The allelopathic potential of leafy spurge (Euphorbia esula L.) was investigated in the field and greenhouse. Reductions in frequency and density of quackgrass [Agropyron repens (L.) Beauv.] and common ragweed (Ambrosia artemisiifolia L.) were noted where leafy spurge had high densities in the field. Field soil samples taken from areas of moderate and high leafy spurge densities inhibited tomatoes (Lycopersicon esculentum Mill.) in the greenhouse. Growth of seedlings was inhibited up to 60% when leafy spurge leaves, roots, or litter were incorporated into soil, but surface applied leafy spurge litter had no effect. Growth inhibition was demonstrated for crabgrass [Digitaria sanguinalis (L.) Scop.] and tomato when 0.1 to 1.0% (w/w) of leafy spurge leaves or roots were added to soil. Based on these studies we postulate that leafy spurge exhibits allelopathic characteristics which may result from the incorporation of dead or decaying plant material in soil.

The effects of short exposures to low temperature on cotton (Gossypium hirsutum L. ‘Stoneville 213′), velvetleaf (Abutilon theophrasti Medic), and spurred anoda [Anoda cristata (L.) Schlecht.] were studied in controlled environment chambers. A 3-day exposure to 17/13 C day/night temperatures 24 days after planting significantly reduced dry weight, leaf area and height in all three species when compared to control plants maintained at 26/21 C day/night. After subsequent periods of 7 days at 26/21 C and 8 days at 29/23 C, the two weed species recovered in growth more completely than did cotton. Therefore, the weed/crop ratios for dry weight and leaf area were increased by the imposition of the cold treatment. Mathematical analysis of the growth of the three species indicated that the growth reductions during the cold treatment were caused by decreases in both net assimilation rate and leaf area duration. The net photosynthetic rates and stomatal conductances of individual leaves of cotton and velvetleaf were significantly reduced during the cold treatment but recovered to control levels during a subsequent 4-day exposure to 26/21 C. We conclude that the adverse effects of low temperatures on the growth of cotton, velvetleaf, and spurred anoda are caused mainly by reductions in leaf area production. Because of its slower and less complete recovery, cotton is more severely affected by low temperature than either of the two weeds. Our results help explain the observation that velvetleaf and spurred anoda are more competitive with cotton following abnormally cool periods early in the growing season.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied as a preplant treatment at rates of 2.24 to 8.96 kg/ha was evaluated for the control of perennial grasses and the establishment of jeffrey (Pinus jeffreyi Grev. & Balf.) and ponderosa (Pinus ponderosa Laws.) pine transplants. The most consistent and effective rates of atrazine (6.72 and 8.96 kg/ha) reduced grass herbage biomass an average of 72% over a 3-yr period and increased average final survival of transplants from 1% on the control to 66% with treatment. These rates also gave continued grass control for at least 3 to 4 yr after treatment. Stem diameter and top growth tended to be greater on the most effective treatments. High survival and increased growth of transplants on these treatments were attributed to low soil moisture tensions and increased NO3-N accumulation throughout the summer to depths of 30 cm during the year of planting and subsequent years.

The effects of five preemergence herbicides on turfgrass quality and control of crabgrass (Digitaria spp.) were measured to determine the influence of thatch on preemergence herbicide activity in Kentucky bluegrass (Poa pratensis L.) turf. Field applications of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin -5-one], and prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} to thatchy Kentucky bluegrass turf in spring caused injury that was apparent during periods of summer stress, while DCPA (dimethyl tetrachloroterephthalate) and bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] caused little or no injury. The same treatments on thatch-free sites revealed that only prosulfalin was injurious. Adsorption of benefin, bensulide, and DCPA from solution was greater by thatch than by soil; however, the mobility of these herbicides in undisturbed thatch profiles was greater than measured in undisturbed surface soil from thatch-free sites. Thus, turfgrass injury from preemergence herbicides on thatchy sites is due to at least two factors: the greater mobility of preemergence herbicides in thatch than in soil; and the inherent susceptibility of Kentucky bluegrass to injury from preemergence herbicides that come into direct contact with roots and other absorbing organs.

Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4 (1H, 3H)-dione] effectively controlled herbaceous weeds in a loblolly pine (Pinus taeda L.) plantation in 1975. Pine seedling height increased as a result of weed control following 1 to 3 kg/ha applications but phytotoxic symptoms were evident. A 1976 field study indicated activated charcoal root coatings may reduce phytotoxic action. Hexazinone at 3 and 4 kg/ha applied to either the foliage or the soil was toxic to potted pine seedlings in 1976. The addition of surfactant to hexazinone treatments at 2, 3, and 4 kg/ha increased pine phytotoxicity to unacceptable levels. When hexazinone was applied to soil at 2, 3, and 4 kg/ha, activated charcoal root coatings reduced pine mortality to acceptable levels on Norfolk sandy loam. Charcoal was less effective on Madison clay loam. Pine tolerance on both soils was acceptable at 2 kg/ha.

The adsorption of picloram (4-amino-3,5,6-trichloropicolinic acid) was determined on an Aiken silt loam, on three cation exchange resins and on a single anion exchange resin. Adsorption data were evaluated using parameters in the Freundlich equation and their dependance upon cationic composition of the exchange complex, the ionic composition of the equilibrium solution, and the equilibrium solution pH. For the Aiken soil saturated with metallic cations the order of decreasing picloram adsorptive capacity was Fe+3 = Cu+2 > Al+3 > Zn+2 > Ca+2 > native soil. Increases in adsorption compared to the native Aiken soil could be explained on the basis of decreases in the equilibrium solution pH except for Fe+3, Zn+2, and especially the Cu+2 treatments. The adsorptive capacity of the Aiken soil was altered by the addition of several salts simulating addition of fertilizer salts. The Cu+2 and Zn+2 salts were the only treatments showing increased adsorption which could not be explained readily by pH changes. KH2PO4 and NH2CONH2 (urea) reduced picloram adsorption. Dowex 50-1 × 4, a strongly acidic cation exchange resin, showed increased picloram adsorptive capacity in the order Cu+2 > Al+3 > Ca+2 > Zn+2 = H+. Cellex CM, a weakly acidic cellulose exchanger had increased adsorptive capacities in the order of Cu+2 > Ca+2 > Al+3 > Na+ > Fe+3 > Zn+2. Picloram adsorption by an anion exchange resin at pH 6.1 was nearly 100%. These results suggest that complex formation of picloram with polyvalent cations on the exchange complex is likely especially for Cu+2 and to a lesser extent Fe+3 and Zn+2. In soils such complex reactions would most probably involve organic matter, polyvalent cations, and picloram. The formation of chelate ring species is proposed.

The feasibility of herbicide and crop rotation for the control of johnsongrass [Sorghum halepense (L.) Pers.] in corn (Zea mays L.) was studied in field experiments. Light infestations of johnsongrass were initially present, but it became the predominant weed after 4 yr of continuous corn treated with atrazine [2-chloro-4-(ethylamino)-6-(isopropylamine)-s-triazine], cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl]amino]-2-methylpropionitrile}, and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], alone and in combinations at rates of 2.24, 2.24, and 0.84 kg/ha, respectively. The infestation of johnsongrass was effectively controlled by growing corn in rotation with cotton (Gossypium hirsutum L.) in a cropping sequence of corn-cotton-cotton-corn, in which trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] and MSMA (monosodium methanearsonate) at 0.56, 2.24, and 2.24 kg/ha respectively, were used for weed control in cotton. In the corn-cotton-cotton-corn cropping sequence, the herbicide treatments also prevented increases in the populations of other indigeneous weeds including prickly sida (Sida spinosa L.), prostrate spurge (Euphorbia supina Raf.), spotted spurge (Euphorbia maculata L.), common purslane (Portulaca oleracea L.), tall morningglory [Ipomoea purpurea (L.) Roth], common cocklebur (Xanthium pensylvanicum Wallr.), spurred anoda [Anoda cristata (L.) Schlecht.], hemp sesbania [Sesbania exaltata (Raf.) Cory], redroot pigweed (Amaranthus retroflexus L.), goosegrass [Eleusine indica (L.) Gaertn.], junglerice [Echinochloa colonum (L.) Link], large crabgrass [Digitaria sanguinalis (L.) Scop.], and purple nutsedge (Cyperus rotundus L.).

