A new method was developed for incorporating herbicides into the root zone of saltcedar (Tamarix pentandra Pall.) in arid, low rainfall areas. A spray pipe with five nozzles was mounted along the rear edge of a 2.44-m root plow blade. A supply line connected the spray pipe with a sprayer mounted on the plow frame. In operation, the saltcedar roots were severed at a selected depth by the blade as herbicide was sprayed simultaneously into the cut-root zone. A similar root plow with a 1.22-m blade was designed for use on small research plots.

The selectivity of 4-chloro-2-oxobenzothiazolin-3-ylacetic acid (benazolin) in wild mustard [Brassica kaber (DC.) L. C. Wheeler var. pinnatifida (Stokes) L. C. Wheeler], turnip rape (Brassica campestris L. ‘Echo’), and rape (Brassica napus L. ‘Target’) was studied. On an ED50 basis wild mustard was 19 and 32 times more susceptible to foliar-applied benazolin than was turnip rape and rape, respectively. The addition of surfactant increased the toxicity of benazolin to the Brassica species. Benazolin was less selective when applied via roots. Selectivity was further studied on the bases of differential spray retention and foliar penetration. Rape retained less spray than did wild mustard and turnip rape. The inclusion of surfactants in formulations increased spray retention by rape. Less 14C-benazolin penetrated leaves of the rape species as compared to wild mustard. Surfactant enhanced penetration of 14C-benazolin into leaves of the three species. Leaf surface features which resulted in high spray retention and rapid penetration of benazolin partly explained the susceptibility of wild mustard. The variation in tolerance between the two rape species was attributed to differential spray retention.

Injury to corn (Zea mays L.) from S-ethyl diisobutylthiocarbamate (butylate) was investigated with respect to hybrid. Field experiments in 1971 at Dillon and Clemson, South Carolina, established that the corn hybrid ‘Coker 71’ was more tolerant to butylate than ‘Pioneer 511A’. Also established as being tolerant and sensitive to butylate were the hybrids ‘Pioneer 3030’ and ‘PAG 644’, respectively. Laboratory studies with 14C-butylate showed that the resistant hybrid ‘Pioneer 3030’ took up less 14C-butylate and metabolized more to 14CO2 than did ‘PAG 644’.

Activated carbon, applied over the seeded row in a band 2.5 cm wide, protected grasses from herbicides applied preemergence. The carbon rate required to protect the grasses varied with the grass species, the herbicide, and the rate of herbicide application. Most of the herbicides controlled weeds effectively between the rows. The herbicides usually controlled weeds less effectively within the carbon bands. Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] was inactivated most readily by the carbon and showed the greatest safety margin on the crop species. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], and terbacil (3-tert-butyl-5-chloro-6-methyluracil) required higher carbon rates for crop protection than diuron and showed a much narrower safety margin on crops. Use of this technique made possible the effective control of weeds during establishment and, subsequently, the production of high quality seed in the first seed crop.

Experiments were conducted to compare the drift of low-expansion foam and conventional sprays in a low-speed horizontal wind tunnel under controlled environmental conditions. Dimensions of the tunnel were 1.30 m high, 0.61 m wide, and 7.32 m long. Wind speed was maintained at 1.52 m/sec. Drift was compared for spray solutions, with and without foam adjuvants, using several different types and sizes of air-inducting nozzles and three sizes of conventional fan nozzles. Large drops produced by the air-inducting nozzles, with and without foam adjuvant, resulted in significantly less drift beyond 1.83 and 6.10 m than sprays from the conventional fan nozzles. The addition of foam adjuvant to the spray solution resulted in increased drift beyond 1.83 m for sprays from the air-induction nozzles in several comparisons but did not result in a significant increase in the drift beyond 6.10 m.

