The adsorption of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-cholor-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] from aqueous solution by muck soil, and by kaolinite and bentonite saturated with hydrogen or calcium ions, was studied using 14C-labeled herbicides. Both compounds were readily adsorbed from solution by muck soil and Ca- and H-Al-bentonite but only slightly by Ca- and H-Al-kaolinite. Very little of the adsorbed compounds was desorbed after four extractions with distilled water. A bioactivity study using sorghum seedlings (Sorghum bicolor L. ‘RS610′) was conducted with the herbicides in a silica sand medium amended with 1% (w/w) of the various adsorbents. The herbicides were strongly inactivated by muck soil but there was very little inactivation by the clays. There was essentially no movement of either herbicide through 5-cm columns of a silt loam soil and a fine sand soil.

We investigated the toxicity of MSMA (monosodium methanearsonate), fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], and propanil (3′,4′-dichloropropionanilide) to soybeans [Glycine max (L.) Merr. ‘Hill’]. Over-the-top treatments were applied to soybeans at four stages of growth using MSMA at 0.1, 0.2, and 0.4 kg/ha, propanil at 0.2, 0.4, and 0.9 kg/ha, and fluometuron at 0.05, 0.1, and 0.2 kg/ha. Each herbicide caused 10 to 30% soybean injury at the lowest rate, and 40 to 70% injury at the highest rate. Soybeans treated earliest in the growing season usually recovered from injury better than soybeans treated later in the season. Soybean yields were reduced 50 to 70% by MSMA at 0.4 kg/ha and 25 to 35% by propanil at 0.9 kg/ha. Yield losses increased with stage of soybean maturity at time of treatment. Fluometuron at 0.2 kg/ha significantly reduced yield only when applied to soybeans with 7 or 10 trifoliolates or in midbloom.

Seed cotton (Gossypium hirsutum L.) yields were not reduced when competing with prickly sida (Sida spinosa L.) for 7 weeks or less after cotton emergence and maintained weed-free for the remainder of the season. Cotton yields were not affected when pure prickly sida stands were controlled for 5 to 6 weeks after cotton emergence and then allowed to grow uncontrolled for the remainder of the season. In the more severe weed competition treatments, cotton plant height and main stem diameter were reduced; however, yield of seed cotton was the most sensitive indicator of prickly sida competition. Maturity of cotton, as measured by percent of total yield obtained at first picking, indicated a delay in maturity in 1 of 3 yr in treatments where competing prickly sida was present for 8 weeks or more. In density studies, where prickly sida emerged with cotton and was allowed to compete for the full growing season, 45 prickly sida plants/15 m of row caused reductions in yield of seed cotton in two of five experiments. In another series of three experiments as few as 32 prickly sida plants/15 m of row significantly reduced seed cotton yields in two of the three experiments. Trash content of machine-harvested cotton was increased at densities of 64 and 128 prickly sida plants/15 m of row in one experiment. Staple length and grade of cotton were not affected by any weed density studied. Micronaire measurements of cotton were reduced at prickly sida densities of 64 and 128 weeds/15 m of row during 1972.

The site of uptake of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] was studied using a double pot technique. Sorghum [Sorghum bicolor (L.) Moench ‘RS610′] and pea (Pisum sativum L. ‘Alaska’) were the test plants. Herbicidal activity measured by the reduction in fresh weight of the roots and shoots of treated plants showed that exposure of the shoot zone to the herbicides caused much more injury to the plants than root exposure. Translocation of both compounds from root applications to tops of pea and sorghum was studied using 14C-labeled herbicides. There was very little movement of the compounds from the roots of both species. Translocation of the compounds from foliage application was studied using greenbean (Phaseolus vulgaris L. ‘Spartan Arrow’) and soybean [Glycine max (L.) Merr ‘Wayne’]. Almost all of the applied 14C-herbicides remained at the point of application.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 0.14 kg/ha and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one] at 0.56 kg/ha applied under field conditions interacted synergistically to reduce soybean [Glycine max (L.) Merr. ‘Harsoy-63′] growth. In the greenhouse, a number of combinations with atrazine at 0.07 kg/ha or greater and metribuzin at 0.56 kg/ha and greater interacted synergistically to reduce soybean fresh and dry weights 30 days after planting. Over a soil pH range of 4.6, 5.6, and 6.7, atrazine–metribuzin interactions were more apparent as the soil pH values increased. Atrazine at 10-5 and 10-6 M concentration in the sand culture nutrient solution during the early growth of ‘Swift’ soybean seedlings decreased 14C-metribuzin uptake and movement into the 12-day-old soybean shoots during the 12-hr treatment period. However, 10-7 M atrazine increased 14C-metribuzin in the shoot by increasing stomatal aperture and subsequent transpiration. Conditions favoring the synergistic interaction were low atrazine residue levels which increase soybean transpiration, high metribuzin rates, and high soil pH levels.

