod, and 31 to 39% for common cocklebur. Weed biomass increased with increasing weed density.

The effects of ammonium sulfate and pelargonic acid on weed control with glufosinate and glyphosate and safety to glufosinate-resistant and glyphosate-resistant soybean were investigated in the greenhouse and field. Annual and perennial weeds varied in their sensitivity to the herbicides. Based on fresh weight reduction 10 d after treatment (DAT), common milkweed was more tolerant to glufosinate, and horsenettle was more tolerant to glyphosate. Giant foxtail was highly sensitive to both herbicides. The activity of glufosinate on common milkweed and of glyphosate on horsenettle was enhanced with the addition of 5% (wt/v) ammonium sulfate. The addition of pelargonic acid at 3% (v/v) did not enhance the activity of glufosinate or glyphosate on any weed, and it antagonized common lambsquarters and giant foxtail control with glufosinate and with glyphosate. Glyphosate was more effective than glufosinate in suppressing the regrowth of the perennial weeds horsenettle and common milkweed, but addition of ammonium sulfate and pelargonic acid was not beneficial with either herbicide. Under field conditions, the addition of ammonium sulfate or pelargonic acid to glufosinate or glyphosate did not improve efficacy on annual weeds. The addition of pelargonic acid improved yellow nutsedge control with glufosinate, but only at 6 DAT. Glufosinate and glyphosate applied alone or in combination with ammonium sulfate were safe to transgenic soybeans resistant to the respective herbicide. The addition of pelargonic acid to glufosinate or glyphosate in the greenhouse caused a rate-dependent reduction in soybean fresh weight. In the field, slight soybean injury with the addition of pelargonic acid was evident 6 DAT, but not 23 DAT. Addition of ammonium sulfate can increase the efficacy of glufosinate and glyphosate on perennial weeds without negatively affecting soybean yield.

Field studies were conducted in Alabama in 1998 and 1999 to evaluate fomesafen preemergence (PRE) in glyphosate-resistant cotton. Fomesafen (0.3 and 0.4 kg ai/ha), fluometuron (1.4 kg ai/ha), and pyrithiobac (0.05 kg ai/ha) were applied alone or in tank mixtures. Glyphosate (0.4 kg ae/ha) was applied postemergence over-the-top (POT) and postemergence directed (PD). Regardless of PRE treatment, POT followed by (fb) PD applications of glyphosate were necessary for greater than 82% sicklepod control at midseason. In the absence of glyphosate, fomesafen, and fomesafen-containing tank mixtures controlled common cocklebur and Ipomoea species 77 and 72%, respectively, 14 d after PD application. However, two applications of glyphosate were needed for >94% season-long control of common cocklebur and Ipomoea species because of continued germination throughout the growing season. Postemergence applications of glyphosate added a 1,000 kg/ha seed cotton yield increase to all PRE treatments at both locations. Common cocklebur, Ipomoea species, and sicklepod control was not significantly increased by the addition of fomesafen PRE tank mixtures fb glyphosate postemergence as compared with glyphosate postemergence only.

Field studies were conducted over 2 yr to evaluate weed control, yield, and net returns of glyphosate-resistant soybean using total postemergence (5 wk) (POST) herbicide systems with glyphosate–isopropylamine (Ipa) or glyphosate–trimethylsulfonium (Tms) alone, tank mixed with fomesafen, or in sequential treatments with bentazon, fomesafen, Ipa, or Tms. Soybean early-season injury ranged from 0 to 28% across the test. Although Ipa did not injure soybean, glyphosate–Tms early postemergence (3 wk) (EPOST) injured soybean from 7 to 17% depending on the rate. Glyphosate–Tms mixed with fomesafen EPOST injured soybean from 20 to 28%. Red morningglory control by Ipa and Tms at 0.8 kg ae/ha was no more than 88%. Sequential applications of Tms or Ipa controlled red morningglory 78% or less. Fomesafen improved red morningglory control by Ipa and Tms. Bentazon did not affect the control of red morningglory by these herbicides. Sicklepod, smooth pigweed, and large crabgrass control was 81, 93, and 79%, respectively, or greater for all herbicide treatments. By midseason, narrow-row soybeans had canopied, and competition from weeds was minimal. Overall, the net returns were reflective of soybean yield, and maximum net returns were recorded for treatments with reduced herbicide inputs. Conversely, sequential application of herbicides as EPOST followed by POST treatments resulted in lower net returns because of increased herbicide and application costs.