Field experiments conducted over a 7-yr period have demonstrated that common buckwheat (Fagopyrum esculentum Moench. cv. ‘Mancan’) has acceptable tolerance to many herbicides that are known to selectively control grass-type weeds in broadleaf crops. Herbicides for broadleaf weed control that showed some selectivity in common buckwheat were desmedipham {ethyl [3-[(phenylamino) carbonyl] oxy] phenyl] carbamate} applied postemergence and fluorochloridone {3-chloro-4-(chloromethyl)-1-[3-(trifluoromethyl)phenyl]-2-pyrrolidinone} applied either preplant soil incorporated or preemergence shallow incorporated. Tank mixtures of desmedipham plus sethoxydim {2-[1-(ethoxyimino)butyl-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} also showed adequate tolerance to common buckwheat at rates recommended for weed control in other crops.

Various chemical treatments were evaluated over two growing seasons for control of triazine-resistant common lambsquarters (Chenopodium album L. # CHEAL) and for control of a triazine-resistant infestation containing both redroot pigweed (Amaranthus retroflexus L. # AMARE) and Powell amaranth (A. powellii S. Wats. # AMAPO). Atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] provided unsatisfactory control of these biotypes. Satisfactory control of common lambsquarters was obtained with preemergence applications of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] or dicamba (3,6-dichloro-2-methoxybenzoic acid), or postemergence applications of dicamba, bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), or bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Satisfactory control of pigweed was obtained with preemergence applications of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] or postemergence treatments of dicamba, bromoxynil, or 2,4-D [(2,4-dichlorophenoxy) acetic acid].

Established stands of alfalfa (Medicago sativa L.) at two field locations were treated at one date in the fall with pronamide [3,5-dichloro (N-1,1-dimethyl-2-propynil) benzamide] at 0.8 and 1.6 kg ai/ha and at two dates in the spring with sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.3 and 0.6 kg ai/ha for the control of quackgrass [Agropyron repens (L.) Beauv. # AGRRE]. Herbicide efficacy was compared by measuring botanical and chemical composition and yield of forage. Both chemicals suppressed quackgrass in first-cutting herbage. While sethoxydim at the higher rate was equivalent to pronamide for increasing the proportion of alfalfa in forage, pronamide was superior for increasing seasonal total yield. Late postemergence applications of sethoxydim were more effective for quackgrass regrowth control than earlier spring applications. Controlling quackgrass in late spring resulted in lower crude protein (CP) content in first-cutting forage than did controlling it in fall. Alfalfa competing with untreated quackgrass had a lower CP content than where quackgrass was controlled with herbicides. All herbicide treatments reduced the neutral-detergent fiber (NDF) of the herbage. As measured by the acid-detergent fiber (ADF) concentration of alfalfa, sethoxydim slightly retarded spring growth of the legume.

Corn (Zea mays L.) grain yield was measured in a 5-yr study at two locations in central Ohio in relationship to johnsongrass [Sorghum halepense (L.) Pers. # SORHA] populations infesting the plots. Herbicide treatments were EPTC + R-25788 (S-ethyl dipropyl carbamothioate) + (N,N-diallyl-2,2-dichloroacetamide) at 6.7 kg ai/ha to corn in a monoculture and in a 3-yr rotation of winter wheat (Triticum aestivum L.), corn, and soybeans [Glycine max (L.) Merr.], with each crop being grown each year. There were large increases in johnsongrass populations in the monocultures during the course of the 5-yr study, and corn grain yield fell to zero, even though ear formation was not greatly reduced. Conversely, johnsongrass populations in the rotation were low and maize grain yields and numbers of ears remained high. The differential in grain yields between the two treatments was apparently due chiefly to lack of pollination or kernel development, since ears were formed in approximately equal numbers, except for the last year.