A sinking leaf-disk technique enabled detection of differences among potato (Solanum tuberosum L.) varieties in herbicide tolerance within 24 hr. Susceptibility of varieties to field application of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5-(4H)-one] was correlated (r = 0.76∗∗) to the number of sunken disks in a metribuzin solution in a growth chamber with continuous light at 30 klux. Varieties that were very tolerant, very susceptible, or intermediate in tolerance to field application of metribuzin were generally in these same categories when evaluated by the sinking leaf-disk technique. Speed of this response was dependent upon herbicide concentration and solution temperature, but the varietal relationships did not change. It was necessary to use leaves of nearly the same age as determined by relative size and position on the plant. Other factors influencing results included plant growth stage, soil moisture, and atmospheric temperature. Results from the sinking leaf-disk test of winter-grown greenhouse plants of the same clones were correlated (r = 0.86∗) to estimated metribuzin injury to field-grown plants. This method, with adequate modification of technique, may have potential use for studying other plant species and other relationships between plants and photosynthesis-inhibiting herbicides.

Greenhouse studies were conducted to study the competition between soybeans [Glycine max (L.) Merr. ‘Vansoy’] and barnyardgrass [Echinochloa crus-galli (L.) Beauv.]. The competition was initiated or terminated when soybeans were 2, 3, 4, 5, 6, 7, 8, 9, and 10 weeks old. The reproductive efficiency of soybeans was not lowered by 4 to 7 weeks of competition after planting of soybeans. Competition between the two species for the entire growing season resulted in a significant decrease in plant height of soybeans. The total dry matter per plant was negatively correlated with an increase in the length of competition. Competition during the first 5 to 9 weeks of the life cycle of soybeans was more deleterious to soybean productivity than the last 5 to 9 weeks of its life cycle.

Yields of cotton (Gossypium hirsutum L. ‘Stoneville 213′) did not differ with various cultivation practices on two soils in Alabama over a 3 to 5-yr period. Cultivation treatments resulted in cotton yields equivalent to but not greater than those resulting from weed removal without soil stirring. However, lack of any weed control resulted in more than 90% yield reduction on Decatur clay loam soil based on a 5-yr average and 95% yield reduction on Hartsells fine sandy loam soil, based on a 3-yr average.

Field experiments were conducted to study the feasibility of applying glyphosate [N-(phosphonomethyl)glycine] postemergence for the control of johnsongrass [Sorghum halepense (L.) Pers.], redroot pigweed (Amaranthus retroflexus L.), and hemp sesbania [Sesbania exaltata (Raf.) Cory] in soybeans [Glycine max (L.) Merr.]. Herbicide sprays were directed across the row to weeds growing taller than soybeans in June, July, and August. Herbicide not sprayed on weeds was trapped and reused. Glyphosate at 1.12 and 1.68 kg/ha effectively controlled johnsongrass with little soybean injury and with greatly increased soybean yields. The use of 0.1% surfactant frequently increased the toxicity of glyphosate at 1.12 and 1.68 kg/ha to soybeans, but this adverse effect was overcome by the use of 0.1% anti-drift polymer in sprays. Control of redroot pigweed with glyphosate at 1.12 kg/ha was improved by the use of 0.1% surfactant, but surfactant did not increase control with glyphosate at 1.68 kg/ha. Glyphosate at 1.68 kg/ha, with 0.1% surfactant, was required to provide more than 80% control of hemp sesbania. Glyphosate applied at 1.12 kg/ha in the recirculating sprayer provided equal johnsongrass control, increased soybean yields and caused less soybean injury than when glyphosate at 0.56 kg/ha was applied over-the-top in water or in foam.

