Birdsfoot trefoil (Lotus corniculatus L.) was direct-seeded into five different grass sods after treatment with dalapon (2,2-dichloropropionic acid), glyphosate [N-(phosphonomethyl)glycine], or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at varying rates for vegetation control. During establishment, the stands of birdsfoot trefoil were acceptable in all treated- and untreated-sod grass sods except 1 yr in untreated tall fescue (Festuca arundinacea Schreb.) and timothy (Phleum pratensis L.) and 1 yr in tall fescue receiving 3 kg/ha of dalapon. Herbicide treatments resulted in a more rapid development of a significant legume component in the sward and an increase in forage yield over the untreated plots. Minimum herbicide application rates for best return for grass sod control were 0.5, 1, and 5 kg/ha respectively for paraquat, glyphosate, and dalapon.

The persistence of hormone-type herbicides in tissues of susceptible crop plants was studied under growth-chamber and field conditions. The susceptible plants selected were tomatoes (Lycopersicon esculentum Mill.), soybeans [Glycine max (L.) Merr.], and turnips (Brassica rapa L.). Foliage of each species was exposed to herbicides at levels that represented spray drift situations, and the decline of residues was investigated through subsequent chemical analysis. The disappearance of 2,4-D [(2,4-dichlorophenoxy)-acetic acid], 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], mecoprop {2-[(4-chloro-o-tolyl)oxy]propionic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and dicamba (3,6-dichloro-o-anisic acid) was almost linear when concentration data were plotted against the logarithm of time. The results indicate that for practical purposes a kinetic rate equation [conc. = a – b log (time)] would describe the residue decline.

Under unsaturated-flow conditions, bromacil (5-bromo-3-sec-butyl-6-methyluracil) was considerably more mobile than buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxyl-1-methyl-2-imidazolidinone}. Because of their high water solubilities, both herbicides were much more mobile than atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), prometon [2,4-bis (isopropylamino)-6-methoxy-s-triazine], or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. Under saturated-flow conditions, buthidazole was leached through Lakeland loamy sand in slightly greater amounts than tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or CN-10-3510 (formerly VEL 3510) {1-β,β-dimethoxyl-1-methyl-3-[5-(1,1-dimethylethyl)-1,3, 4-thiadiazol-2-yl] urea}. Distribution of the three herbicides in the leached soil was similar and relatively uniform. In Lakeland loamy sand, 30 times as much tebuthiuron was leached under saturated-flow conditions as under unsaturated-flow conditions. Intermittent saturated-unsaturated-flow conditions resulted in four times as much leaching of tebuthiuron as unsaturated flow alone. Only one-tenth as much tebuthiuron leached under intermittent saturated-unsaturated-flow conditions as under saturated-flow conditions. Tebuthiuron added to Lakeland soil and oven-dried was retained in significantly greater amounts than when added to moist Lakeland soil. Low amounts of tebuthiuron leached through Lakeland loamy sand, Portsmouth sandy loam, and Rains silt loam, but high amounts leached through Davidson clay. Greater amounts of the herbicide were retained in the surface zones of the three former soils, but the inverse was the case for the Davidson soil.

Buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl}-4-hydroxyl-1-methyl-2-imidazolidinone} was incubated for 30 days and then leached through Norfolk loamy sand, Lakeland loamy sand, Davidson clay, and Alamance silt loam soils. Similar amounts of the herbicide leached through all of the soils, but distribution in the soils varied greatly. 14C-buthidazole distribution in the Lakeland and Norfolk sandy soils was relatively uniform throughout the soil columns. In the Alamance silt loam and Davidson clay, much greater amounts of buthidazole were found in the upper soil zones than in the lower zones. Six metabolites of buthidazole (dihydroxy, desmethyl dihydroxy, dehydrate, methylurea, urea, and amine) were distributed in varying amounts in each of the soils.

Studies were conducted in North Carolina to determine if johnsongrass [Sorghum halepense (L.) Pers.] rhizomes in the soil exude or produce substances that can affect soybean [Glycine max (L.) Merr.] seedling growth. Fresh and dry weights of soybean seedlings were dependent on the concentration of rhizomes present in the soil before soil samples were used for soybean growth, and on the time of year when soil samples were collected. In studies on rhizome residues, soybean seedling dry weight decreased as percent of dry, decayed rhizomes in the soil increased. For each rhizome concentration, soybean growth inhibition decreased as decay time increased. Fresh and dry weights of soybean plants were reduced by diluted fresh rhizome extract used for irrigation once a week for 3 weeks. Since no rhizomes were present in most of the soils during soybean growth and since nutrient concentrations, organic matter, and pH were not different among the soils used, it is suggested that johnsongrass rhizomes living or decaying in the soil exude, contain, or produce substances that exhibit allelopathic characteristics to soybean growth.

