A 4.6-m-long, segmented, flexible-pipe ropewick applicator was constructed to apply picloram (4-amino-3,5,6-trichloropicolinic acid) to leafy spurge (Euphorbia esula L. ♯ EPHES) and other weed species. Gauge wheels on each ropewick applicator segment permit height adjustments, and a loose, independent, vertical flexing action permits the segments to effectively traverse depressed or raised areas. The applicator was designed for use in pastures with rough, uneven terrain where it is difficult to uniformly wipe herbicide solution on plants with a rigid-pipe ropewick. The applicator was found to be durable and effective in applying picloram to leafy spurge.

The rates of degradation of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] were determined in an untreated Portneuf silt loam, in soil with added organic amendments, and in soil previously treated with metribuzin. While first-order rate kinetics generally described the degradation of the metribuzin in the soil, a quadratic expression was superior. Organic amendments were found to inhibit or accelerate the rate of breakdown of metribuzin depending upon the kind of amendment. Neither a lag phase nor an enrichment was observed from prior treatment with metribuzin.

The effect of various soil parameters on metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] efficacy was studied on seven soils and metribuzin adsorption was investigated in nine soils. Soil organic-matter and clay contents were correlated with metribuzin activity. Specific surface area, as measured by ethylene glycol monoethyl ether (EGME) was highly correlated with metribuzin activity. Soil organic-matter content and EGME surface area measurements were also highly correlated with metribuzin adsorption in soils. Since metribuzin is highly water soluble (water solubility greater than 1000 ppm), it was probably adsorbed at the hydrophilic sites on the soil surfaces that were measured by EGME. Metribuzin was much more mobile than atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] in a leaching study.

Field studies were conducted in 1981 to 1983 to evaluate selected herbicides for control of a natural infestation of woolly croton (Croton capitatus Michx. ♯ CVNCP) in soybean [Glycine max (L.) Merr.]. Ineffective woolly croton control was obtained with all preemergence herbicides evaluated. Early postemergence treatments of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} and lactofen {1-(carboethoxy)ethyl) 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate} provided excellent woolly croton control. Postdirected applications of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] applied at the V4 stage of soybean growth and tank mixes of cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea], or metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] plus 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] applied at the V4 and repeated at the V6 stage of soybean growth also provided effective control.

Pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} was hand broadcast at 2.2 and 4.5 kg ai/ha every month for 2 yr on an area infested with live oak (Quercus virginiana Mill. ♯4 QUEVI), post oak (Q. stellata Wangenh. ♯ QUESL), parsley hawthorn (Crataegus marshallii Egglest. ♯ CSCMS), and yaupon (Ilex vomitoria Ait. ♯ ILEVO) on the Gulf Coast Prairie near Cordele, TX. Live oak, post oak, and parsley hawthorn trees were killed at most rates and dates of tebuthiuron application. Applications of 2.2 kg/ha of tebuthiuron killed 90% or more of the yaupon plants when it was applied in October and December 1975 and February, March, and June 1976 and less than 90% when applied at other dates. On another site, pelleted tebuthiuron was aerially applied at 2.2 and 4.5 kg/ha every 3 months during 1978 and 1979 in the Post Oak Savannah near Bryan, TX. At 2.2 kg/ha, tebuthiuron killed all post oak and 80% or more of the blackjack oak (Q. marilandica Muechh.), yaupon, winged elm (Ulmus alata Michx. ♯ ULMAL), and mockernut hickory (Carya tomentosa Nutt.) regardless of date treated. Tree huckleberry (Vaccinium arboreum Marsh.) killed by tebuthiuron when applied at 2.2 kg/ha ranged from 34% in July 1979 to 69% from application in February 1978. Application of 4.5 kg/ha of tebuthiuron killed 83% or more of the tree huckleberry when it was applied in January and April 1978 and January, April, July, and October 1979. Herbaceous plant cover usually increased by the second season.

Yaupon (Ilex vomitoria Ait. ♯ ILEVO) in the Post Oak Savannah of Texas was treated with liquid and dry formulations of herbicides. Sprays of Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazol-2-yl]-N, N′-dimethylurea} and picloram (4-amino-3,5,6-trichloropicolinic acid), sprays and pellets of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and boluses of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1N,3H)-dione] at 4.5 kg ae or ai/ha were the most effective treatments, reducing the canopy 87 to 99% and killing 68 to 93% of the yaupon after 2 yr. The percentage of dead yaupon after 1 yr was similar to that found 2 or 3 yr after treatment. Most herbicides, except clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), reduced the yaupon canopy sufficiently to allow an increase in understory grass and broadleaf vegetation, particularly 1 yr after treatment.

