Absorption and translocation of the sodium salt of radioactive (2,4-dichlorophenoxy)acetic acid (2,4-D-2-14C) by wolftail (Carex cherokeensis Schwein) plants grown from rhizomes were enhanced by high relative humidity but were not affected by dimethyl sulfoxide (hereinafter referred to as DMSO). Greatest accumulation of 2,4-D-2-14C translocated from the treated leaf occurred, in the meristematic tissue. DMSO increased the herbicidal activity of the triethanolamine salt of 2,4-D alone, but 2,4-D plus DMSO was no more effective than 2,4-D plus X-77. When both DMSO and X-77 were added to the 2,4-D solution, the treatments were no more effective than when either additive alone was included.

Peanut (Arachis hypogaea L.) yields were not influenced by weeds that were removed within 3 weeks after planting and each week thereafter, but a yield reduction did occur when weeds were not removed until 4 to 8 weeks after planting. Peanuts kept weed free at least 6 weeks after planting showed no yield loss due to competition from weeds emerging later. As weed competition increases, peanut seed yield, forage yield, and soil moisture content decreases.

The etymology of herbicide has been traced to a U. S. trademark originally registered by William J. Reade of the Reade Manufacturing Company.

With a corn (Zea mays L.) yield of 144 bu/A on weed-free plots, giant foxtail (Setaria faberii Herrm.) reduced corn yields 1, 2, 5, 7, and 18 bu/A, respectively, when removed when 3, 6, 9, and 12 inches high and at maturity. With a soybean (Glycine max L.) yield of 30 bu/A on weed-free plots, the same treatments reduced soybean yields 0, 0, 1, 2, and 18 bu/A, respectively. Giant foxtail competing with corn delayed tassel emergence but had little effect on moisture of grain or on shelling percent at harvest. The total dry matter produced per acre remained relatively constant whether the dry matter was made up of corn alone or corn and weeds. The greatest competitive effect of giant foxtail with soybeans occurred after the reproductive stage of soybeans began or after the weeds became sufficiently dense to reduce the light which soybeans received. Early-season competition had greater effect on corn than on soybeans. However, the taller growing corn competed better than soybeans with giant foxtail later in the season.

Four greenhouse trials were conducted to determine the effects of various growth temperatures and soil moistures on dormancy of primary seed of selected strains from two wild oat (Avena fatua L. ssp. fatua (L.) Thell.) varieties. Both higher temperature and lower level of moisture decreased dormancy, temperature having a greater effect than level of soil moisture. The dormancy difference between seed produced on plants grown at 15.6 to 18.3 C in soil with approximately 75% or from 100 to 75% available moisture and at 25.3 to 28.4 C in soil with approximately 25% or from 100 to 25% available moisture ranged between 31 and 100%, dormancy tests being conducted 10 or 14 days after seed maturity. The magnitude of the difference in seed dormancy caused by conditions of growth was affected by strain and variety of wild oat, and by age of seed.

A 2-year field study was conducted to determine the effects of periodic removal of topgrowth on tuber production and persistence of sago pondweed (Potamogeton pectinatus L.) in an irrigation canal. Plots were treated at 1, 2, and 4-week intervals throughout the irrigation season with aromatic solvent to kill the topgrowth. The tuber population was determined before the treatments began and at the end of each season. At the end of the first season, the number of tubers was reduced 78, 87, and 54% in the plots treated at 1, 2, and 4-week intervals, respectively. After two seasons, the number of tubers was reduced 91, 81, and 80%, respectively. All treatments controlled sago pondweed topgrowth effectively, but none eliminated the tubers completely.

The phytotoxicity of N,N-dimethyl-2,2-diphenylacetamide [diphenamid], N-methyl-2,2-diphenylacetamide, 2,2-diphenylacetamide, and 2,2-diphenylacetic acid was studied on tomatoes [Lycopersicon esculentum Mill.], common lambsquarters [Chenopodium album L.], redroot pigweed [Amaranthus retroflexus L.], and rape [Brassica napus L.], by means of nutrient solution culture techniques. Diphenamid was the most phytotoxic; 2,2-diphenylacetic acid was the least active. Only minor differences in the arithmetical means of the phytotoxicity indices existed in the phytotoxicity of the N-methyl and amide analogs of diphenamid.

