Seven different types of nozzles were compared as to uniformity of spray application, spray drift, and tendency to clog. The wide angle whirl chamber nozzles applied the spray more uniformly than other nozzles. Increasing nozzle height to 1.5 times the recommended height increased uniformity of spray application with most nozzles. Lowering the nozzle height to half the recommended height seriously reduced uniformity of spray application with almost all nozzles except the wide angle whirl chamber nozzles which provided a uniform spray at all 3 heights. The whirl chamber nozzles were least easily clogged of the nozzles studied. Wettable powders normally applied in 30 gallons or more per acre have been satisfactorily applied at rates of less than ¼ of this amount. Spray drift was reduced to a no crop hazard level, with effective coverage, at rates of application as low as 7 gallons per acre.

Treatment of little barley (Hordeum pusillum Nutt.) at early-tillering stages with 0.25 to 0.5 lb/A of 1,1′-dimethyl-4,4′-dipyridylium cation paraquat, surfactant gave satisfactory to complete control of little barley and other annual weed species. Except under unfavorabe seasonal conditions, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) also gave good control of little barley but was ineffective against other established weed species. Coastal bermudagrass [Cynodon dactylon (L) Pers.] was not injured by atrazine and only temporarily by paraquat.

Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv] is the foremost weed in rice (Oryza sativa L.) systems, and its control is crucial to successful rice production. Quinclorac, a synthetic auxin herbicide, has been used effectively to manage E. crus-galli. However, occurrences of quinclorac-resistant genotypes are frequently reported, and its resistance evolution has led to questions about the continued utility of quinclorac for grass control. Identification of the resistance mechanism(s) of resistant genotypes will facilitate development of integrated weed management strategies that sustain quinclorac use for management of E. crus-galli. We evaluated the responses to quinclorac of two contrasting genotypes: E7 (resistant, R) and LM04 (susceptible, S). Quinclorac induced ethylene and cyanide biosynthesis in the S-genotype. Both genotypes responded similarly to an increasing application of exogenous 1-carboxylic acid aminocyclopropane (ACC) and potassium cyanide, and their growth was inhibited at higher doses. The key mechanism for cyanide (HCN) detoxification in plants, β-cyanoalanine synthase (β-CAS) activity, was evaluated in both genotypes, and no significant difference was observed in the basal activity. However, quinclorac significantly induced β-CAS–like activity in the S-genotype, which is consistent with the increased synthesis of ethylene and cyanide. This work suggests that the resistance to quinclorac of the E7 R-genotype is likely related to an alteration in the auxin signal transduction pathway, causing a lower stimulation of ACC synthase and, therefore, limited synthesis of ethylene and HCN after quinclorac treatment.

A quantitative assay using 14C-chloramben (3-amino-2,5-dichlorobenzoic acid) revealed that velvetleaf (Abutilon theophrasti Medic. # ABUTH) leaves absorbed a greater amount of chloramben formulated as an acid than as a sodium salt. A surfactant increased 14C-chloramben absorption 5 days, but not 1 day, after application. Translocation of 14C-label out of treated leaves was greater in velvetleaf than in soybean [Glycine max (L.) Merr.]. Differences in the amount of 14C-label as unmetabolized chloramben in ethyl acetate extracts of treated leaves were not detected between velvetleaf and soybean. The amount of unmetabolized chloramben was greater in the shoot above the treated leaf in velvetleaf (58% of total label recovered) than in soybean (35% of recovered label). The amount of recovered 14C-label in unextractable form was greater in treated leaves of soybean compared to velvetleaf.

‘Forrest’ soybean [Glycine max (L.) Merr.] infested with entireleaf morningglory [Ipomoea hederacea (L.) Jacq. var. integriusula Gray] were treated in the field with three postemergence herbicides, dinoseb (2-sec-butyl-4,6-dinitrophenol), sodium salt of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid]. Foliar nitrogen (N) loss, transpiration, and CO2 equilibrium concentrations were measured from 4 to 148 h after treatment. In morningglory foliar N loss was increased by dinoseb, decreased by acifluorfen, and first increased and then decreased by 2,4-DB treatments. Transpiration in this weed species was decreased by all three herbicides. In soybean, N loss was increased and transpiration decreased with dinoseb; acifluorfen did not affect either activity; and 2,4-DB decreased both processes during one sampling period. In both plant species dinoseb increased the CO2 equilibrium concentration within 4 h after treatment. Treatments with acifluorfen and 2,4-DB initially increased the CO2 concentration in morningglory with major increases noted at the onset of chlorosis 52 h after treatment. In soybean, some significant decreases in CO2 equilibrium concentrations occurred with the lowest rate of all three herbicides.