Sand shinnery oak (Quercus havardii Rydb.) was controlled by both picloram (4-amino-3,5,6-trichloropicolinic acid) and tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} in the Rolling Plains vegetational region of Texas. Tebuthiuron provided acceptable control of sand shinnery oak at rates of 0.6 to 1.1 kg/ha, but 2.2 kg/ha of picloram was required to give comparable results. Tebuthiuron pellets applied at 0.6 kg/ha controlled 79% of the sand shinnery oak within 30 to 67 months after application. Applied at 1.1 kg/ha, tebuthiuron controlled 91% (average for three locations). No differences were found between formulations of a given herbicide.

Within 1 yr of collection, 60% or more of false broomweed (Ericameria austrotexana M. C. Johnst.) seed germinated at continuous temperatures from 15 to 30C if light was provided for 8 h daily. Maximum radicle elongation and fresh weight of 14-day-old seedlings occurred at 25 and 30C. Alternating temperatures did not enhance germination, and germination was suppressed in the dark. Germination, time required for germination, and early seedling vigor were tolerant of CaCl2 and MgCl2 solutions at concentrations as high as 200 mM, but NaCl reduced germination at concentrations in excess of 100 mM. Germination was sensitive to polyethylene glycol solution osmotic potentials of 0.6 mPa or more. Reduced germination in salt solutions was attributed to an osmotic effect rather than a direct effect of ions. Other than an inability to germinate when soil water is limited, no narrow environmental requirements appear to restrict establishment of this undesirable rangeland shrub.

Florida beggarweed [Desmodium tortuosum (Sw.) DC] reduced peanut (Arachis hypogaea L. ‘Florunner′) yields more than sicklepod (Cassia obtusifolia L.) when the crop and weeds were allowed to compete for the full season. Regression analyses within years indicated peanut yield reductions of 15.8 to 30.2 kg/ha for each Florida beggarweed per 10 m2 vs. 6.1 to 22.3 kg/ha for each sicklepod per 10 m2. Each kilogram fresh weight per hectare of Florida beggarweed reduced peanut yields 0.15 to 0.74 kg/ha. Reductions in peanut yields ranged from 0.08 to 0.23 kg/ha for each kilogram fresh weight per hectare of sicklepod. Peanut yield reductions correlated more closely with the weights of the weeds than with their populations.

Amine formulations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] and MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} caused a reduction in paraquat (1,1-dimethyl-4,4′-bipyridinium ion) phytotoxicity to barley (Hordeum vulgare L. 'Summit′), wheat (Triticum aestivum L. ‘Neepawa′), and wild oats (Avena fatua L.). Dicamba (3,6-dichloro-o-anisic acid) reduced paraquat activity in barley only. Paraquat phytotoxicity was antagonized more by 2,4-D amine at high than at low rates. Higher rates of paraquat relative to a fixed rate of 2,4-D amine overcame the antagonism. Paraquat phytotoxicity was not antagonized by 2,4-D or MCPA amine applied as a separate treatment. The technical components of the 2,4-D- or MCPA-amine formulations were solely responsible for the antagonism. Ester formulations did not affect paraquat phytotoxicity.

The fate of 3,4-dichloroaniline (DCA), a major metabolite of the herbicide propanil (3′,4′-dichloropropionanilide), in rice (Oryza sativa L.), soil, water, and aquatic organisms was determined in rice-paddy microecosystems. Soil, treated with 10 ppm DCA, was placed in glass chambers, planted to rice, then flooded when the rice reached the two-leaf stage. After flooding, four species of aquatic organisms were added. The concentration of DCA and metabolites in soil, rice, water, and aquatic organisms was determined over a period of time. A maximum of 2.8% of the total radioactivity applied to soil desorbed or leached into water. DCA recovered from water decreased from 12 to 1% of the total radioactivity in water between 1 and 30 days after flooding. Between 10.5 and 18.5% of the radioactivity remaining in soil at the end of the experiments was extractable. Of the radioactivity recovered, between 5 and 11% was DCA, and up to 6 to 19% was 3,3′,4,4′-tetrachloroazobenzene (TCAB), these percentages being dependent on exposure time. Rice accumulated 0.5% or less of the total radioactivity in soil. Only 35 to 55% of the accumulated radioactivity was extractable. Very small amounts of radioactivity were accumulated by aquatic organisms.