Tolerance of greenhouse-grown soybean (Glycine max (L.) Merr.) to preemergence applications of 4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one (metribuzin) was greatly influenced by herbicide rate, soil organic matter, and simulated rainfall after treatment. Planting depth affected tolerance in cases where effects of the other variables were marginal. Severe injury was observed with 1.1% soil organic matter except at the 0.56 kg/ha herbicide rate with no rainfall for 10 days after treatment. Tolerance increased with increasing soil organic matter to the point where no injury occurred at 16.8 or 40.0% organic matter, even at herbicide rates up to 1.68 kg/ha with 1.25 cm simulated rainfall immediately after treatment.

The evapotranspiration of six dominant emersed and floating weeds was studied. Evapotranspiration of water-chestnut (Trapa natans L. var. bispinosa Roxb.), waterlettuce (Pistia stratiotes L.), and swamp morningglory (Ipomea aquatica Forsk.) did not increase water losses significantly. Evapotranspiration of waterhyacinth (Eichornia crassipes (Mart) Solms.) was 30 to 40% higher, that of narrowleaf cattail (Typha augustifolia L.) was 60 to 70% higher, and that of purple nutsedge (Cyperus rotundus L.) was 130 to 150% higher than evaporation from a free water surface under equivalent conditions. Positive correlations (significant at the 1% level) were found between some meterological factors (daily maximum air temperature and daily average wind velocity), evaporation from free water surface, and evapotranspiration from aquatic plants studied.

Fumigation of tomato (Lycopersicon esculentum Mill. ‘Sheyenne’) with low levels of O3 had little effect on root absorption, translocation, or conversion of diphenamid (N,N-dimethyl-2,2-diphenylacetamide) to water-soluble conjugates. However, the proportion of specific conjugates was markedly altered in O3-fumigated plants. Twenty-four hours after treatment, the predominant conjugates formed in nonfumigated and fumigated tomato were the β-glucoside (MDAG), and the β-gentiobioside (MDAGB), respectively, of N-hydroxymethyl-N-methyl-2,2-diphenylacetamide. The ratio MDAG:MDAGB was 8.2:1.0 in nonfumigated tissue and 0.6:1.0 in O3-fumigated tissue. This marked shift toward production of the more polar MDAGB was accompanied by a trend toward increased production of methanol-insoluble residues. A compound having limited stability was extracted from tomato; its probable structure was N-hydroxymethyl-N-methyl-2,2-diphenylacetamide (MODA). It is a postulated intermediate in the formation of MDAG and MDAGB from diphenamid.

In comparative evaluation of adjuvant effects in eight species, nonionic silicone-glycol surfactants enhanced the activity of six herbicides to a greater extent than a standard organic surfactant, whereas cationic amino silicone surfactants enhanced to a lesser extent. The efficacy of the nonionic silicones was associated with (a) a greater enhancing action in species, particularly grasses, that were relatively resistant to herbicides applied without adjuvants and (b) a greater ability to enhance herbicides with very low water solubility. The cationic silicones in combination with some of the herbicides provided less enhancement in moderately sensitive crops than did the standard organic surfactant but provided equivalent enhancement on some weeds. The threshhold concentration for enhancement by silicone-glycols was 0.01% in a susceptible species and 0.1% in a resistant species. In yellow nutsedge (Cyperus esculentus L.), a silicone-glycol surfactant at a concentration of 0.5% provided greater enhancement of several herbicides than any of three organic surfactants or an emulsifiable oil.

The fate of 4-chloro-2-oxobenzothiazolin-3-ylacetic acid (benazolin) in wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler], turnip rape (Brassica campestris L. ‘Echo’), and rape (Brassica napus L. ‘Target’) was investigated with the aid of 14C-benazolin. The label was more mobile in wild mustard than the rape species following leaf treatment and accumulated in young leaves, stem, and stem apex. The label was also found in foliage after root treatment. In both cases, the translocated label was primarily that of 14C-benazolin, implying phloem and xylem transport. The susceptibility of wild mustard and tolerance of the rape species to foliar-applied benazolin can be partly explained by different rates of transport to susceptible meristematic sites. Root exudation of the label following leaf treatment was greater in wild mustard than in the rape species and was not correlated with selectivity. Labeled benazolin was rapidly metabolized by the Brassica species to four derivatives which appear to be less toxic than benazolin. Specific differences in metabolism were not sufficient to explain selectivity. Negligible amounts of 14CO2 were released by the three species following treatment with 14C-benazolin.

