Field studies were conducted in 1996 and 1997 at Belleville and Pawnee, IL, to evaluate single and sequential applications of glufosinate on tolerance of glufosinate-resistant corn and annual weed control. Glufosinate caused 0 to 13% corn injury 7 days after treatment (DAT) and 0 to 6% corn injury 28 DAT. Injury was characterized as stunting with glufosinate. Glufosinate at 400 to 1,200 g ai/ha did not reduce final corn height or grain yield. At Pawnee in both years and at Belleville in 1996, a single application of glufosinate at 400 g/ha controlled giant foxtail, velvetleaf, ivyleaf morningglory, and common lambsquarters 85 to 100%. At Belleville in 1997, sequential applications of glufosinate provided greater weed control (87 to 100%) than a single application (0 to 63%) because of weed emergence after application. Weed control with a single application of glufosinate or with nicosulfuron plus bromoxynil was similar at both locations. Height and grain yield of glufosinate-resistant corn were not different from that of glufosinate-susceptible corn (isoline of glufosinate-resistant corn).

Herbicide systems consisting of PRE, early POST, and late POST options arranged factorially were compared for control of sicklepod in narrow-row soybean with modified acetolactate synthase (ALS) (E.C.4.1.3.18). Other weeds present included common cocklebur and mixed infestations of entireleaf, ivyleaf, pitted, and tall morningglories. PRE options were alachlor or alachlor plus metribuzin plus chlorimuron. Early POST options included chlorimuron, chlorimuron plus thifensulfuron, and no herbicide applied 3 wk after planting. Late POST options were chlorimuron and no herbicide applied 5 wk after planting. POST herbicides were more effective than PRE herbicides on all weeds. Chlorimuron and chlorimuron plus thifensulfuron applied early POST were equally effective on these weeds and usually more effective than chlorimuron applied late POST. There was no advantage of two POST applications compared with a single early POST application. Greatest net returns were obtained in systems using only early POST herbicides. There was no economic advantage from using metribuzin plus chlorimuron PRE in systems that included an early POST herbicide.

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.

Barnyardgrass and many broadleaf weeds were severely stunted by POST applications of isoxaben. Most grasses were only moderately affected by isoxaben at rates up to 1 kg/ha. POST activity was enhanced by soil interception, but evident with foliar interception alone. Cell swelling in stems and in interveinal leaf lamina was observed after foliar application. A radiotracer study in redroot pigweed showed that only a small amount (3.3% of applied) of isoxaben entered the leaf following foliar application, and that little (0.08% of applied) isoxaben migrated beyond the point of application. The potential of isoxaben as a POST herbicide may be limited, in part, by poor absorption and translocation.

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.

The penetration, translocation, and metabolism of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} in ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. ♯3 IPOHE], velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), and soybean [Glycine max (L.) Merr.] were studied. An application to plants of 0.3 kg ai/ha mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} 0, 3, 5, or 7 days prior to treatment with 14C-acifluorfen often altered one or more of the physiological processes under study. Pretreatment of ivyleaf morningglory with mefluidide 3, 5, or 7 days prior to application of 14C-acifluorfen increased penetration of 14C and decreased metabolism of acifluorfen, while translocation was unaffected. All mefluidide treatments increased penetration of 14C-acifluorfen into velvetleaf, while the 3-, 5-, and 7-day pretreatments decreased acifluorfen metabolism. Penetration of acifluorfen into common cocklebur was unaffected by pretreatment with mefluidide. However, the 7-day mefluidide pretreatment of common cocklebur increased translocation of 14C into the upper leaves and decreased acifluorfen metabolism. Penetration and translocation of the radiolabel from 14C-acifluorfen in soybean was unaffected by pretreatment with mefluidide. Metabolism of acifluorfen by soybean was decreased by the 0-day mefluidide treatment but was unaffected by the 3-, 5-, or 7-day mefluidide pretreatment.

