The sorption of two sulfonylurea herbicides (SU), metsulfuron methyl and nicosulfuron, on pure clays and organoclays was investigated. Three clays (Arizona smectite, SAz-1, Wyoming smectite, SWy-2, and hectorite, SHCa-1), were treated with amounts of octadecylammonium (ODA) or dioctadecyldimethylammonium (DODMA) cations equal to ∼50 and 100% of the clays’ cation exchange capacity (CEC). Sorption isotherms were fitted to the Freundlich equation. While no measurable sorption was found on the pure clays (Kf = 0), organoclays prepared using both primary and quaternary amines were effective as SU sorbents. The metsulfuron methyl Kf values ranged between 196 and 1498 µmol1−1/n kg−1 L1/n, and Kf values for nicosulfuron, which were lower than those of metsulfuron methyl, ranged from 35 to 198 umol1−1/n kg−1 L1/n. As shown by sorption coefficients, Kd and KOC, SWy-2 treated with DODMA at ∼100% of the CEC was the most effective sorbent for metsulfuron, Kd = 684 L kg−1 and KOC = 2138 L kg−1. For nicosulfuron the most effective sorbent was SAz-1 with ODA at ∼ 50% of the CEC (Kd = 147 L kg−1 and KOC = 1233 L kg−1). In contrast to other weak-acid herbicides, such as phenoxy and picolinic acids, no clear relationships were found between sorption and layer charge, organic carbon content, and basal spacing of the organoclays for both sulfonylurea herbicides. Sorption of both herbicides on organoclays was assumed to involve hydrophobic and polar interactions for which the availability of interlayer room between organocations was a very important factor.

Annual sedge (Cyperus compressus L.) populations with resistance to halosulfuron were identified in turfgrass at two new locations in Georgia. Research was conducted to evaluate (1) resistance levels to two acetolactate synthase (ALS) inhibitors, (2) ALS enzyme susceptibility, (3) genetic differences associated with resistance, and (4) differential levels of ALS gene expression in these biotypes. In dose–response experiments, the biotypes were >160 times resistant to halosulfuron but only 12 times more resistant to imazaquin compared with a susceptible biotype. In vitro enzyme assays indicated that resistant (R) biotypes required 6.1-fold greater concentrations of imazaquin to reduce ALS activity 50% compared with the susceptible (S) biotype. Both R biotypes had a similar Pro-197-Ser amino acid substitution in the ALS gene that confers resistance to sulfonylureas. Compared with the S biotype, R biotypes had 4.4 times higher ALS gene expression than the S biotype. No differences in gene copy number were found between any biotypes for the ALS gene. Overall, ALS-resistant C. compressus selected by halosulfuron use in turfgrass may be exhibiting partial susceptibility to imazaquin but complete resistance to sulfonylureas. Differential levels of susceptibility to ALS inhibitors for these biotypes are associated with the Pro-197-Ser substitution and enhanced expression of the ALS gene.

Purple nutsedge is difficult to control in vegetable plasticulture due to its ability to penetrate the plastic mulch. Experiments were conducted in Spring 2011 and 2012 at the Plant Science Research and Education Center in Citra, Florida, and in Spring and Fall 2013 at the Gulf Coast Research and Education Center in Balm, Florida. The objective was to determine tomato (cv. Amelia, Charger, and Florida 47) tolerance and purple nutsedge response to herbicides and herbicide tank-mixes applied POST-directed to base of tomato. Chlorimuron-ethyl, flazasulfuron, fomesafen, halosulfuron, imazosulfuron, rimsulfuron, nicosulfuron, and trifloxysulfuron applied POST-directed to the base of the crop did not cause crop damage. Halosulfuron or tank-mixes that contained halosulfuron tended to provide the greatest nutsedge suppression in all experiments. Halosulfuron or nicosulfuron+rimsulfuron applications when tomato (cv. Charger) were flowering reduced marketable yields by 22-28% compared to the nontreated control. No yield reductions occurred with Florida 47 or Amelia cultivars. Flazasulfuron provided similar purple nutsedge suppression to halosulfuron and did not damage tomato. Tank-mixes that contained halosulfuron tended not to provide any added benefit over halosulfuron alone. This research identified herbicides that are safe for use as a POST-directed application in tomato. Additional research is needed to evaluate efficacy of these herbicides on broadleaf weeds.

During 1990, injury to tomatoes grown on the narrow land between the Albufera Lake (Spain) and the Mediterranean Sea was attributed to use of irrigation water coming from adjacent rice fields containing bensulfuron and quinclorac. A tomato root bioassay was developed to detect the herbicides in 10 ml of water. The assay was more sensitive to bensulfuron (0.5 ng ml−1) than quinclorac (100 ng ml−1). Only 30 ml of the affected water are necessary to conduct the test. Albufera water, sampled at three sites during 1991 and one during 1992 in the irrigation network canals caused different tomato main root length responses.