The effect of quackgrass [Agropyron repens (L.) Beauv.] density and duration of interference on soybeans [Glycine max (L.) Merr.] was investigated in two studies. In the density study, the average reduction in soybean yield by quackgrass densities of 520 and 910 shoots/m2 was 19 and 55%, respectively. Quackgrass densities of 95 and 160 shoots/m2 did not significantly reduce soybean yields. The number of branches that produced pods, the number of pods and seeds per plant, and soybean height were reduced by the two highest densities. In 1980, quackgrass densities of 265 and 595 shoots/m2 reduced soybean leaf area and plant dry weight. Leaf area partitioning (LAP), leaf weight partitioning (LWP), and net assimilation rate (NAR) of soybeans were reduced by a quackgrass density of 595 shoots/m2. In the duration study, interference by a natural stand of quackgrass for 6 weeks, 8 weeks, and full-season decreased soybean yield an average of 11, 23, and 33%, respectively. Results from the duration study suggest that a selective postemergence herbicide for the control of quackgrass in soybeans would be beneficial if available.

Economical combinations of herbicides and hand labor for weeding sugarbeets (Beta vulgaris L.) in high and low weed densities were determined for irrigated production in the southern Great Plains. Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] preplant incorporated, a 50:50 mixture of phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) and desmedipham (ethyl m-hydroxycarbanilate carbanilate (ester)] sprayed postemergence on small weeds, and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) incorporated at layby controlled pigweed (Amaranthus spp.) and kochia [Kochia scoparia (L.) Schrad.] with acceptable selectivity in sugarbeets. Sucrose yield was identical for all methods of weed control. Using herbicides did not lower, and in some cases doubled, the total cost of weed control in an area with a low weed density. On the other hand, effective herbicide combinations saved $298 to $966/ha compared to total reliance on hand labor in an area with a high weed density. Elaborate combinations of herbicides were not justified even with heavy weed density. The last few weeds remaining in a field can be most economically removed by hand labor.

Little barley (Hordeum pusillum Nutt.) seeds germinated readily without pregermination chilling on substrates moistened with either water or 0.2% aqueous KNO3. Little barley seeds were physiologically mature and viable as early as 11 days after flowering. Pregermination chilling induced dormancy in mature seeds moistened with water, but not those moistened with 0.2% KNO3. Mature seeds frequently germinated better at alternating temperatures from 20C (16 h) to 30C (8 h) than at constant 20C. Germination of seeds after 1 week in a thermogradient table varied from 1% at 34C to 77% at 21C. Seeds were able to germinate over an extended period in the fall and spring. Forage and seed production were highest from the first fall planting date and decreased with later plantings. Plants emerging from seeds planted in March and April did not produce seed.

Adsorption of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] and fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] on a Taloka silt loam (Mollic Albaqualf) and a Roxana silt loam (Typic Udifluvent) from the 10- to 20- and 40- to 50-cm soil depths was measured. The order of adsorption of the herbicides was fluometuron = metolachlor > metribuzin. Adsorptivity of the soil from the 10- to 20-cm depth was greater than from the 40- to 50-cm depth. At 7, 15, 23, and 37C, all herbicides degraded more rapidly as temperature increased. Metribuzin was least persistent and fluometuron and metolachlor were similarly persistent. The time required for the initial herbicide concentration to decrease by 50% in the Taloka silt loam from the 10- to 20-cm depth at 23C was 2.6, 9.4, and 10.1 weeks for metribuzin, fluometuron, and metolachlor, respectively.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] uptake from solution by excised velvetleaf (Abutilon theophrasti Medic.) root segments was studied. Initial atrazine absorption by 1-cm segments cut from the apical 5 cm of roots was rapid. Atrazine concentration in the tissue became equal to the external atrazine concentration by 30 min. Atrazine did not accumulate in the root tissue to concentrations above the external solution, and rapid efflux of atrazine occurred when the root segments were washed with atrazine-free solution. Atrazine absorption was linear over a range of external atrazine concentrations. Dinitrophenol and KCN increased atrazine absorption during the first 3 min of exposure to atrazine. Anoxia increased atrazine absorption but decreased K+ uptake. Decreasing temperatures decreased atrazine absorption. Q10 values for atrazine uptake were between 1.3 and 1.4. The response of atrazine absorption by the excised roots to inhibitors, anoxia, external atrazine concentration, and temperature indicated simple diffusion as the mechanism of absorption of atrazine by velvetleaf roots.