Aerial sprays of asulam (methyl sulfanilylcarbamate) applied at 3.4 or 6.7 kg/ha to forest plantations in western Oregon effectively controlled western bracken [Pteridium aquilinum (L.) Kuhn var. pubescens Underw.] without damaging Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings. Asulam also did not damage noble fir (Abies procera Rehd.) seedlings if applied without a surfactant. The half-life of asulam in forest soils ranged from less than 7 to 18 days and vertical movement in the soil profile was minimal. No herbicide residues were found in runoff water from treated areas up to 208 days after application.

Sixteen soybean [Glycine max (L.) Merr.] cultivars were evaluated for their response to the rice herbicide propanil (3′,4′,-dichloropropionanilide) applied at two growth stages. Application of 3.4 kg/ha resulted in more injury than 0.6 kg/ha. Application at the stage of growth when three nodes on the main stem had completely unrolled leaves (V3) resulted in more injury than when eight nodes had completely unrolled leaves (V8). As determined by seed yield when treated at 3.4 kg/ha propanil at the V3 stage of growth, ‘Pickett 71′, ‘McNair 600′, ‘Tracy’, and ‘Bragg’ were the most tolerant; ‘Hutton’, ‘Hampton 266A’, ‘Bossier’, ‘Ts 74-34′, ‘Semmes', and ‘Forrest’ were moderately sensitive and Dowling’, ‘Davis', ‘Mack’, ‘Dare’, ‘Ranson’, and ‘McNair 800’ were the most sensitive to propanil injury.

Optimum germination of Canada thistle [Cirsium arvense (L.) Scop.] occurred at alternating temperatures of 20 to 30 C and 30 to 40 C and at a constant temperature of 30 C. Osmotic pressures of 7 bars and greater reduced germination, but 2% of the seeds germinated at 15 bars. Canada thistle seeds (14%) were able to germinate in NaCl concentrations of 20,000 ppmw. Light was important in seed germination, however, its effect could be overcome by adding GA3 (gibberellic acid) to the germination medium. Optimum pH for germination was between 5.8 and 7.0. Depth of planting influenced emergence; the highest percentage of seedlings emerged from depths of 0.5 to 1.5 cm. Canada thistle seedlings tolerated average soil moisture tensions of 1.3 bars and continued to grow. Canada thistle seedlings 19 days old and with two true leaves were able to resprout after top-growth removal. Regrowth was evident on 8% of the clipped plants 4 days after initial top-growth removal.

Showy crotalaria (Crotalaria spectabilis Roth) seed dormancy was due to seed coat impermeability to water. The seed coats became impermeable during later stages of maturation on the plant. When incubated immediately after harvest, 9% of the mature, black seeds (11% water content) imbibed water and germinated. The remaining 91% had impermeable coats and did not germinate. After dry storage for 3 months at 23 C, 24% of the seeds imbibed water and germinated. Seeds of another seed lot, which contained seeds of different maturity stages, attained 47% imbibition and germination after storage for 1 yr. The dry, less mature green seeds had a higher percentage (51%) of permeable seeds than did the black seeds (31%) from the same lot. Several seed coat treatments induced imbibition of water and germination of previously impermeable seeds. Effective treatments included piercing of seed coats, scarification with sandpaper, soaking in 70 C water, and simply applying pressure on the strophiole area. Covering the pressed strophiole with petroleum jelly significantly blocked imbibition and indicated that water entered the seeds at only the pressed area. However, studies indicated natural loss of impermeability in showy crotalaria seeds may occur at other sites as well.

