These studies were conducted in the laboratory on two soils at two temperatures to define the rate of degradation and the associated rate law for trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), and 2,6-dinitro-N-(3-pentyl)-α,α,α-trifluoro-p-toluidine (hereafter referred to as Unnamed). Rate of degradation was directly correlated with temperature and moisture content. First order kinetics adequately described the rate of degradation at 15 C, but the simple first order assumption was not sufficient to describe degradation at 30 C. The implication of our interpretation is that at 30 C two rate processes may operate in the soil degradation of these three dinitroaniline herbicides. The data show an initial rapid first order rate of degradation with a subsequent change to a slower first order process. First half lives ranged from 0.4 to 1.8 months at 30 C and were consistently lower in a loam than in a sandy loam soil.

Rhizomes of quackgrass [Agropyron repens (L.) Beauv.] and johnsongrass [Sorghum halepense (L.) Pers.] were buried at various depths in the soil in the fall of 1972 and 1973, then removed at different times for viability tests. Quackgrass rhizomes retained viability at 2 cm where the coldest temperatures were −17 C. Johnsongrass rhizomes survived the winter at depths of 20 cm or more, and were killed at temperatures below about −9 C. Quackgrass rhizomes had a higher concentration of lipids and higher proportions of unsaturated fatty acids than did johnsongrass rhizomes. This difference may contribute to the superior cold tolerance of the quackgrass rhizomes.

Peanut (Arachis hypogaea L. ‘Florigiant’) seed yield was reduced 25% by a fall panicum (Panicum dichotomiflorum Michx.) density of one weed per 4.9 m of row. Greater weed densities resulted in greater yield losses. Peanut seed yield was reduced by fall panicum interference for 2 weeks or more after peanut emergence. Peanuts kept weed-free for 8 weeks after emergence failed to yield as well as those kept weed-free all season. However, control for the first 2 weeks appeared to be the most critical.

Persistence of 1.12, 2.24, and 3.36 kg/ha of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied preemergence to corn (Zea mays L. ‘Funk's 4761′) was determined in three soils, each providing a range of pH from 5 to 7. Samples of surface soil from each plot were collected at intervals after atrazine application until there was no evidence of phytotoxicity to oat (Avena sativa L. ‘Florida 501′) in bioassay. Persistence (Y50) was defined as the number of days following atrazine application until bioassay indicated 50% relative growth of oats (no atrazine = 100% growth). This period ranged from 24 to 178 days, depending upon soil type, pH, and atrazine rate. Persistence of atrazine increased with increasing soil pH. The effect of soil pH was essentially the same at each atrazine rate and did not vary appreciably with years in a given soil. In McLaurin sandy loam, atrazine persisted 8 to 9 days longer with each unit increase in soil pH. In Hartsells fine sandy loam and Decatur silt loam, atrazine persistence increased 9 to 13 days and 29 days, respectively, with each unit pH.

Emulsifiable cationic (CM-4,CRS-1H,CSS-1,CSS-1H) and anionic (SS-1H) asphalts mixed with bromacil (5-bromo-3 sec-butyl-6-methyluracil) varied in their toxicity to green foxtail [Setaria viridis (L.) Beauv.] and velvetleaf (Abutilon theophrasti Medic). Bromacil, picloram (4-amino-3,5,6-trichloropicolinic acid), prometone [2,4-bis(isopropylamino)-6-methoxy-s-triazine], and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea} mixed with CRS-1H or CSS-1H gave excellent control of green foxtail and velvetleaf. In greenhouse experiments prometone leached readily from SS-1H while bromacil, picloram, and tebuthiuron leached the least. Leachate from picloram and tebuthiuron at 10,000 ppmw gave excellent control of green foxtail and velvetleaf. After leaching combinations of bromacil or tebuthiuron in SS-1H asphalt with 554 cm of water, enough herbicide still remained in the asphalt to control green foxtail and velvetleaf. Results indicate control would persist for 7 yr if annual rainfall was 76 cm or less and the herbicides were applied at 10,000 ppmw. Bromacil, picloram, prometone, and tebuthiuron moved laterally and resulted in more vegetation kill along a highway shoulder than on a level smooth brome (Bromus inermis Leyss.) area. Herbicide rates of 1,000 and 10,000 ppmw often resulted in excessive lateral movement and vegetation kill 2 yr after treatment. Combining herbicides with asphalt appears to be a feasible method of controlling weed growth, reducing lateral herbicide movement, and lengthening herbicide persistence.