An isolation and screening procedure was developed to identify soil actinomycetes that can produce germination and growth inhibitors on agar plates. Eight of 120 isolates tested demonstrated severe toxicity on cress (Lepidium sativum L. ‘Curly’) and barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG]. Several isolates were observed to stimulate growth. In replicated tests using the agar screening procedure, compounds produced by microorganisms significantly inhibited germination and growth of indicator plants. Organisms shown to produce toxins in agar media did not always produce toxins when grown in submerged culture.

After 45 weeks, between 5 and 8% of the applied radioactivity from 14C-chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} applied to small sandy loam plots was recovered as chlorsulfuron and about 15% as 2-chlorobenzenesulfonamide. After 95 weeks, 2% of the original radioactivity remained as chlorsulfuron and 20% as the sulfonamide. The persistence of formulated chlorsulfuron was investigated using small field plots at two locations for three successive years. Between 3 and 16% of the herbicide applied during May was detected in the top 10-cm soil layers the following May using a corn-root (Zea mays L.) bioassay procedure.

Bioassay techniques were evaluated for the determination of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} residues in soil and water. A linear response of corn (Zea mays L.) primary root length to chlorsulfuron concentrations (InX+1) of 0.0 to 16.0 μg/L was observed in the water bioassay. Several soil extraction bioassay methods were attempted and found to be highly variable. A Ca(OH)2 soil extraction bioassay technique produced a linear response of primary corn root length to chlorsulfuron concentrations ranging from 0.0 to 64.0 μg/kg. The efficiency of the Ca(OH)2 extraction bioassay was determined by the use of 14C-chlorsulfuron. Recovery efficiency at 1.0 μg/kg was 74% and averaged 62% at all higher chlorsulfuron concentrations.

The sweet potato [Ipomoea batatas (L.) Lam.] cultivars ‘Jewel’, ‘Centennial’, ‘Caromex’, and breeding lines ‘W-70’, ‘W-152’, and ‘Tinian’ (PI 153655) were evaluated for metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as–triazin5(4H)-one] tolerance in greenhouse and field studies. Tinian was the most tolerant line. Its yields were not reduced by 2.2 kg/ha metribuzin in the field. Jewel, Centennial and W-152 were intermediate in response to metribuzin, and W-70 and Caromex were most susceptible. Regression analyses indicated a high correlation between the response of sweet potato cultivars to 0.5 ppm metribuzin incorporated in a potting mix in the greenhouse and their response to 1.1 kg/ha metribuzin applied after transplanting in the field.

Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] adsorption was positively correlated with soil organic-matter content, clay content, and surface area as measured by ethylene glycol monoethyl ether (EGME) or benzyl ethyl ether (BEE) and inversely correlated with herbicidal activity. Alachlor was adsorbed in slightly greater amounts by soil than metolachlor. Metolachlor had slightly greater bioactivity than alachlor on grass weeds, but the herbicides had similar activity on broadleaf weeds. Slightly greater amounts of metolachlor than alachlor were leached through a Norfolk soil and slightly greater amounts of alachlor were retained in the upper soil zones, compared with metolachlor.

The release of soil-bound 14C-prometryne [N,N′-bis(l-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine] residues was affected by soil pH, fertilizer treatments (with or without plants), and the crop species wheat [Triticum aestivum (L.) Merr. ‘Marquis’] and soybean [Glycine max (L.) Merr. ‘Maple Presto’]. More of the bound radioactivity was released following large pH changes in the soil than with small deviations. In addition, more 14C-prometryne was found in the extracts of the soil incubated with large pH alterations. Fertilizing with ionic nitrogen sources (NO3– and NH4+) in the absence of plants was also responsible for releasing higher levels of radioactivity than with the nonionic fertilizer urea. These fertilizer-induced differences in release were not apparent when wheat plants were added to the system. Release of the bound radioactivity, however, was plant specific, particularly in the rhizoplane, since soybean roots elicited a greater release in the rhizoplane than wheat roots. Transport and metabolism of these residues were also plant specific.