We studied the effects of temperature (5, 10, 20, and 30 C) on the phytotoxic activity of decaying quackgrass [Agropyron repens (L.) Beauv.] leaves and rhizomes that were incubated in soils for 0, 1, 2, 4, and 6 weeks. Alfalfa (Medicago sativa L.) seeds were grown for 96 h in water, water extracts of control soils, and water extracts of soil with quackgrass rhizomes or leaves. Dried quackgrass rhizomes and leaves contained water-soluble toxins that inhibited alfalfa seedling development and growth. There was a strong interaction between incubation time and temperature on the development of additional toxins by decomposing quackgrass. High incubation temperature (30 C) accelerated toxin formation and ultimate decay. Intermediate temperature (20 C) delayed toxin formation and decay. Low incubation temperatures (5 C and 10 C) prevented formation of additional toxin. In all extracts of quackgrass and soil that had been incubated for 6 weeks, normal alfalfa seedling number equaled that in water. However, seedling growth varied with incubation temperatures.

Treatment of quackgrass with glyphosate [N-(phosphonomethyl) glycine] in the greenhouse did not influence the toxicity of decaying quackgrass leaves. The highest toxic effect was noted after 1 week of decay on the soil surface.

Smutgrass [Sporobolus poiretii (R. & S.) Hitchc.] in native grass and ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] pastures near Caldwell, Texas, was sprayed with herbicides in 1975 and 1976. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 4.5 kg/ha; dalapon (2,2-dichloropropionic acid) at 5.6 kg/ha; glyphosate [N-(phosphonomethyl)glycine] at 0.6 and 2.2 kg/ha; and bromacil (5-bromo-3-sec-butyl-6-methyluracil), tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at 1.1 and 2.2 kg/ha reduced smutgrass foliar cover, particularly if applied from July to November. Dalapon, tebuthiuron, and hexazinone were the most effective herbicides for reducing smutgrass foliar cover. Other grasses generally replaced smutgrass controlled with hexazinone or tebuthiuron, while broadleaf species mostly replaced smutgrass in plots controlled with dalapon or glyphosate. Dalapon, glyphosate, bromacil, hexazinone, and tebuthiuron caused some injury to Coastal bermudagrass for 3 or 4 months following treatment. By fall of the year after treatment Coastal bermudagrass cover in treated plots was equal to or greater than that in untreated plots.

Field studies were conducted in 1975 and 1976 at Urbana, Illinois, to evaluate soybeans [Glycine max (L.) Merr. ‘Amsoy 71′] as a potential rescue crop following the use of cyanazine{2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} and procyazine {2-[[4-chloro-6-(cyclopropylamino)-1,3,5-triazine-2-yl] amino]-2-methylpropanenitrile} with corn (Zea mays L.). Preplant incorporated and preemergence applications of each herbicide were made at the recommended broadcast rates to Dana and Flanagan silt loams. Corn was removed and soybeans were planted 7, 13, and 21 days (1975) or 10, 15, and 23 days (1976) following herbicide application. Visual injury ratings, stands, and yields for soybeans were determined. In spite of varying degrees of visible injury and stand reductions, yields were not reduced significantly when soybeans were planted 3 weeks after cyanazine or procyazine application.

Factors influencing dicamba drift, especially vapor drift, were examined in field and growth chamber studies. In field experiments, potted soybeans [Glycine max (L.) Merr.]. exposed to vapors arising from corn (Zea mays L.) foliarly treated with the sodium (Na), dimethylamine (DMA), diethanolamine (DEOA), or N-tallow-N,N1,N1-trimethyl-1,3-diaminopropane (TA) salts of dicamba (3,6-dichloro-o-anisic acid), developed dicamba injury symptoms. Dicamba volatilization from treated corn was detected with soybeans for 3 days after the application. Dicamba vapors caused symptoms on soybeans placed up to 60m downwind of the treated corn. When vapor and/or spray drift caused soybean terminal bud kill, yields were reduced. In growth chamber studies, dicamba volatility effects on soybeans could be reduced by lowering the temperature or increasing the relative humidity. Rainfall of 1mm or more on treated corn ended dicamba volatilization. The dicamba volatilization was greater from corn and soybean leaves than from velvetleaf (Abutilon theophrasti Medic.) leaves and blotter paper. The volatilization of dicamba formulations varied in growth chamber comparisons with the acid being most volatile and the inorganic salts being the least volatile. However, under field conditions, use of less volatile formulations did not eliminate dicamba symptoms on soybeans. The volatile component of the commercial DMA salt of dicamba was identified by gas chromatography-mass spectrometry as free dicamba acid.