A pot bioassay, based on root growth of pregerminated corn, was used to evaluate factors influencing field persistence of chlorsulfuron, metsulfuron, triasulfuron, and tribenuron, which were applied preemergence at 0, 10, 20, and 40 g ai ha−1 to wheat grown in three soils that differed in texture (sandy loam, sandy clay loam, and silty clay loam) and pH (7.9, 4.7, and 7.6). Residual activity and leaching of all herbicides in all soils increased with increasing rate of application, with the exception of tribenuron which showed practically no residual activity and leaching in sandy clay loam soil. Sunflower sown 4 mo after tribenuron application in all soils was not injured by any rate used but was significantly affected by the other herbicides. Lentil and sugarbeet also were affected by all herbicides in all soils. These three crops sown 8 mo after herbicide application were not affected by any herbicide used in the sandy clay loam soil but were injured by chlorsulfuron, triasulfuron, and metsulfuron in the sandy loam soil. Only lentil and sugarbeet were injured by chlorsulfuron in the silty clay loam soil.

Hydrolysis and adsorption of the sulfonylurea herbicides rimsulfuron and primisulfuron were investigated under laboratory conditions. Degradation in aqueous solutions was determined between pH 3 and 8 and between 5 and 35 C. Rimsulfuron degraded faster than primisulfuron. Half-lives at different temperatures at pH 4 ranged from 0.16 to 5.8 d for rimsulfuron and from 0.47 to 16.1 d for primisulfuron. Primisulfuron hydrolysis at 30 C decreased with increasing pH, but rimsulfuron decreased up to pH 7, then increased, suggesting rapid degradation in alkaline conditions. Adsorption, measured in six Colorado soils, was complete within 2 h in all soils. Adsorption isotherms were determined by batch equilibration of 75 to 600 μg L−1. Rimsulfuron was adsorbed in amounts 3.7 to 7 times higher than primisulfuron, with adsorption distribution coefficients (Kd) ranging from 0.1 to to 1.18 for primisulfuron and from 0.71 to 5.1 for rimsulfuron. Adsorption of both herbicides was slightly correlated with soil clay content, and primisulfuron adsorption was also correlated with organic matter content.

Parasitic witchweeds inflict most of their damage while still underground and attached to crop roots. Most selective translocated herbicides are detoxified by crops such as corn and thus cannot reach the attached parasites. Corn with target site resistance to acetolactate synthase (ALS)-inhibiting herbicides was tested to ascertain whether these herbicides could control witchweeds, assuming that witchweeds do not obtain amino acids from the crop. Postemergence directed sprays of 27 g ae ha−1 imazapyr 54 d after planting (DAP) delayed Striga asiatica emergence on corn in South Carolina from 3 wk (control) to 7 wk and to 11 wk when mixed with 45 g ae ha−1 AC 263 222. Treatments with up to 71 g ae ha−1 imazamox, and up to 71 g ae ha−1 AC 263 222 only delayed Striga emergence by 1 wk, and 71 g ae ha−1 imazethapyr was ineffective. ALS-inhibiting herbicides were far more effective when applied in 1-ml drenches above the seed at planting. Chlorsulfuron (10 g ai ha−1) and sulfometuron (50 g ai ha−1) were somewhat phytotoxic to Pioneer 3245IR. Rimsulfuron (30 g ai ha−1), metsulfuron (10 g ai ha−1), halosulfuron (120 g ai ha−1), and imazethapyr (140 g ae ha−1) were marginally active in Kenya, with some mature Striga hermonthica seed-bearing capsules appearing at harvest (12 wk). Imazapyr at 15 g ae ha−1 gave 70 to 95% suppression of capsule formation, whereas no capsules appeared at 30 g ae ha−1. The use of imazapyr in Kenya increased the harvest index by 17% when corn plants in Striga-infested soils were kept insect and disease free by using insecticides and fungicides. Thus, complete control can be achieved at affordable cost by farmers in subsistence conditions.

Solution pH from 6.0 to 8.0 did not affect the germination of Italian ryegrass, ‘Pensacola bahiagrass,’ or common bermudagrass grown in petri dishes in growth chambers. Seeding intervals following metsulfuron methyl application varied from species to species and between soil types. Greenhouse studies indicated that in an Okolona silty clay, common bermudagrass should not be planted until 12 wk after metsulfuron methyl application. Italian ryegrass showed no metsulfuron methyl injury at the 6-wk sampling date when no lime was added, indicating reseeding was feasible at this time; however, a 12-wk time interval was not sufficient when lime was applied. Pensacola bahiagrass was injured when reseeded at 12 wk, regardless of liming rate. In a Prentiss fine sandy loam soil, common bermudagrass could be reseeded 12 wk after application when no lime was added, but not when lime was added. Italian ryegrass and Pensacola bahiagrass should not be reseeded for at least 12 wk, regardless of lime rate. Field experiments, where metsulfuron methyl was applied to the field and seeding was carried out in the greenhouse, indicated on the Okolona silty clay that common bermudagrass reseeding could occur at all liming rates after 3 wk, and Italian ryegrass and Pensacola bahiagrass after 6 wk. In the Prentiss fine sandy loam, common bermudagrass reseeding could occur at 3 wk, regardless of lime rate. Italian ryegrass emergence was not affected when reseeded immediately after metsulfuron methyl application, but height was reduced for longer periods, and increased lime rate lengthened this interval. Pensacola bahiagrass reseeding was feasible at 3 wk.