A 3-yr study was initiated in 1982 to determine the effects of herbicides and crop rotations on large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] and broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash # BRAPP] population dynamics. Regardless of the crop rotation sequence, broadleaf signalgrass immediately became the predominant weed where standard herbicide programs were used. Large crabgrass became the predominant species after two growing seasons if no herbicides were applied. Domination by large crabgrass appeared to be due to greater seed production. The domination by broadleaf signalgrass in plots treated with herbicides was attributed to its tolerance to the primary grass herbicide alachlor [2-chloro-N-(2,6-diethylphenyl)-N-methoxymethyl)acetamide]. Broadleaf signalgrass emergence from soil treated with 2.2 kg ai/ha was not statistically different from that in untreated soil, while large crabgrass and fall panicum [Panicum dichotomiflorum (L.) Michx. # PANDI] emergence was significantly reduced at the same rate.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} is used to control weedy grasses in red fescue (Festuca rubra L. # FESRU and F. rubra ssp. commutata), an important seed crop in Oregon. The sethoxydim rate required to reduce growth rate of 11 cultivars of red fescue and four cultivars of bentgrass (Agrostis tenuis Sibth. # AGSTE and A. stolonifera L. var. palustris # AGSST), a common contaminant in red fescue fields, by 50% (GR50) was determined in greenhouse and laboratory experiments. Field experiments compared only red fescue cv. ‘Pennlawn’ and bentgrass cv. ‘Penncross'. The GR50 values for Pennlawn red fescue in the field, the greenhouse, and the laboratory were 30 kg ai/ha, 15 kg/ha, and 5300 μM, respectively. Penncross bentgrass was approximately 400, 1400, and 12 900 times more susceptible than Pennlawn red fescue in the field, in the greenhouse, and in laboratory experiments, respectively. Plants were at different growth stages in the different experiments. The xylene and surfactant used as a solvent for the technical grade sethoxydim was as toxic to red fescue without sethoxydim as when sethoxydim was included. Cultivars of red fescue differed in their response to sethoxydim, but cultivars of bentgrass did not. The GR50's of other species tested in the greenhouse were >4 kg/ha for annual bluegrass (Poa annua L. # POAAN), 0.22 kg/ha for tall fescue (F. arundinacea Schreb. # FESAR), 0.37 kg/ha for downy brome (Bromus tectorum L. # BROTE), and 0.017 kg/ha for Italian ryegrass (Lolium multiflorum Lam. # LOLMU).

Experiments were conducted at Urbana, IL, in 1983 and 1984 to determine the effect of adjuvants, adjuvant rate, and carrier volume on postemergence weed control with bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} in soybeans [Glycine max (L.) Merr. ‘Williams’]. Little difference was observed between a petroleum oil:emulsifier blend (83:17, v/v) (POC) and a soybean oil: emulsifier blend (85:15, v/v) (SBOC) in enhancing control of velvetleaf (Abutilon theophrasti Medik. # ABUTH) with 0.6 or 1.1 kg ai/ha bentazon. Application of bentazon in a carrier volume of 94 L/ha provided velvetleaf control equivalent to that applied in 187 L/ha. Increasing the adjuvant rate from 2.3 to 11.7 L/ha increased visible soybean injury but had no effect on velvetleaf control with bentazon. Control of giant foxtail (Setaria faberi Herrm. # SETFA) with 0.1 kg ai/ha sethoxydim was enhanced more by POC than by SBOC. Phytotoxicity of sethoxydim was not altered by changes in carrier volume or adjuvant rate under conditions of adequate soil moisture in 1983. Under limiting soil moisture in 1984, giant foxtail control with sethoxydim increased slightly when the adjuvant rate was increased from 4.6 to 11.7 L/ha, and carrier volume was increased from 47 to 187 L/ha.

Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], when applied pretransplant at 0.28 kg ai/ha, killed peppers (Capsicum annuum L.) that were transplanted bare root or in plugs. Activated carbon applied at 1 g/plant effectively reduced injury of such peppers in soils treated with up to 0.56 kg ai/ha metribuzin. The increase in crop tolerance to metribuzin was dependent on the amount of activated carbon added. The level of crop protection for plug transplants depended on the amount of activated carbon per plant rather than on the percentage in the greenhouse mix by dry weight. One gram was required to protect plug transplants grown in cells that held 10 or 20 g of greenhouse mix.

The effects of twelve soil metabolites of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] on soybean [Glycine max (L.) Merr.] growth, yield, and seed oil and protein content were determined. The metabolites included oxidative dealkylated, reduced nitro group, benzimidazole, azoxy, azo, oxidized, and hydroxylated derivatives of trifluralin. When applied at 0.22 kg ai/ha and incorporated 7.5 cm deep, no individual metabolite had a significant adverse effect on growth or yield. Three of the metabolites significantly decreased seed oil content and two of the metabolites significantly increased seed protein content. These effects are not considered important in that the differences, while statistically significant, are very small. Also, the amounts of metabolites applied greatly exceeded those expected to be found after many years of continuous use of trifluralin. Potential accumulation of individual metabolites from long-term use of trifluralin does not appear to adversely affect soybean growth, yield, or quality.

The dissociation constant for chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in aqueous solution measured by spectrophotometric titration is 3.58 ± 0.05. Chlorsulfuron was more strongly adsorbed on IRA-400-Cl strong anion exchange resin than on IR-4B-OH weak anion exchange resin or Al2O3 anionotropic adsorbent. Hydrogen bonding was probably responsible for the adsorption observed on IR-120-Na(H) cation exchange resin. No chlorsulfuron was adsorbed on Al2O3 cationotropic absorbent, technical montmorillonite, illite, or kaolinite. Adsorption did occur on organic matter derived from a histosol. Chlorsulfuron was strongly adsorbed on activated charcoal but had little affinity for α-cellulose. Adsorption onto hydrophobic polymeric XAD-2 adsorbent at pH 5.2 was not significant for chlorsulfuron concentrations below 30 μM. No significant adsorption occurred on a variety of mineral soils low in organic matter. Adsorption on a Sharpsburg silty clay loam was inversely related to solution pH. Hydrogen bonding and charge transfer bonds were postulated as the major mechanisms responsible for chlorsulfuron adsorption in soil.

In bioassays, rice (Oryza sativa L.) recovery from metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] injury tended to be slower in flooded rice, but was not significantly different from the recovery rate in a nonflooded rice. In soils treated with 1 ppm (w/w) metolachlor and incubated in constant-temperature chambers, the half-life of metolachlor was shorter at 40 C than at 30 C. The degradation rate of metolachlor was not significantly correlated with declining moisture potentials in the range of −30 to −80 kPa. The CO2 evolution from metolachlor-treated soil was negatively correlated with incubation time and positively correlated to declining moisture levels. In a field study, metolachlor, as determined by bioassay, was mobile in a Taloka silt loam soil profile. After being incorporated to 7.5 cm, it became evenly distributed in the top 15 cm of the soil profile within 18 days. Metolachlor adsorption was positively correlated with clay and organic carbon content.

In a test of laboratory precision and accuracy, streamwater samples fortified with 0, 10, or 50 μg ae/L 2,4-D [(2,4-dichlorophenoxy)acetic acid] and picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) were submitted in quadruplicate for residue analysis to 10 laboratories that analyze samples for a fee. Varying amounts of the herbicides were detected by eight laboratories, and two reported no residues. Analyses from most laboratories had a negative bias (ranging from −2 to −92%), although a positive bias appeared in a few instances. Precision was highly variable, the coefficient of variation ranging from 3.4 to 200%. The accuracy range in 19 of 20 cases was ±100 to ±78% for 10 and 50 μg/L 2,4-D and ±100 to ±114% for 10 and 50 μg/L picloram, respectively. Results show that careful selection of contract laboratories and a quality assurance program should be part of monitoring for water contamination with herbicides.