Germination of seeds of 10 grass and 33 broadleaved weed species was examined for response to ethylene. Germination was promoted in nine species, inhibited in two, and not affected in the remainder. Of the species promoted, common purslane (Portulaca oleracea L.), common lambsquarters (Chenopodium album L.), and several Amaranths, including redroot pigweed (Amaranthus retroflexus L.), were affected most. Transformation of phytochrome to the active form (Pfr) gave interactions that ranged from none to syntergistic with the applied ethylene. In subsequent tests seeds of purslane, redroot pigweed, and giant foxtail (Setaria faberi Herrm.), a species not responsive to ethylene, were examined for germination response to 14 low molecular weight hydrocarbon gases other than ethylene. Some stimulation by the olefins propylene and propadiene was found for purslane and pigweed. Propionaldehyde and butyraldehyde were slightly stimulatory to purslane only.

The persistence of napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] applied at 2.24- and 4.48-kg/ha was studied for 2 yr at two locations in the field. Wheat (Triticum aestivum L. ‘Arthur 71′) was severely injured when sown in the fall following a spring application of napropamide. A wheat root bioassay also showed that napropamide was persistent for more than 180 days. The yield of sweet corn (Zea mays L. var. rugosa Bonaf. ‘Gold Cup’) was not significantly reduced when grown 1 yr after the initial application of napropamide.

Annual bluegrass (Poa annua L.) growing in bermudagrass completes its life cycle in May and dies leaving open spaces in the turfgrass. This occurs at a time when summer annual weeds are germinating and these weeds fill the space formerly occupied by the annual bluegrass. As the summer annual weeds die in the fall, annual bluegrass germinates and fills the space formerly occupied by the summer annual weeds. To control annual bluegrass, it is important to control the summer annual grasses and manage the bermudagrass [Cynodon dactylon (L.) Pers.] to maintain a competitive groundcover especially during the peak germination period for the weeds. Herbicide programs over a three-year period were designed to control annual grasses with treatments in April for large crabgrass [Digitaria sanguinalis (L.) Scop.], in May or June for goosegrass [Eleusine indica (L.) Gaertn.] and in late August for annual bluegrass. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-ozadiazolin-5-one] applied in August gave complete control of annual bluegrass. Although oxadiazon has a long residual life in the soil, annual bluegrass was poorly controlled with treatments made in June. Fall (August or September) applications of benefin [N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine], prosulfalin N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine and butralin [4-(1,1-dimethylethyl-N-(1-methylpropyl)-2,6-dinitrobenzenamine] provided adequate control of annual bluegrass with only a few exceptions during the three-year period. Bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] gave variable control of annual bluegrass; however, this was improved in programs with oxadiazon which provide goosegrass control during summer. In these studies, DCPA [dimethyl tetrachloroterephthalate], even with three applications a year, gave very little control of annual bluegrass. When oxadiazon was used in rotation with DCPA, adequate control was obtained.

Absorption of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} by tanoak [Lithocarpus densiflorus (Hook. & Am.) Rehd.] leaves was investigated. Greater amounts of 14C-triclopyr were absorbed by immature leaves than mature leaves and by abaxial than adaxial surfaces. Both surfaces of immature and mature tanoak leaves were characterized. Stomata were present only on the abaxial surface and were more numerous on immature leaves than mature leaves. Immature leaves had less epicuticular wax and thinner, more permeable cuticular membranes than mature leaves. Stellate trichome densities were greater on abaxial surfaces than adaxial surfaces and on immature than mature leaves. Absorption of 14C-triclopyr was influenced by each of the leaf surface features studied.