Fumitory (Fumaria officinalis L.) achenes were after-ripened in moist sand at 4 C for 0, 15, 30, 45, and 60 days. Embryo size in longitudinal section increased 14 times during after-ripening. The percentage of ether soluble lipids and their fatty acids remained constant during the entire after-ripening period. Soluble carbohydrates were the highest at the 45-day period of after-ripening when embryo growth was rapid. The concentration of 70% ethyl alcohol soluble amino acids increased gradually over the first 45 days of after-ripening and decreased over the last 15 days as embryo growth became more rapid.

This investigation was initiated in 1954 at Beltsville, Maryland, to determine the initial and long-term response of vegetation to, and persistence of, massive quantities of herbicides. Vegetative responses were determined 1, 2, 3, and 15 years after treatment. Residual phytotoxicity and herbicide residues were determined 14 years after treatment with bioassay and chemical analysis. After 3 years, revegetation was nearly complete in plots treated with massive (up to 400 times recommended agricultural rates) quantities of fenuron (1,1-dimethyl-3-phenylurea), monuron [3-(p-chlorophenyl)-1,1-dimethylurea], dalapon (2,2-dichloropropionic acid), chlorpropham (isopropyl m-chlorocarbanilate), sodium chlorate, 2,4-D [(2,4-dichlorophenoxy)acetic acid], borax, sodium chlorate plus borax, and 2,4-D plus borax. Only diuron [3-(3,4-di chlorophenyl)-1,1-dimethylurea], DMU [3-(3,4-dichlorophenyl)-1-methylurea] sodium arsenite, and sodium arsenite plus sodium chlorate gave residual control of vegetation for more than 3 years. Revegetated plots were identical to untreated check plots whether the vegetation was initially killed by chemical or mechanical methods. Phytotoxic soil residues of DMU, diuron, and arsenate were present 14 years after application.

Two clones of field bindweed (Convolvulus arvensis L.) which differed in their susceptibility to (2,4-dichlorophenoxy)acetic acid (2,4-D) under field and greenhouse conditions also exhibited similar differences when stem cells were cultured in liquid and agar media. Amino acids added to the culture media altered the response to 2,4-D. Glutamic acid increased the tolerance of the susceptible (S) clone, but reduced the tolerance of the resistant (R) clone. Glutamine increased the susceptibility of the S clone to a much greater degree than it did the R clone. No significant differences were noted in the rates of absorption of metabolism of 2,4-D by the two clones. Glutamine increased and glutamic acid decreased 2,4-D absorption by both clones. Levels of nitrate reductase activity (NRA), soluble protein (SP), and gross RNA (GR) increased in the S tissues but decreased or remained constant in the R tissues exposed to 4.5 × 10−5M 2,4-D. Correlations between 2,4-D susceptibility and NRA demonstrated a relationship between the effects of 2,4-D and nitrogen metabolism. Differential binding of 2,4-D within the cells appears to be the most likely explanation for the differences in response to 2,4-D.

Degradation of SAN 6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] and SAN 9789 [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone] was studied in a sandy loam soil at temperatures of 5, 20, and 35 C. After 210 days of incubation 10, 80, and 97% of SAN 6706 had been dissipated from soil at 5, 20, and 35 C., respectively. SAN 6706 was converted to SAN 9789 and a demethylated metabolite in the soil. SAN 9789 was converted to the demethylated metabolite. It was difficult to differentiate between first and second-order kinetics in the degradation of these compounds. SAN 6706, at 20 and 35 C, had a half life of 50 and 9 days respectively, and an Arrhenius activation energy of 15.8 Kcal/mole. SAN 9789, at 20 and 35 C, had a half life of 270 and 70 days, respectively, and an activation energy of 11.8 Kcal/mole. The degradation of SAN 6706 was inhibited by a chloroform treatment, and microbiological degradation is suggested.