The uptake of naptalam (N-1-naphthylphthalamic acid) by wheat (Triticum vulgare L. ‘Mericopa’) and soybean (Glycine max (L.) Merr. ‘York’) was enhanced when the herbicide was applied simultaneously with SADH (succinic acid-2,2-dimethylhydrazide). Both root and shoot systems of growth regulator-treated plants exhibited enhanced herbicide uptake. Naptalam uptake by wheat seedlings was also stimulated by GA (gibberellic acid), but the GA influence in this respect was less dramatic than that of SADH. The uptake of the herbicide by soybean was not influenced by GA.

Control of annual broadleaf winter weeds in dormant bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] by a variety of herbicides was examined. Nearly all treatments allowed good to excellent control of spur weed (Soliva sessilis P. and K.). Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] was the only tested herbicide that controlled all weed species consistently with a single treatment. Bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide] applied alone as single or repeated treatments controlled spur weed, parsley-piert (Alchemilla microcorpa Boissier Reuter), and chickweed [Stellaria media (L.) Cyrillo], but a combination of bentazon and silvex [2-(2,4,5-trichlorophenoxy)propionic acid] were needed for acceptable control of henbit (Lamium amplexicaule L.) and corn speedwell (Veronica arvensis L.). None of the herbicide treatments affected green-up of bermudagrass the following spring.

Spurred anoda [Anoda cristata (L.) Schlecht.], velvetleaf (Abutilon theophrasti Medic), prickly sida (Sida spinosa L.) and Venice mallow (Hibiscus trionum L.) competition in cotton (Gossypium hirsutum L. ‘Stoneville 213′) was studied during 1973 and 1974. Cotton height was reduced by full-season competition of all species at a density greater than 32 plants/12 m of crop row. Full-season cotton competition reduced the dry matter production of velvetleaf, spurred anoda, prickly sida, and Venice mallow at weed densities less than 8, 16, 32, or 64 plants/12 m of crop row, respectively. Full-season competition resulted in seed cotton yield reductions by spurred anoda, velvetleaf, and prickly sida at 8, 16, and 64, plants/12 m of crop row, respectively. Competition from 2 weeks after cotton emergence until harvest by spurred anoda at 16 plants/12 m, and velvetleaf or prickly sida at 64 plants/12 m, reduced yields. Spurred anoda, velvetleaf, or prickly sida competition 4 to 6 weeks after cotton emergence until harvest did not reduce the seed cotton yields. Venice mallow competition did not reduce yields at any density or competition period.

The movement of dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), and 2,4-D [(2,4-dichlorophenoxy)acetic acid] was studied in five Canadian prairie soils using soil columns. The three acid herbicides showed the following general order of decreasing mobility in the five soils: Asquith sandy loam > Indian Head loam > Regina heavy clay > Weyburn Oxbow loam > Melfort loam, thus indicating an inverse relationship between adsorption and mobility. In general, the distribution coefficients (kd) were comparable to the corresponding Freundlich constants (k) and these were significantly related to the soil organic matter content, to a lesser extent to soil pH, and not correlated with soil clay content. The maximum concentrations of all three herbicides in the column effluents were well below their respective water solubilities and were inversely related to the distribution coefficients. The calculated values for the amounts of precipitation required to leach the three herbicides to a depth of 10 cm showed the following order of mobility: dicamba > picloram > 2,4-D.

Purple moonflower's (Ipomoea turbinata Lagasca y Segura) vegetative growth and seed maturation were characterized in noncompetitive field studies. Seedling emergence of 50% or greater of mature scarified seed occurred to a soil depth of 12 cm. At vegetative maturity a typical plant produced 11 primary, 50 secondary, 94 tertiary, and 7 quaternary runners having a total length of 185 m. The average number of leaves per plant was 1,120. Maximum seed size, seed wet weight, occurrence of first mottled seed, and first capacity to germinate occurred 20 days after anthesis in immature seed that were removed from the seed pod. Maximum germination occurred at 26 days after anthesis. Seed moisture content (dry weight basis) reached 8.5%, seed had formed an impermeable seed coat, and physiological maturity (defined as maximum dry weight) occurred 34 days after anthesis. The total number of purple moonflower seed produced per plant averaged 9350. The major mechanism of seed dormancy was impermeability of seed coats.