Dissipation of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) was greater in Sharpsburg silty clay loam soil than in Anselmo sandy loam soil and was faster in the topsoil than in the subsoil. Breakdown increased with increasing soil incubation temperatures. Phytotoxicity of dicamba and 3-amino-2,5-dichlorobenzoic acid (amiben) in aqueous solutions decreased upon exposure to sunlight. Amiben was more susceptible to photodecomposition than was dicamba. Aqueous dicamba solutions exposed to sunlight for 16 days decreased growth of cucumber (Cucumis sativus L.) seedlings, while amiben solutions caused no growth reduction after 2 days' sunlight exposure. Dicamba solutions exposed to 60 C showed increased phytotoxicity while amiben solutions were unaffected. Dicamba was most phytotoxic to corn (Zea mays L.) seedlings at pH 4 and to cucumber seedlings at pH 5. Dicamba solutions were taken up by both shoots and roots of corn and cucumber seedlings; however, root uptake resulted in greater growth reductions.

Experiments were conducted at Crawford and Kimball, Nebraska, during 1962, 1963, 1964, and 1965 to determine the effect of 13 herbicides on plains pricklypear (Opuntia polyacantha Haw.). The best control was obtained with 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), 4-amino-3,5,6-trichloropicolinic acid (picloram), 3,6-dichloro-o-anisic acid (dicamba), and (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T). Silvex and picloram were superior to dicamba and 2,4,5-T in controlling plains pricklypear, but picloram and dicamba injured the native grasses. Rotary hoeing plains pricklypear cladodes just prior to spraying improved herbicide performance. Simulated railing was not a consistent control measure. Evaluation of plains pricklypear control was made 1 and 2 years after herbicide application.

Grain sorghum (Sorghum vulgare Pers.) was sprayed in 1966 and 1967 with 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), propylene glycol butyl ether ester of 2,4-dichlorophenoxyacetic acid (2,4-D), alkanolamine salts of 2,4-D, and nonphytotoxic petroleum oil (crop oil) or their combinations when plant heights were 2 to 4, 4 to 6, and 6 to 8 inches for grass weeds, broadleaf weeds, and sorghum, respectively. Pollen mother cells from all herbicide-treated sorghum revealed chromosomal aberrations, mostly aneuploidy and polyploidy, and aberration frequencies increased when herbicides were combined. Added chromosomes were not always of the basic number. Atrazine-treated plots produced highest grain yields, kernel numbers were reflected in grain yield (r = .96), and untreated plants flowered first.

Several herbicides and herbicide combinations were investigated for desiccation, defoliation, and killing of tropical vegetation near Mayaguez, Puerto Rico. Hydroxydimethylarsine oxide (cacodylic acid) was one of the more effective defoliants on guava (Psidium guajava L.) within 2 weeks after treatment. However, several herbicide combinations including contact: growth-regulator types were more effective 1 month after spraying. Six months after treatment, herbicides containing (2,4-dichlorophenoxy)-acetic acid (2,4-D), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), or 4-amino-3,5,6-trichloropicolinic acid (picloram) were superior to contact herbicides in controlling regrowth. In a mixed tropical forest, most rapid desiccation and defoliation of vegetation was produced by 6,7-dihydrodipyrido (1,2-a:2′,1′c) pyrazinediium salt (diquat) within 2 weeks after treatment. At 1 month after treatment and longer, the 1:1 mixture of the butyl ester of 2,4-D:2,4,5-T and a 2:2:1 mixture of the isooctyl esters of 2,4-D:2,4,5-T:picloram were superior to other herbicides.

Field plots of small well-rooted plants of yew [Taxus media Rehd., var. Hicks] and maple [Acer palmatum Thunb., var. Japanese maple] were treated annually for 3 years with 3-(3,4-dichlorophenyl)-1,1-dimethylurea [diuron], 2-chloro-4,6-bis(ethylamino)-s-triazine [simazine], 2-(2,4-dichlorophenoxy)ethyl sodium sulfate [sesone], dimethyl tetrachloroterephthalate [DCPA], isopropyl m-chlorocarbanilate [chlorpropham], α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine [trifluralin], 2-sec-butyl-4,6-dinitrophenol [dinoseb], and 3-amino-s-triazole [amitrole]. Commercial formulations of the herbicides were applied in water as a soil drench in May each year, at minimum effective dosage levels for weed control and at much higher levels. Diuron at herbicidally effective rates significantly reduced stand and growth of yew and maple plants. Simazine and sesone caused noticeable but variable reductions in growth of maple plants that were not statistically significant and yew plants were unaffected by these treatments. None of the other herbicides caused visible or measurable differences in growth.