Thiazopyr at 0.14, 0.28, and 0.42 kg ai/ha and pendimethalin at 1.1 kg ai/ha applied preemergence (PRE) were compared as components in weed management systems for no-till cotton. Mid- and late-season control of mixtures of large crabgrass, goosegrass, and fall panicum by thiazopyr at 0.28 kg/ha was 89 to 97% and 11 to 50%, respectively, compared with 11 to 38% midseason and 0 to 5% late-season control by pendimethalin. Thiazopyr at 0.42 kg/ha and pendimethalin controlled broadleaf signalgrass 44 and 0%, respectively, late in the season. Adding fluometuron PRE at 1.7 kg ai/ha had little to no effect on large crabgrass, goosegrass, and fall panicum control but increased broadleaf signalgrass control 47 to 79 percentage points compared with thiazopyr or pendimethalin alone. Late-season control of annual grasses by thiazopyr or pendimethalin plus fluometuron PRE followed by methazole plus MSMA early postemergence (POST)-directed and cyanazine plus MSMA late POST-directed was at least 95% at two locations and 80% at the third location. Common lambsquarters was controlled 54 and 95% in systems without and with fluometuron PRE, respectively. Acceptable control of ivyleaf, pitted, and tall morningglories at all locations and smooth pigweed at two of three locations was achieved only in systems with POST-directed herbicides. Adding POST-directed herbicides to systems with thiazopyr or pendimethalin plus fluometuron PRE increased cotton yield at two of three locations. Treatments had no effect on fiber quality.

Field experiments were conducted over a 3-yr period at three locations to evaluate lactofen at rates of 110 to 220 g ai ha−1 applied POST in combination with chlorimuron at 9 g ae ha−1 for weed control in soybean. At St. Joseph in 1989 and Baton Rouge in 1990, lactofen at 110, 150, and 170 g ha−1 in combination with chlorimuron controlled prickly sida (3 to 5 cm) and entireleaf and pitted morningglory (5 to 13 cm) comparable with the full rate of lactofen at 220 g ha−1 plus chlorimuron and the standard treatment of acifluorfen at 280 g ae ha−1 plus bentazon at 560 g ae ha−1. Entireleaf morningglory and sicklepod control at Alexandria with lactofen at 110 to 170 g ha−1 plus chlorimuron was comparable with that from the full rate of lactofen plus chlorimuron and better than with acifluorfen plus bentazon. Weed control was reduced when soil moisture was deficient at treatment time or when prickly sida height was more than 5 cm and entireleaf morningglory, pitted morningglory, and sicklepod more than 15 cm. In related studies at St. Joseph, a reduced rate of lactofen (170 g ha−1) in combination with chlorimuron controlled prickly sida 98%, pitted morningglory 93%, and entireleaf morningglory 90% in 1988, which was comparable with the control from the full rate of lactofen plus chlorimuron and with acifluorfen plus bentazon.

Greenhouse and field experiments were conducted to evaluate early postemergence (POST) tank mixtures of SAN 582 with fluazifop-P, imazethapyr, or sethoxydim. In the greenhouse, SAN 582 synergistically improved barnyardgrass, broadleaf signalgrass, and johnsongrass control from imazethapyr and sethoxydim. Half-rates of imazethapyr and sethoxydim tank-mixed with SAN 582 controlled grass weeds as well as full rates of either herbicide applied alone. Grass weed control with imazethapyr increased up to 40% with the addition of SAN 582. In field experiments, SAN 582 increased grass control with imazethapyr to a lesser degree than observed in the greenhouse. In a multispecies study, grass weed control increased up to 15% when SAN 582 was tank-mixed with a reduced rate of imazethapyr, although the full rate of imazethapyr applied POST with or without SAN 582 controlled grass weeds 80% or less. The combination of SAN 582 with sethoxydim was synergistic for barnyardgrass and johnsongrass control in this experiment. When applied POST in soybean, SAN 582 plus fluazifop-P or sethoxydim controlled barnyardgrass throughout the season better than a single POST application of a graminicide.

Methods were developed and evaluated that utilize state of the art weed-sensing technology in row-crop production systems. Spectral differences in green living plants and bare soil allowed ‘real-time’ weed detection, with intermittent spraying of herbicide only where weeds were present. Sensor units were mounted in 0.7-m-wide hooded sprayers providing sensors with an unobstructed view of the area between soybean rows. Single hood and commercial-size eight-row systems were evaluated, and savings in glyphosate spray solution applied using sensors ranged from 63 to 85%, compared to conventional hooded spray systems with continuous application. Weed control by the sensor-controlled spray system was equal to the conventional system. This technology can significantly reduce herbicide usage and decrease production cost without reducing weed control.