We have shown by means of laboratory experiments with a wide range of soil types that the decomposition rate of picloram (4-amino-3,5,6-trichloropicolinic acid) in soil is dependent on soil temperature and moisture content and to no significant extent on organic matter, sand, silt, clay, pH, or initial concentration. A fractional order rate law (0.8) describes the disappearance rate best. It was not possible to develop a suitably precise equation for prediction of loss rate as affected by the above soil and climatic factors. Application of the Arrhenius equation to the data indicates an activation energy of 5.4 kcal/mol for the decomposition of picloram in soil, thus suggesting that the reaction is biological rather than chemical.

Mucilage was detectable on the seeds of 8% of 233 plant species collected in Nevada and adjacent California. Mucilaginous species were restricted to the Cruciferae, Euphorbiaceae, Labiatae, Onograceae, and Plantaginaceae. Many of the species with mucilaginous seed coats are weeds. Mucilage may influence seed dispersal and greatly influences moisture relations during germination.

Field experiments were conducted from 1967 to 1971 to determine the influence of incorporation and time of application on the performance and persistence of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Both grass and broadleaf weeds were effectively controlled by atrazine on all dates of application. Both the 2.8 and 5.6 kg/ha rates were effective as preplant incorporated or preemergence treatments. Persistence of atrazine did not differ with respect to method of application. Applications of atrazine made in April and May were degraded more rapidly than were applications made in February and March. Loss curves generally corresponded to a first-order reaction with atrazine showing an average half-life of 20 days from February to July.

The persistence of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) residues under greenhouse conditions was affected by levels of activated carbon added to a silica sand potting medium and by up to four consecutive crops of corn (Zea mays L.). Degradation of atrazine within the sand and removal by the corn crops were both reduced by activated carbon. Atrazine removal by successive crops of corn reduced injury to oat seedlings grown on the sand alone, and absorption by 1.2 g of carbon per kilogram of sand prevented oat injury both with and without cropping. Although 0.4 g/kg of activated carbon inhibited atrazine removal by corn, oat seedlings were not protected from the residues remaining. When exposed to alternate freezing and thawing, the ability of 0.4 g/kg of activated carbon to deactivate atrazine was reduced causing increased oat injury.

Fenac [(2,3,6-trichlorophenyl)acetic acid] and its sodium salt were incorporated in polyethylene matrices under varied conditions to afford a series of herbicide-polyethylene formulations. Diffusion within the matrix determined the rates at which the herbicides were released from the formulations into water. Release rates of the herbicides were altered significantly if (a) the formulation curing conditions were varied, (b) the initial amount of herbicide in the matrix was varied, (c) the solubility of the herbicide was changed, or (d) if an additive was used. The results indicate that herbicide diffuses from the matrix through water-filled cracks and capillary channels.

The physiological basis for tolerance and susceptibility of four lines of cucumber (Cucumis sativus L.) to the methyl ester of 3-amino-2,5-dichlorobenzoic acid (chloramben) was investigated. ‘MSU 3207’ and ‘MSU 0612’ were tolerant (T), whereas ‘MSU 3159’ and ‘MSU 0866’ were susceptible (S). Intraspecific variability was related to higher concentrations of chloramben in the roots of the susceptible lines, resulting from metabolic differences in these lines and rapid absorption of the herbicide by the roots of ‘S-MSU 3159’. Tolerance of ‘T-MSU 3207’ resulted primarily from low uptake and reduced translocation of the herbicide, while tolerance of ‘T-MSU 0612’ was related to, but not necessarily explained by, a peculiar 14C-label distribution pattern in the leaves. Thin-layer chromatographic analysis of methanol-soluble extracts from the lines studied 3 days after 14C-chloramben methyl ester treatment separated six 14C-metabolites in the roots and five in the shoots. After a 4-hr treatment, 14C-chloramben methyl ester was absorbed and translocated more rapidly than 14C-chloramben by all four lines. Tolerance or susceptibility did not always correlate with the total concentration of radioactivity in methanol-soluble shoot and root extracts.