Response of flax, canola, field pea, sunflower, field corn, lentils, and common buckwheat to soil residues of CGA-131036 and chlorsulfuron applied at 22 g ai ha–1 was determined on two soil types at Morden, Manitoba. on a fine sandy loam with a pH of 7.4 and 4.5% organic matter, the length of time required before crops showed no phytotoxicity from CGA-131036 residues was: sunflower 4 yr; canola and common buckwheat 3 yr; flax 2 yr; field pea and field corn 1 yr. on a clay loam with a pH of 6.5 and 5.3% organic matter, the corresponding duration was: lentil, canola, and sunflower 3 yr; flax and field pea 1 yr. Chlorsulfuron residues persisted somewhat longer than CGA-131036 residues on the sandy loam but not on the clay loam.

Giant foxtail, woolly cupgrass, and wild-proso millet infest millions of hectares of land devoted to corn production in the midwestern U.S. Control of these species and effects on corn grain yield were evaluated at various timings using POST applications of nicosulfuron vs. applications of various PRE herbicides at 17 locations across the midwestern U.S. in 1992 and 1993. Nicosulfuron applied to 5 to 10 cm giant foxtail and woolly cupgrass provided greater control than that observed with selected PRE herbicides. Giant foxtail control with nicosulfuron averaged 88%, and control of woolly cupgrass averaged 77% across all sites. Nicosulfuron, applied to 5 to 10 cm wild-proso millet, provided a level of control similar to that of selected PRE herbicides. Corn grain yield was greater when giant foxtail was controlled POST with nicosulfuron vs. PRE control with selected soil-applied herbicides. Corn grain yields were similar when nicosulfuron was applied POST to 5 to 10 cm woolly cupgrass or wild-proso millet vs. PRE control of these grass weeds. Across a broad range of geographical locations, nicosulfuron, applied POST to 5 to 10 cm tall grass, provided greater or similar levels of weed control vs. the selected PRE herbicides, with no deleterious effect on grain yield.

Chlorimuron dissipation as determined by bioavailability in nine soils across the Southern United States was characterized by rapid initial loss followed by a slower dissipation rate following field application of the herbicide in soybean. The rate of bioavailable dissipation varied by year and soil The calculated time for 50% dissipation of bioavailable chlorimuron (DT50) ranged from 5 to 18 d in 1988, 5 to 20 d in 1989, and 5 to 11 d in 1990. In 2 of 3 yr, chlorimuron DT50 was positively correlated with temperature 24 h after application. Chlorimuron DT50 was positively correlated with precipitation in 1988 when regional rainfall was below normal and negatively correlated with precipitation 30 d after application in 1989 when regional rainfall was above normal.

The control of three summer annual grass weeds with herbicides during establishment of forage grasses was studied near Concord and Mead, NE, in 1984, 1985, and 1986. Three cool-season forage grasses, intermediate wheatgrass, tall fescue, and smooth bromegrass, and two warm-season grasses, big bluestem and switchgrass, were included. The control of three major summer annual grasses, green foxtail, barnyardgrass, and large crabgrass, was excellent with fenoxaprop at 0.22 kg ai/ha. Slight to moderate injury to cool-season forage grasses and severe injury to warm-season grasses were evident. Sethoxydim at 0.22 kg ai/ha and haloxyfop at 0.11 kg ai/ha controlled green foxtail and large crabgrass, but not barnyardgrass. Sulfometuron-treated big bluestem and switchgrass plots had the best forage stand frequencies and yields and, at the rate used, sulfometuron satisfactorily controlled green foxtail but only marginally controlled barnyardgrass and large crabgrass.

Greenhouse and field experiments were conducted to evaluate the effectiveness of nicosulfuron and primisulfuron with different adjuvants on wirestem muhly control. The adjuvants evaluated with the two herbicides included a nonionic surfactant, crop-oil concentrate, crop-oil concentrate plus urea-ammonium nitrate, methylated vegetable-oil concentrate, and organosilicone methylated vegetable-oil concentrate. In the greenhouse, nicosulfuron and primisulfuron performance was similar, although small differences occurred between adjuvants and herbicides. In the field, changing adjuvant affected nicosulfuron performance more than primisulfuron and in general, greater control was achieved with nicosulfuron than with primisulfuron. Among adjuvants, methylated vegetable-oil concentrate provided greater wirestem muhly control with nicosulfuron and sometimes primisulfuron compared to the others, while the nonionic surfactant was the least effective with both herbicides. Regardless of adjuvant, none of the field-applied treatments controlled wirestem muhly much beyond the 12 wk-evaluation period.