Weed-free sugarbeets [Beta vulgaris (L.) Beauv.] growing at a spacing of 60 cm (1/2 stand) yielded the same weight of roots as those spaced 30 cm (full stand), and those spaced 90 cm (1/3 stand) yielded about 90% as much. Gross sucrose yield was reduced somewhat more, because the larger roots growing in partial stands contained a lower percentage of sucrose than the roots in full stands. Annual weeds that emerged after July 1 were suppressed and. killed by competition from sugarbeets of normal vigor in a full stand, but became competitive when the sugarbeets were spaced at 1/2 or 1/3 of a full stand. Competition from barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and pigweed (mixture of Amaranthus retroflexus L. and A. powellii S. Wats.), which reached a height of 150 cm, reduced root yields 5 to 39% in 1/2 stands and 19 to 49% in 1/3 stands, as compared with weed-free sugarbeets in the same stands. Hairy nightshade (Solarium sarachoides Sendt.) was abundant but never became taller than the sugarbeets. Its competition had no measurable effect on the sugarbeets.

Establishment and early growth characteristics were defined for sourgrass [Trichachne insularis (L.) Nees], one of the most serious pasture weeds in Hawaii. Optimum germination of sourgrass seeds was obtained in the light at 30 C or with alternating temperatures of 20 and 30 C or 25 and 35 C. Germination in complete darkness was poor except at alternating 25 and 35 C. Sourgrass germinated better than buffelgrass (Cenchrus ciliaris L.) and guineagrass (Panicum maximum Jacq.) at low moisture tension. Sourgrass was capable of emerging from a maximum depth of 5 cm but percent emergence was greatly reduced at planting depths greater than 3 cm. Sourgrass flowering response to photoperiod was day-neutral. Under conditions of adequate moisture, the growth of sourgrass was severely suppressed when grown with buffelgrass, or/or guineagrass. If grazing is restricted, either of these grasses would be useful for controlling sourgrass.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide] mixed with plaster-of-paris in concentrations of 0.5, 1, 2, and 4% (w/w) was cast into tablets of three sizes. The controlled release of the herbicide was tested by the following methods: (a) in the laboratory with eduction by soaking tablets in water, (b) in the greenhouse with azalea (Rhododendron obtuseum Planch. ‘Richardii’) stock in container, and (c) in the lathe house with azalea stock in containers. In the laboratory experiment, the quantity of herbicide educed from tablets of equivalent volumes, weights, and concentrations were similar regardless of surface area of the three tablet sizes. Successively decreasing quantitites of alachlor were educed with each of the first 10 soakings. Following these soakings, the quantity of alachlor educed per soaking stabilized for the next 30 soakings. In both greenhouse and lathe house experiments, azalea plants treated with as much as 45 kg/ha alachlor formulated in tablet(s) were not damaged. In the best greenhouse treatments, two small tablets per container, effective weed control was obtained for up to 7.5 months from a single application of alachlor at rates of 11, 22, and 45 kg/ha.

UHF energy (2450 MHz) was applied to seeds and seed-soil mixtures with a waveguide under controlled conditions. After treatment, seeds were germinated at 27 C to determine viability. Seeds were either killed or seedlings grew normally with no intermediate levels of inhibition typical of that produced with sub-lethal dosages of herbicides. The energy required to kill several species of dry seeds ranged from 88 to 183 J/cm2 and could be reduced 12 to 42% by a 24-hr imbibition period prior to treatment. When several seed-soil mixtures were treated, the greatest toxicity occurred in a moist muck and clay loam soil, with the least toxicity on a dry loamy sand soil. Although attenuation of activity occurred in dry soils of three types, less energy was required to kill seeds in moist soils than was required in the absence of soil. Increasing the power levels reduced the time of exposure necessary to kill barnyardgrass [Echinochloa crus-galli (L.) Beauv.] seeds. Less energy was required to kill seeds as the soil temperature was increased from −20 to +18 C.