Soil-applied imazaquin or chlorimuron plus metribuzin reduced ivyleaf morningglory photosynthetic rate, leaf area, biomass, and seed production per plant compared to the nontreated control. Photosynthetic rate of ivyleaf morningglory was reduced a minimum of 53%, and total leaf area was reduced at least 67% with either herbicide, regardless of ivyleaf morningglory densities. Ivyleaf morningglory biomass and seed production were reduced at least 62% with either herbicide across all ivyleaf morningglory densities. Soybean leaf area, photosynthetic rate, and biomass were not affected by herbicide treatment or ivyleaf morningglory densities of 2, 4, 6, or 8 per m of row.

Research was conducted to determine an effective morningglory control system for cotton grown in central Texas, Prometryn applied PRE or directed-POST applications of methazole or methazole + MSMA did not always adequately control ivyleaf, entireleaf, and seedling sharppod morningglories. However, adequate control of the above species plus pitted morningglory was achieved with a management system that used a dinitroaniline applied PPI or PRE, prometryn applied PRE (0.9 kg ai ha−1), followed by methazole (0.56 kg ha−1) or methazole + MSMA (0.56 + 1.80 kg ha−1) directed POST to cotton 10 to 15 cm high.

Field studies were conducted over 4 yr to evaluate weed control and soybean injury with sulfentrazone applied preplant incorporated or preemergence alone and in combination with imazaquin, metribuzin, or cloransulam. Sulfentrazone at 280 g ai/ha controlled yellow nutsedge, common waterhemp, ivyleaf morningglory, and velvetleaf 92 to 100% 56 days after planting (DAP). At 420 g/ha, sulfentrazone controlled giant foxtail 80 to 94% 21 DAP. Sulfentrazone controlled common ragweed 17 to 93% and common cocklebur 57 to 91%. Giant foxtail, common cocklebur, and common ragweed control with sulfentrazone at lower rates was improved with the addition of metribuzin or cloransulam. Sulfentrazone caused no visual soybean injury and did not reduce yield compared with standard herbicides.

Experiments were conducted in 1991 and 1992 to evaluate the weed control effectiveness from several rates of AC 263,222 applied PPI and PRE (36 and 72 g ai/ha), early POST (EPOST) (18, 36, 54, or 72 g/ha), POST (18, 36, 54, or 72 g/ha), and EPOST followed by (fb) POST (27 fb 27 g/ha or 36 fb 36 g/ha). These treatments were compared to the commercial standard of bentazon at 0.28 kg ai/ha plus paraquat at 0.14 kg ai/ha EPOST fb bentazon at 0.56 kg/ha plus paraquat at 0.14 kg/ha plus 2,4-DB at 0.28 kg ae/ha. Application method had little effect on weed control with AC 263,222. In contrast, application rate affected control. Purple nutsedge, yellow nutsedge, prickly sida, smallflower morningglory, bristly starbur, common cocklebur, and coffee senna were controlled at least 82% with AC 263,222 at 36 g/ha (one-half the maximum registered use rate) regardless of application method. AC 263,222 at 72 g/ha (registered use rate) controlled sicklepod 84 to 93%, Florida beggarweed 65 to 100%, and Ipomoea morningglory species 89 to 99%. A single application of AC 263,222 at 36 g/ha or more controlled all weeds (with the exception of Florida beggarweed) as well or greater than sequential applications of bentazon plus paraquat fb bentazon, paraquat, and 2,4-DB. All rates of AC 263,222 applied POST and all application methods of AC 263,222 at 72 g/ha had better yields than the pendimethalin control.

The effect of adding a spray adjuvant to SAN 582H tank mixtures with fluazifop-P, imazethapyr, and sethoxydim was evaluated. SAN 582H synergistically increased broadleaf signalgrass control with reduced rates of all three postemergence (POST) herbicides when no spray adjuvant was used and when crop oil concentrate was added. For example, broadleaf signalgrass control increased from 50% to 83% when SAN 582H was tank-mixed with 52 g ai/ha sethoxydim and crop oil concentrate. In another experiment, several formulations of SAN 582H, including blank solvent-only formulations (no SAN 582H), were evaluated in combination with a reduced rate of sethoxydim to determine the source of synergism from tank mixtures. The SAN 582H molecule, not the carrier solvents in formulated product, was determined to be the source of synergism. The synergistic properties of SAN 582H were compared to other chloroacetamides. Synergism from acetochlor was similar to SAN 582H when applied POST with a reduced rate of either fluazifop-P, imazethapyr, or sethoxydim for grass control. Metolachlor also synergistically increased the control of grasses with the POST herbicides; however, metolachlor caused considerable phytotoxicity when applied alone and synergistic interactions were detected less frequently. The efficacy of sethoxydim mixed with SAN 582H was evaluated under different soil moisture conditions. Broadleaf signalgrass control increased from 81% to 93% under dry, moisture-stressed conditions when 210 g/ha sethoxydim was tank- mixed with SAN 582H.