Research involved the behavior of BAS-9052 OH {2[1-(ethoxyimino)butyl]-5-[2(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} in soybean [Glycine max (L.) Merr.] and johnsongrass [Sorghum halepense (L.) Pers.] plants, and the fate of 14C-BAS-9052 OH in intact plants and cell cultures of both species. Microscopic examination of seedling johnsongrass plants (two- to three-leaf stage) treated with foliar applications of 0.48 μg/plant revealed disorganized apical regions and necrotic cells within the apex and leaf primordia of the shoot. Necrotic zones were also evident at the base of expanding leaves and in root apices 1 day after treatment. Following application of 14C-BAS-9052 OH, the same radioactive products were isolated from cell cultures and intact plants. Products included BAS-9052 OH and three unidentified metabolites. Greater proportions of unchanged BAS-9052 OH were extracted from the apical leaves, roots, and cell cultures of johnsongrass than of soybean. BAS-9052 OH was thermal and photo-labile, and a large portion of 14C may not have entered the plant as BAS-9052 OH. However, tolerant soybean plants and cell cultures appeared to have metabolized the herbicide more rapidly than susceptible johnsongrass plants and cell cultures. An average of 64% of the 14C remained in the treated leaf of johnsongrass compared with 48% in soybean. About one-half as much 14C was translocated to the apical leaves of susceptible johnsongrass than tolerant soybean. Therefore, differential uptake and translocation cannot account for the selectivity of BAS-9052 OH.

A method is described to produce inoculum of Alternaria cassiae Jurair and Khan for biocontrol studies. Approximately 8 g of a conidial preparation containing 1 × 108 conidia/g were produced per liter of growth medium. In greenhouse studies the effectiveness of A. cassiae as a biocontrol agent for sicklepod (Cassia obtusifolia L.) was affected by dew-period temperature, dew-period duration, inoculum concentration, and the stage of growth of sicklepod seedlings at the time of inoculation. Optimum environmental conditions included at least 8 h of free moisture at 20 to 30C. Spray mixtures containing approximately 5 × 104 or more conidia/ml gave maximum control when sicklepod seedlings were sprayed to runoff. Sicklepod seedlings in the cotyledon to first-leaf stage were most susceptible to the pathogen.

When buds on the rhizome of quackgrass [Agropyron repens (L.) Beauv.] were released from apical dominance either by increasing the nitrogen supply to the parent shoot (from 5.25 to 210 ppm) or by raising the humidity around the rhizome (from 55 to 100%), the growth response of the buds was closely correlated with their uptake of foliar-applied 14C-labeled glyphosate [N-(phosphonomethyl] glycine]. The 14C level in the buds, expressed on a dry-weight basis, was greatest in the youngest, most rapidly growing bud at the apical node and decreased in successively older buds along the rhizome. A similar gradient was shown by the 14C content of the associated rhizome nodes. The high-humidity treatment also increased the total amount of 14C that was translocated into the rhizome, whereas increasing the nitrogen supply, while promoting 14C uptake by the buds, markedly reduced the amount in the rhizome nodes and in other parts of the plant. This nitrogen-induced reduction in translocation was associated with a reduction of about 30% in uptake of the herbicide by the treated leaves.

Research on biological control of weeds in the United States began early in this century with the use of introduced insects to control the weed, lantana (Lantana camara L.), in Hawaii. The highly successful program for biological control of St. Johnswort (sometimes called “Klamath weed”) (Hypericum perforatum L.) in California by the use of introduced insects in the 1940's and 1950's caused increased interest in this approach to weed control. As a result of this increased interest, the United States Department of Agriculture (USDA) established two overseas laboratories to study arthropod natural enemies of a number of weeds that had been introduced into the United States – in Rome, Italy, in 1959; and near Buenos Aires, Argentina, in 1962. The recent and successful use of an introduced rust pathogen (Puccinia chondrillina Bubak & Syd.) to control rush skeletonweed (Chondrilla juncea L.) in Australia, and the production and utilization of pathogens for control of weeds in the United States, has spurred further interest in biological control.

Aerial applications of pelleted tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N, N′-dimethylurea} at 1 kg/ha to rangeland reduced canopy cover of the subshrub false broomweed (Ericameria austrotexana M.C. Johnst.) by 69 to 78%. Complete control was obtained with 2 kg/ha of tebuthiuron. Picloram (4-amino-3,5,6-trichloropicolinic acid) pellets applied at 2 kg/ha controlled false broomweed in two of four experiments; effectiveness of soil-applied picloram appeared to depend upon sufficient rainfall to move the herbicide into the soil soon after treatment. After the first growing season following application, density of herbaceous species tended to be higher in plots receiving either herbicide than in untreated plots. Picloram suppressed curlymesquite [Hilaria berlangeri (Steud.) Nash], but had little effect on other components of the herbaceous vegetation. Abundance of curlymesquite increased substantially following applications of tebuthiuron, at the expense of annual and short-lived perennial grasses and herbaceous broadleaf species.