Imbibed seeds of rough cinquefoil (Potentilla norvegica L.) remain dormant in darkness at constant and alternating temperatures. Full promotion of germination resulted after 3 days' dark imbibition at 25 C followed by 24 hr of continuous unfiltered fluorescent light. Germination was controlled by phytochrome. The sensitivity of the seeds to short light exposures was increased by the introduction of a temperature shift to 40 C for 2 hr, at the conclusion of the normal dark imbibition period at 25 C. The temperature shift also reduced the time required in continuous light to give full promotion of germination. The response to light was synergistically increased when the seeds were imbibed in 0.2% KNO3, and given the temperature shift. Nearly full promotion was reached with ca. 5 min of red light, and 50% germination occurred with as little as 1 sec. The system was still under phytochrome control. These findings suggest a mechanism by which soil populations of weed seeds may become physiologically conditioned to respond to very brief exposures to light.

Field screening methods were developed which proved very reliable in accurately assessing the potential of herbicides during the first year of testing. Under conditions imposed by these methods, the herbicides usually exhibited maximum toxicity, thereby indicating which ones might be potentially hazardous in growers' fields when crop tolerance is lowered by adverse growing conditions. Of the 29 crop uses suggested by the data, 16 are registered by the USDA and are now in current use. Of these 29, 26 were indicated during the first year of testing and substantiated by data from an additional 1 to 4 years of testing.

Common Kentucky bluegrass (Poa pratensis L.) sod-plugs were grown in the greenhouse in soil freshly treated with 11 herbicides and in soil collected from the 0 to 2 and 2 to 4-inch depths of field plots treated 10 months earlier with the same herbicides. Fresh herbicide treatments reduced significantly the root regrowth of the bluegrass plants. The 12-lb/A rate of the fresh application of 1-(2-methylcyclohexyl)-3-phenylurea (siduron) caused the least chemical inhibition of root regrowth. The most phytotoxic fresh applications were 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), both killing the bluegrass plants at the 4 lb /A rate. Root regrowth of bluegrass grown in the herbicide residue samples was significantly reduced for all treatments. Herbicides which tended to persist in the 0 to 2-inch soil level and were most phytotoxic to root regrowth were simazine, polychlorodicyclopentadiene isomers (hereinafter referred to as bandane), N-(2-mercaptoethyl)-benzenesulfonamide S-(O,O-diisopropyl phosphorodithioate) (bensulide), and 2,6-di-tert-butyl-p-tolyl-methylcarbamate (terbutol). Those herbicides which tended to leach into the 2 to 4-inch soil level and cause the greatest reduction of root regrowth were N-butyl-N-ethyl-alpha, alpha, alpha-trifluoro-2,6-dinitro-p-toluidine (benefin), α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), atrazine, and O-(2,4-dichlorophenyl) O-methyl isopropylphosphoramidothioate (DMPA). Herbicides which tended to leach uniformly throughout the 0 to 2 and 2 to 4-inch soil layers were siduron, an equal mixture of 1,1-dimethyl-4,6-diisopropyl-5-indanyl ethyl ketone and 1,1-dimethyl-4,6-diisopropyl-7-indanyl ethyl ketone (hereinafter referred to as sin-done), and dimethyl 2,3,5,6-tetra-chloroterephthalate (DCPA).

During 1967, field studies on the Holston River and in the laboratory produced evidence that excessive aquatic plant growths are not soley related to the presence of large amounts of nutrients in water. Factors contributing to growth were the amount of nutrients in sediments, water depth, and turbidity. Water depth and turbidity influence the amount of light which penetrates the water and is available for the growth of rooted plants.