Cogongrass is a noxious perennial grass that has invaded many countries in the tropical and subtropical regions of the world. Its management has been a significant challenge because of large rhizome and bud reserves in the soil. The emergence pattern of this weed under field conditions has received little attention. Field trials were conducted in 2002 and 2003 in the humid forest zone of southeastern Nigeria to model shoot emergence. The experiment had four treatments: (1) count and tag crop-free cogongrass shoots, (2) count and suppress crop-free cogongrass shoots with paraquat, (3) count and cut crop-free cogongrass shoots, and (4) count and cut cogongrass shoots in cultivated corn. The rationale for these treatments was to determine the effect of different monitoring techniques on shoot emergence of cogongrass. The development of the model was based on hydrothermal time, which was calculated from soil moisture and soil temperature at a 2-cm depth. A Weibull function was fitted to cumulative percent shoot emergence values of Treatment 4 and hydrothermal time. The model closely fit the observed pattern of cogongrass shoot emergence (r 2 = 0.95, n = 36). It also predicted shoot emergence satisfactorily in six treatments (r 2 > 0.85, P < 0.001, n = 7 in each treatment) that simulated farmers' practices in southwestern Nigeria. This is the first model developed for cogongrass shoot emergence based on hydrothermal time under field observations. The model should facilitate further analyses of cogongrass emergence patterns and the timing of its management.

The effect of three spray variables (droplet number, active ingredient concentration, and droplet size) on uptake and translocation of formulated 14C-triclopyr ester was studied in greenhouse-grown Populus tremuloides seedlings. The dose per plant in all treatments was held constant. In all experiments, absorption (as a percentage of dose applied) was much greater than translocation (as percentage of dose absorbed). Absorption and translocation decreased as concentration (ai) was increased and droplet number decreased. Absorption and translocation also decreased as droplet number decreased and droplet size increased. When concentration (ai) was increased and droplet size decreased, absorption again decreased but to a much lesser extent than in the other two experiments; there was no significant effect on translocation. A time-course experiment indicated that uptake rate began to decrease within 1.5 h of application. The rate of decrease was greater at the higher concentration (ai), suggesting that the decrease was associated with contact injury. A model to integrate the application parameters and translocation gave a high correlation between dose per unit droplet stain circumference and translocation.

The herbicides 2,4-D [(2,4-dichlorophenoxy) acetic acid], dalapon (2,2-dichloropropionic acid), glyphosate [(N-phosphonomethyl)glycine], paraquat (1,1’-dimethyl-4,4’-bypiridinium ion), and pronamide [3,5-dichloro-(N-1,1-dimethyl-2-propynyl)benzamide] were applied at selected rates and dates to quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE]-infested alfalfa (Medicago sativa L.) sod in 1979 and 1980 to suppress vegetation for subsequent establishment of alfalfa without tillage. The influence of herbicides on weed control, alfalfa seedling density and visual stand, and forage yield and quality was assessed for 3 yr. During establishment, all herbicides except 2,4-D effectively controlled quackgrass. Glyphosate applied broadcast increasingly suppressed the existing sod as the rate was increased from 0.6 to 1.6 kg ai/ha. The effectiveness of herbicides as measured by total (old and new) plant density was closely related to the suppression of the sward. While the substitution of new alfalfa plants for old ones was not necessary under dense (40 plants/m2) alfalfa stands, completely controlling the vegetation with glyphosate resulted in sustained productivity throughout the experimental period. After 3 yr, alfalfa percentage and yield were highest when glyphosate was broadcast at 1.6 kg/ha. Improvement in forage quality, as estimated by the concentrations of crude protein and neutral-detergent fiber, was closely related to grass control.