The use of electrolytic conductivity as a measure of cell membrane disruption was tested on buckwheat (Fagopyrum esculentum Moench. cv. ‘Tokyo’) plants which had been sprayed with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. All treatments which resulted in tissue damage caused significant increases to the solutions where the discs were floated for measurement. The highest conductivity measurement (most membrane disruption) was obtained from paraquat. The highest concentration for each herbicide gave higher conductivity measurements than lower concentrations. A difference in the pattern of conductivity change induced by the two chemicals implies a different mode of action for each.

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.

Production of native grasses following aerial application of 1.12 kg/ha of 2.4.5-T ((2,4,5-trichlorophenoxy)acetic acid), 2,4,5-T + dicamba (3,6-dichloro-o-anisic acid), or 2,4,5-T + picloram (4-amino-3,5,6-trichloropicolinic acid) (1:) to a south Texas mixed-brush (Prosopis-Acacia) community was significantly increased by all herbicide treatments the year of application, by the herbicide combinations during the second year, but only by 2,4,5-T + picloram the third year after treatment. Moisture-use efficiency based on kg/ha native grass produced/cm precipitation was greastest where the herbicide combinations were applied. Defoliation of woody plants in years of above-average rainfall resulted in favorable grass production responses regardless of herbicide(s). However, range improvement over the 3-yr of study was dependent on maintenance of herbicide effectiveness, especially control of underbrush which resulted only where 2,4,5-T + picloram were applied. Consumption of native grass was a direct function of availability in response to brush control as augmented by rainfall. Forb production was reduced by all herbicides the year of treatment and by 2,4,5-T + picloram the year following application, but was not reduced by any treatment during the third growing season.

The effects of soil-applied and stem-injected herbicidal techniques of forest conversion on soil moisture, pine establishment and understory vegetation were determined in an Appalachian hardwood forest. Grid applications of fenuron (1,1-dimethyl-3-phenylurea) at 11.2 kg/ha were as effective in killing tops and controlling sprouting of hardwood species as the injection application with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and fuel oil. Survival of white pine (Pinus strobus L.) was higher with 5.6 kg/ha than with 11.2 kg/ha of fenuron pellets. The growth in height of pines growing under reduced competition was considerably greater than for pines growing in competition with hardwoods. During the second growing season after treatment significantly more soil moisture was present in the plots treated with fenuron and 2,4,5-T than in the untreated ones. Herbaceous vegetation and understory woody plants increased after the herbicide treatments. The third season following herbicide treatment twenty-seven species were recorded on the treated areas that were not present on the untreated control areas.

Ethofumesate (2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate) applied preemergence or early postemergence at 0.8 to 4.5 kg/ha eliminated annual bluegrass (Poa annua L.) in Italian ryegrass (Lolium multiflorum Lam.) seed fields. Rattail fescue (Festuca myuros L.) was more difficult to control. The 0.8 kg/ha rate controlled only 55% of the rattail fescue. Rates of 1.1 to 1.7 kg/ha controlled 72 to 95% and rates of 2.2 to 4.5 kg/ha eliminated rattail fescue. All ethofumesate treatments except one, 2.2 kg/ha applied postemergence in Experiment 7, reduced weed competition enough so that ryegrass seed yields were increased. At 4.5 kg/ha, a rate double that required to eliminate rattail fescue, seed yields were as high or higher than at 2.2 kg/ha rate, indicating that ethofumesate has at least a twofold safety margin on Italian ryegrass. The germination of ryegrass seed harvested from plots treated with ethofumesate at 0, 2.2, and 4.5 kg/ha was not affected by the treatments.

Sugarcane (Saccharum interspecific hybrids) grown without cultivation but maintained relatively weed-free with herbicides and hand hoeing, produced yields of sugarcane/ha and sugar/ha in the plant, first-ratoon, and second-ratoon crops that were 100%, 95%, and 88%, respectively, of the yield of sugarcane cultivated two to four times annually. Standard cultural practice involves at least two cultivations, namely, the off-barring and the fertilizational cultivations. Additional cultivations did not substantially increase yield. When sugarcane yield was affected either by cultivation or herbicide treatment, stalk population rather than stalk weight was affected the most. Johnsongrass [Sorghum halepense (L.) Pers.] and annual weeds were controlled effectively in both cultivated and non-cultivated sugarcane with broadcast, preemergence application of fenac [(2,3,6-trichlorophenyl)acetic acid] at 5 kg/ha or terbacil (3-tert-butyl-5-chloro-6-methyluracil) at 1.8 kg/ha. Purple nutsedge (Cyperus rotundus L.), however, was controlled only with a combination of fenac or terbacil and periodic cultivation.