The adsorption of seven s-triazines from aqueous solutions by organic soil colloids was determined at pH levels from 1.0 to 5.2. Maximum adsorption occurred at pH levels in the vicinity of the pKA values of the respective compounds. The amounts adsorbed were dependent upon the molecular structures of the compounds and the pH of the suspension and were, in order of decreasing adsorption, as follows: 2-methoxy-4,6-bis(diethylamino)-s-triazine (hereafter referred to as tetraetatone) = 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) = 2-hydroxy-4,6-bis(isopropylamino)-s-triazine (hereafter referred to as hydroxypropazine) > 2-methoxy-4-diethylamino-6-ethylamino-s-triazine (hereafter referred to as trietatone) > 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone) > 2-methoxy-4,6-bis(ethylamino-s-triazine (simetone) > 2-chloro-4,6-bis(isopropylamino-s-triazine (propazine). Approximately 52% of the prometone adsorbed by the organic matter was desorbed with two extractions of 0.1N NaCl. It was concluded that the adsorption of the s-triazines was due to complexing of the triazine molecules with functional groups on the organic colloids and/or adsorption of s-triazine cations by ion exchange forces.

Whitebrush (Aloysia lycioides Cham.) near Llano and Marble Falls, Texas was treated at 19 dates with broadcast applications of the potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) as the 2% granules. At Llano, the average percentages of whitebrush plants killed with 1, 2, and 4 lb/A rates of picloram granules at five dates were 18, 52, and 87; however, at three dates, the 3 lb/A treatment killed 98% of the plants. Picloram granules were applied at 15 dates at Marble Falls where 1, 2, 3, and 4 lb/A rates averaged 17, 43, 68, and 79% of the whitebrush plants killed, respectively. Picloram was most toxic when applied during the cooler months, particularly when application was soon followed by rains. Broadcast sprays of the potassium salt of picloram were included at two dates and were more effective than granules. Most individual whitebrush plants were killed by one-third tablespoon of the 10% granule, or by 2 tablespoons of the 2% granule of picloram applied in an area 2 ft in diam at the base of the stem.

The relative adsorption and migration of four thiocarbamate herbicides were studied in five soil types. Pebulate (S-propylbutylethylthiocarbamate) was adsorbed to the greatest degree by any one of the soils or adsorbents used. EPTC (ethyl N-N-dipropylthiocarbamate) showed the least adsorption while ethyl N-ethyl-N-cyclohexylthiocarbamate (hereinafter referred to as R-2063) was intermediate. Charcoal and bentonite clay were very effective adsorbents while the soils varied in their ability to adsorb the herbicides. A correlation was found between the rate of adsorption and the amount of organic matter in the soil. Such correlation was not found with the clay content, but a multiple regression test showed that the clay content is also closely associated with adsorption. The leaching of EPTC, pebulate, R-2063, and S-2,3-dichloroallyl N,N-diisopropylthiolcarbamate (diallate) in soil columns was directly related to their solubilities in water and inversely related to the organic matter content of the soil. Incorporation of the herbicides into the upper 5 cm of the soil did not alter the pattern or depth of their leaching. The lateral diffusion of thiocarbamates in the soil was much more restricted than the leaching downward. Again, this movement was closely related to the water solubilities of the herbicides, to soil organic matter, and apparently to the vapor pressures of the herbicides. EPTC vapor loss was the greatest followed in order by pebulate and R-2063. The rate of vapor loss from soils of all of the herbicides tested was reduced when the soil properties enabled rapid infiltration and drying of the spray drops.

A root bioassay was used to compare the adsorption of herbicides by activated carbon with that of muck soil, bentonite clay, a cation exchange resin, and an anion exchange resin. The effectiveness of different adsorbents was determined by comparing the concentrations of herbicide required to give 50% root inhibition of the test plant. Of eight herbicides tested, six were more strongly adsorbed by activated carbon than by any of the other adsorbents. The relative amount of adsorption by activated carbon as measured by the reduction in biological activity was as follows: isopropyl N-(3-chlorophenyl)-carbamate (CIPC) > α,α,α,trifluro-2,6-dinitro-N, N-dipropyl-p-toluidine (trifluralin) > 2,4-dichlorophenoxyacetic acid (2,4-D) > N,N-dimethyl-2,2-diphenylacetamide (diphenamid) > dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) > 4,6-dinitro-o-sec-butylphenol (DNBP) > 3-amino-2,5-dichlorobenzoic acid (amiben). The biological activity of 1,1'-dimethyl-4,4'-bipyridinium salt (paraquat), a cationic herbicide, was not reduced by activated carbon, but was reduced by bentonite clay and the cation exchange resin. DNBP was more strongly adsorbed by the anion exchange resin than by activated carbon. Desorption from activated carbon varied greatly for the herbicides tested. The most readily desorbed herbicide was 2,4-D while CIPC and DNBP showed little or no desorption.