Emergence of sugarbeets (Beta vulgaris L. ‘MonoHy D2’) from soil was reduced by germinating kochia [Kochia scoparia (L.) Schrad. ♯ KCHSC] seed at densities greater than 1 seed/cm2 when the fungus Rhizopus sp. was present. Water-soluble exudates from germinated kochia seed did not influence Rhizopus growth in vitro or sugarbeet germination. Cell-free culture extracts of Rhizopus reduced sugarbeet germination and radicle elongation. There appeared to be an interaction between kochia and Rhizopus, but the responsible compounds were not identified.

Adsorption of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl] benzenesulfonamide} on four soils having different pH values (6.2 to 8.1) was low. Log/log Freundlich isotherms for all soils at 8 and 30 C were linear, the extent of adsorption being greater at 8 than at 30 C. There was an inverse relationship between pH and degradation rate with a half-life of 88.5 days at pH 6.2 and 144 days at pH 8.1 at 20 C. Rapid disappearance was noted during the first 15 days after application. With decreasing moisture and temperature, chlorsulfuron degraded more slowly. The half-life ranged from 229 days at 10 C and moisture content of 75% field capacity to 62.5 days at 40 C and 75% field capacity at pH 7.7.

The importance of including crop density in studies of weed-wheat competition and in making estimates of crop losses due to weeds was demonstrated. Wheat density in adjacent quadrats of 1 m2 varied by an average of 25 plants in the farm fields and research plots examined. Differences between adjacent quadrats were in the same range for fields sown with different implements. Yield per plant, dry weight per plant, and tillering per plant decreased with increasing wheat density. For weed-crop competition studies in small-grain crops, the yields of weed-free and weedy quadrats are normally compared to estimate crop loss caused by competition. It was demonstrated that such estimates can be highly distorted if crop density is not taken into account. Current procedures used widely in agronomic competition studies are inadequate to properly define the relationship between crops and weeds. A more accurate method for performing such investigations is described in which both weed and crop abundance are determined. These variables are related to crop loss using multiple regression.

The chemical composition and the utilization by domestic goats (Capra hircus L. ‘Saanen’) of alfalfa (Medicago sativa L.) hay and silage that contained or did not contain hoary alyssum [Berteroa incana (L.) DC. ♯ BEFIN] was studied. Alfalfa was higher in quality than hoary alyssum; crude protein (CP) was 38% higher, and the neutral- and acid-detergent fiber (NDF and ADF) were 18 and 29% lower, respectively. Less CP and more ADF were found in weedy hay than in other forages. Animal utilization, as measured by the dry-matter intake, digestible dry-matter intake, relative intake, and nutritive value index were greater for weed-free than for weedy forages. Hoary alyssum was more deleterious in chopped silage than in long hay, because of selective refusal of the weed by goats that were fed hay. The presence of hoary alyssum in alfalfa decreased its utilization by ruminants.

Flurazole [phenylmethyl 2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylate] and acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide] were examined in the laboratory and greenhouse for effects on grain sorghum [Sorghum bicolor (L.) Moench ‘G-522 DR’]. Flurazole did not protect against acetochlor-induced inhibition of primary root growth when sorghum was grown in distilled water, but some safening occurred after 8 days when nutrients were available. Flurazole did not protect primary roots completely. In the presence of nutrients, however, flurazole stimulated growth of the mesocotyl roots and protected the second adventitious root system.

Degradation of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-yl)amino] carbonyl] benzenesulfonamide} in acidic and alkaline soils was evaluated using plant bioassay and high-performance liquid chromatography (HPLC) radiotracer techniques. Soil sterilization with either ethylene oxide (Et0) or gamma irradiation significantly reduced breakdown of chlorsulfuron; the ability for degradation was restored by reinoculation with indigenous soil microorganisms. Streptomyces griseolus (a soil actinomycete), Aspergillus niger, and Penicillium sp. (soil fungi) were demonstrated to degrade 14C-chlorsulfuron in pure culture. In addition to microbial breakdown, chemical hydrolysis was an important factor in the disappearance of chlorsulfuron from soil. The contribution of chemical hydrolysis to total degradation was a function of soil pH, with hydrolysis occurring most rapidly in acidic soils. Both dissipation processes slowed markedly at low temperatures.