A comparison of the structure of the α-methylbenzyl analogue (MBAT) of atrazine with the Photosystem II herbicides atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea] suggested that N-alkylbenzyltriazines may be a structural bridge between the triazines and the phenylureas. In the phenylureas, the addition of chlorines at the meta and/or para positions produces a marked increase in activity. Chloro-substituted derivatives of MBAT were synthesized to determine whether this structure-activity relationship also applies to the alkylaryltriazines. Addition of a chlorine to MBAT at the 4-position (CMBAT) caused a substantial increase in intrinsic activity, and a second chlorine at the 3-position (DCMBAT) caused a further increase. In direct comparisons, DCMBAT was more active in vitro than terbuthylazine [6-chloro-N-ethyl-N′-(1,1-dimethylethyl)-1,3,5-triazine-2,4-diamine], the most active chlorotriazine, and was also more active than diruon. The effects of DCMBAT were also measured on triazine-resistant pigweed (Amaranthus hybridus L. # AMACH) both in vivo and in vitro. The activity of this compound in triazine-resistant chloroplasts was intermediate between that of atrazine and diruon both in inhibition of photosynthetic electron transport and in competition for diuron binding sites, with half-maximal values falling in the micromolar range. Whole plant phytotoxicity of DCMBAT on triazine-resistant pigweed was also intermediate between that of diuron and atrazine. Since DCMBAT is a triazine with biological properties similar to that of a urea, we conclude that in a functional as well as structural sense, DCMBAT is a herbicide that is a hybrid between a triazine and a urea.

Trumpetcreeper [Campsis radicans (L.) Seem.] grown from 10-cm root sections was more susceptible to foliar applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and dicamba (3,6-dichloro-o-anisic acid) than trumpetcreeper grown from 45-cm root sections. Dicamba controlled trumpetcreeper better than did 2,4-D, particularly trumpetcreeper grown from 45-cm root sections. More 14C-dicamba than 14C-2,4-D was absorbed through the foliage and translocated to the roots of trumpetcreeper grown from 10-cm roots. No 14C-2,4-D was detected in the 45-cm roots; however, 14C-dicamba was recovered from both the upper and the lower sections of the 45-cm roots.

Three years of field experiments showed that Canada thistle. [Cirsium arvense (L.) Scop.] could be controlled with deeply injected soil fumigants without covering the soil with a tarpaulin. The degree of control depended on the kind of fumigant, the rate of application, and the depth of injection. Weed control with fumigants usually improved as the rate of application and depth of injection increased. The most effective treatment was 1,3-dichloropropene at 560 kg/ha injected to a depth of 46 cm. Good to excellent control of Canada thistle was also obtained with 1,3-dichloropropene at 280 kg/ha injected either 23 or 46 cm and ethylene dibromide at 160 kg/ha and chloropicrin + ethylene dibromide at 20 + 55 kg/ha injected at 46 cm. Results with ethylene dibromide and chloropicrin + ethylene dibromide were more erratic than with 1,3-dichloropropene. Increasing the percentage of chloropicrin in the combination reduced the control of Canada thistle.

Mixtures of chlorimuron and 2,4-DB were additive with respect to crop injury and were either additive or slightly antagonistic with respect to weed control in greenhouse experiments. Absorption and translocation of 14C following application of 14C-chlorimuron and 14C-2,4-DB were not affected by the presence of the other unlabeled herbicide, except in Florida beggarweed and peanut where 2,4-DB affected distribution of 14C-chlorimuron in the treated leaf. In field studies, maximum efficacy was obtained with mixtures of chlorimuron plus 2,4-DB applied 7 or 9 wk after planting. Florida beggarweed control was greatest with chlorimuron or chlorimuron mixtures while the addition of 2,4-DB to chlorimuron improved morningglory and sicklepod control. At 9 and 11 wk after planting, addition of 2,4-DB to chlorimuron controlled Florida beggarweed better than chlorimuron alone. Peanut yields were increased by the addition of 2,4-DB at later applications.