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 tolerance of wheat (Triticum aestivum L. ‘Waldron’) and wild oat (Avena fatua L.) to various rates of flufenprop-methyl {methyl-2-[benzoyl(3-chloro-4-fluorophenyl)amino]propanoate} applied weekly after wheat and wild oat emergence was determined under field conditions. Wild oat control increased at all growth stages as flufenprop-methyl rate increased. Wild oat control was greater than 80% with flufenprop-methyl at all rates when applied up to 6 weeks after wild oat emergence: (anthesis stage), but decreased when application was delayed further. Wheat was most susceptible to flufenprop-methyl during anthesis. Flufenprop-methyl at 0.56 kg/ha injured weed-free wheat only at the boot and anthesis stages. Injury intensity and the number of weeks that injury remained evident increased as flufenprop-methyl rate increased. Flufenprop-methyl injury to wheat was expressed as reduced plant height, grain yield, and kernels per spike and increased grain protein. Plant height reductions were attributed to reduced cell elongation. Grain yield reductions resulted from reduced kernels per spike.

The persistence of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one] in several soils from the lower alluvial floodplain of the Mississippi River was studied in the greenhouse and laboratory using bioassay and gas chromatographic methods of residue detection. Bioassay results indicated that metribuzin phytotoxicity was lost in several soil types within a few weeks of application. Longevity of phytotoxicity depended upon soil type. However soil type had little effect on the rate of metribuzin degradation measured chemically. Gas chromatographic techniques indicated that metribuzin degradation followed first-order kinetics with half-life values ranging from 17 to 28 days in six soils under greenhouse conditions. Incubation studies indicated that metribuzin was degraded more rapidly in nonautoclaved field soil and in soil enriched with glucose than in soil that had been air dry for 1 yr or had been autoclaved. Degradation was more rapid at 30 C than at 20 C. Microbiological activity apparently is important in the degradation of metribuzin in soil.

Silverleaf sunflower (Helianthus argophyllus Torr. & Gray) is a weed in the sandy soils of south and southeast Texas. The young plant parts are densely white-tomentose. This pubescence greatly increased laboratory and field-measured light reflectance over the 0.5- to 2.5-μm waveband compared with the sparsely-hairy leaves of common sunflower (Helianthus annum L.). This increased reflectance caused silverleaf sunflower's image on Eastman Kodak Aerochrome infrared color type 2443 film to be “pinkish” compared with darker magenta images for other plant species. Therefore, aerial photography may be useful to distinguish silverleaf sunflower plants from other plant species to locate its endemic areas, monitor its spread, and delineate areas needing weed control.

Eight substituted dinitroaniline herbicides were studied for relative effectiveness in controlling weeds and for tolerance of peas (Pisum sativum L.). Greenhouse trials comparing 10-5 M herbicide solutions added to washed silica sand indicated that trifluralin (α,α,α-trifluroro-2,6-dinitro-N,N,-dipropyl-p-toluidine) and dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) were the most phytotoxic to peas. Field trials conducted over a 3-yr period using 0.84 and 1.68 kg/ha application rates demonstrated that all eight of the herbicides successfully controlled the weeds present. Use of trifluralin resulted in the lowest shelled pea yields at both rates of application. Significant reductions in yield occurred from the 1.68 kg/ha rate of trifluralin in 1973 and 1975 when compared with the untreated checks. While major differences did not occur between the other chemicals, the greatest average pea yields resulted from the use of oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), dinitramine, and fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)analine].

Mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl]amino] phenyl] acetamide} at concentrations of 2.9 × 10-4 M and above retarded the growth of corn (Zea mays L. ‘Pioneer 3369A’) grown in nutrient culture. Dwarfing was accompanied by some plant distortion and chlorosis of the bases of those leaves formed soon after treatment. The chlorosis was associated with decreased chlorophyll a content. Chlorophyll b content was not affected. The growth-retardant effects of mefluidide could not be reversed by applications of gibberellic acid. Using cucumber (Cucumis sativus L. ‘Ashley’) cotyledon discs, a low level of mefluidide (2.9 × 10-5 M) increased the incorporation of 14C from leucine into protein, while a high concentration (2.9 × 10-4 M) reduced incorporation. Neither concentration affected the absorption of 14C-leucine.

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.