Field studies were conducted at five locations in North Carolina and Virginia in 1996 and 1997 to evaluate weed control and peanut (Arachis hypogaea) response to diclosulam that was applied preemergence (PRE) and in systems with commercial standards. All plots received a preplant incorporated (PPI) treatment of ethalfluralin at 840 g ai/ha. Diclosulam controlled common lambsquarters (Chenopodium album L.), eclipta (Eclipta prostrata L.), entireleaf morningglory (Ipomoea hederacea var. integriuscula Gray), ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], pitted morningglory (Ipomoea lacunosa L.), and prickly sida (Sida spinosa L.) as well as and frequently better than the commercial standards of acifluorfen plus bentazon applied postemergence (POST), paraquat plus bentazon early POST followed by (fb) imazapic POST, or imazapic POST. Systems with ethalfluralin PPI plus diclosulam PRE at 26 g ai/ha fb acifluorfen plus bentazon POST controlled a broader spectrum of weeds and yielded greater than systems of ethalfluralin PPI fb imazapic POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PRE at 17, 26, or 35 g/ha.

Experiments conducted in North Carolina and Virginia compared weed control, peanut yield, and net returns with systems using imazethapyr applied at various times and the regional standard treatment of paraquat applied at the ground-cracking stage of peanut (GC) followed by acifluorfen plus bentazon applied POST. Imazethapyr was applied PPI, PRE, GC, or POST at 70 g ae ha−1. Imazethapyr also was applied sequentially PPI plus GC, PPI plus POST, and PRE plus POST at 35 + 35 and 70 + 70 g ha−1. Late-season control of common ragweed and a mixture of entireleaf, ivyleaf, and pitted morningglories by the standard treatment ranged from 85 to 100%. Spurred anoda was controlled 80%, and common lambsquarters and prickly sida were controlled completely. Control of common lambsquarters, prickly sida, and morningglory by imazethapyr applied one or more times was similar to control by the standard. Control by imazethapyr exceeded that by the standard only for spurred anoda. The most effective time for applying imazethapyr varied by species and locations. Imazethapyr was equally effective on common lambsquarters and spurred anoda when applied PPI, PRE, or GC. Prickly sida and morningglory were controlled best when imazethapyr was applied PPI or PRE and GC, respectively. Common ragweed was controlled poorly with single applications of imazethapyr. Applying imazethapyr sequentially improved consistency of control across the range of species. In most cases, imazethapyr applied sequentially at 35 + 35 g ha−1 controlled all weeds as well as or better than when applied once at 70 g ha−1. Overall, imazethapyr at the registered rate of 70 g ha−1 was most effective when applied PPI at 35 g ha−1 followed by 35 g ha−1 at GC. Except for common ragweed, weed control with this treatment was similar to that by the standard. Peanut yield and net returns with this treatment were similar to those with the standard at three of four locations.

Interactions of fluazifop-P, sethoxydim, clethodim, and quizalofop-P with DPX-PE350 were evaluated. DPX-PE350 at 110 g ae ha−1 reduced control of large crabgrass when mixed with all graminicides and control of broadleaf signalgrass when mixed with fluazifop-P or quizalofop-P. Increasing the rate of graminicide reduced or eliminated antagonism. Applying sethoxydim and DPX-PE350 sequentially eliminated antagonism on large crabgrass. Control of seedling johnsongrass by the graminicides was not reduced by DPX-PE350. DPX-PE350 reduced control of rhizomatous johnsongrass by sethoxydim. Graminicides had no effect on entireleaf morningglory control with DPX-PE350.

The influence of weed seed burial depth on seedling emergence is a common and important topic in undergraduate weed science courses. A laboratory exercise was developed at Iowa State University to actively demonstrate changes in weed seedling emergence with increased seed-burial depth. Twenty-five ivyleaf morningglory and wild mustard seeds were sown in pots in monoculture, and the number of emerging seedlings was counted for 3 wk. The results from two semesters were analyzed to determine whether the experiment was successful in meeting its intended outcomes. Assessment of student perceptions and attitudes indicated that the activity increased students' understanding of weed biology; improved students' critical thinking, reading, and writing skills; and improved students' ability to make scientific observations, interpret graphical information, and analyze and summarize research data.

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.