Growth of sugarbeet (Beta vulgaris L. ‘Mono Hy A1’ and ‘Mono Hy D2′) and (B. patellaris Moq.) seedlings in cycloate (S-ethyl N-ethylthiocyclohexanecarbamate)-amended soil infested with the sugarbeet nematode (Heterodera schachtii Schmidt) was reduced (P = 0.05) at a concentration of 4 jug cycloate/g soil. Although the combination of cyloate with aldicarb [2-methyl-2-(methylthio) propionaldehyde-O-(methylcarbomyl) oxime] resulted in a significantly (P = 0.05) reduced growth of both sugarbeet cultivars and B. patellaris, it did not affect the nematicidal properties of aldicarb. Cycloate alone or in combination with aldicarb did not affect the growth of B. procumbens Chr. Sm. seedlings.

Treatments that enhanced the germination of dormant seed of dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly] the most were chilling seed at 2 C for 3 months and then scarifying with sodium hypochlorite, scarifying seed and then chilling wet seed at 7 C for 3 months, or chilling wet seed at 2 C for 24 months. Percentage of germination for these treatments were 58, 56, and 65%, respectively. Scarifying seed with sodium hypochlorite after they had been chilled wet for 12 to 24 months at 2 C reduced germination. Other treatments that significantly enhanced germination were chilling seed wet for 4 months at 2 C, scarifying dry-stored seed with a 5.25% solution of sodium hypochlorite for 10 h, and soaking seed in concentrated hydrochloric acid for 24 min. These latter treatments resulted in germination percentages of 35, 33, and 35, respectively. Eighty percent of the viable seed usually germinated within 10 days, and when germination was poor, seed lacked embryos or were empty. Dormancy appeared to be due to an impermeable seed coat and not to a germination inhibitor.

Concentrations of TCA (trichloroacetic acid) were determined in irrigation water after the sodium salt formulation had been applied to the banks of dry canals at 82 kg/ha for weed control. When the canals were refilled about 5 months after treatment, maximum concentrations of TCA detected in the water ranged from 53 to 297 ppb. The concentration was highest during the first hour of waterflow. The maximum concentration increased at a rate of 26 to 30 ppb/km of canal treated, unless surface runoff or reduced flow volumes caused abnormal flows in the canals. With one exception, no TCA was detected in the water after 4 hr of flow.

The metabolism of 3′,4′-dichloropropionanilide (propanil) to 3,4-dichloroaniline (hereinafter referred to as 3,4-DCA) and N-(3,4-dichlorophenyl)glucosylamine (hereinafter referred to as 3,4-DCAG) was quantitatively modified in rice (Oryza sativa L. ‘Nato’) by temperature and day length. The propanil, 3,4-DCA, and 3,4-DCAG content of rice was determined 1, 2, 5, and 8 days after root treatment with 92 μM propanil. Plants were grown and treated under long-day (16 hr) and short-day (12 hr) conditions with day temperatures of 32, 27, or 21 C and night temperatures of 21 C. Absorption and metabolism of propanil were most rapid under high temperature and long day conditions. A mean value of 0.75 μmoles total of aniline equivalent per plant was obtained. Greater quantities of 3,4-DCA and 3,4-DCAG were recovered from plants in high temperature, long day environments. An average of 47% of the propanil plus water-soluble metabolites in rice was in root tissue. Conditions favoring high growth rates and transpiration increased the percentage in the shoots. Because of the increased tissue mass at high temperatures, mean concentrations of propanil plus water-soluble metabolites in plant tissue were reduced from 0.18 to 0.12 μmoles/g dry weight.

Seedling alfalfa exhibited increased phytotoxicity from bromoxynil when applications were made with temperatures greater than 28 C both in controlled environments and in the field. Treatments applied in the morning were more phytotoxic than treatments made in the late afternoon. In laboratory experiments, inhibition of oxygen evolution occurred within 1 h after treatment. The amount of permanent damage sustained was dependent on the rate of bromoxynil and the length of time the alfalfa was exposed to light or darkness immediately after spraying. Bromoxynil treatments in cool weather and/or in the late afternoon should minimize injury to the crop.

The persistence of isopropalin (2,6-dinitro-N,N-dipropylcumidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) applied at recommended (1X) and high (2X) rates was studies in the field on two soils. A sorghum [Sorghum bicolor (L.) Moench ‘RS 610’] root bioassay showed that the recommended rates of the herbicides caused 20% or less root inhibition at the end of the growing season in 1972. Both nitralin and trifluralin were more persistent in 1974 than in 1972 as shown by the root bioassay and growth of fall-sown rye (Secale cereale L.). 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 the herbicides.