Plots in dense quackgrass (Agropyron repens) sods were treated with 5-bromo-3-isopropyl-6-methyl uracil (isocil) or 5-bromo-3-sec-butyl-6-methyl uracil (bromacil) at rates of 0.5 to 4.0 lb/A in the fall or in the early spring and then planted to corn. Quackgrass was virtually eliminated by all rates but 0.5 lb/A. Corn was severely injured on plots treated at 2 lb/A but made fair growth at rates of 1.0 lb/A or less. The year following corn, soil residues of isocil were more toxic to oats than those of bromacil. Carbohydrate analyses of rhizomes from treated plots indicated that depletion of carbohydrate reserves contributed to the elimination of the quackgrass.

Adsorption of l-butyl-3-(3,4-dichlorophenyl)-l-methyl-urea (neburon), determined spectrophotometrically, varied considerably among representative soils of six Hawaiian great soil groups, ranging from 29% in Lualualei soil to 94% in Honouliuli soil. The adsorption of neburon was strongly correlated with organic matter and total soil nitrogen; other soil properties were not related.

Initial and residual neburon phytotoxicity to oats in the greenhouse was dependent on total soil nitrogen, organic matter, and the degree of neburon adsorption. Based on ED50 values, neburon toxicity in soil types decreased in the following order: Lualualei, Wahiawa, Mahana, Paaloa, Waimanalo, Kapaa, and Honouliuli. Complete neburon inactivation was obtained in Honouliuli and Waimanalo soils within the 150-day duration of this experiment, and nearly complete inactivation in Mahana and Kapaa soils.

Two propagules, axillary tubers of American pondweed and subterranean tubers of floating-leaf pondweed, previously undescribed, are reported. (Results for the first 4 yr of an 8 yr study of the yields of propagules certain aquatic plants grown are reported.) Single propagules of were planted April 1 in California or May 1 in Montana and harvested at the end of the growing season. Two types of propagules were studied, seeds and specialized asexual disseminules. (The latter included subterranean and axillary tubers, axillary buds, and stem segments.) The yields of seeds ranged from 0 with three species to over 2,000,000 with horned pondweed. One culture of sago pondweed formed over 36,000 subterranean tubers. Over 49,000 and 23,000 axillary propagules were produced by leafy and curlyleaf pondweeds, respectively.

August, September, and October were the most productive months for the development of propagules. The period varied with each species.

A Whirl jet nozzle and a flat, fan-type nozzle produced similar spray patterns when used for aerial spraying so that no reduction in drift could be obtained by the use of either nozzle. Wind speeds of 3 to 4 mph caused drift more than 80 ft to the leeward of the flight line with both nozzles.

A technique was developed for the bioassay in 48 to 84 hours of herbicides in soil or of herbicidal solutions applied to sand. Sorghum seedlings are grown against the lids of petri dishes which are filled with a moistened sand or soil medium. A modification of this technique allows the assessment of the relative importance of uptake by the root and the shoot of a range of herbicides incorporated in sand or soil.

Ethyl N,N-dipropylthiolcarbamate (EPTC), 2,3-dichloroallyl N,N-diisopropylthiolcarbamate (diallate), 2-chloroallyl-N,N-diethyldithiocarbamate (CDEC), and possibly 2-chloro-N,N-diallylacetamide (CDAA) are dependent on uptake via the shoot prior to emergence for their characteristic toxic effects. Isopropyl N-(3-chlorophenyl) carbamate (CIPC), 2,6-dichlorobenzonitrile (dichlobenil), and 2,6-dinitro-N,N-dipropyl-4-trifluoromethylaniline (trifluralin) can exert their action through direct uptake by the shoot, but root uptake appears to be much more effective. A number of other compounds appear to be ineffective when uptake is via the shoot from moistened sand.

In studies of the effect of root temperature on the toxicity of 2,4-dichlorophenoxyacetic acid (2,4-D) to rubber rabbitbrush (Chrysothamnus nauseosus (Pall.) Britton), 75 F resulted in the highest mortality following 2,4-D treatment. Root temperatures had no effect on leaf cuticle thickness. In similar studies with Canada thistle (Cirsium arvense (L) Scop.) and Russian knapweed (Centaurea repens L.), little injury resulted from 2,4-D treatment at 45 F whereas at 90 F in Canada thistle and at 60, 75, and 90 F in Russian knapweed, severe injury and/or death resulted.

The relationship between susceptibility of certain plant species to 4,6-dinitro-o-sec-butylphenol (DNBP) and their capacity to accumulate externally supplied P32, and to form ATP in leaf disks was studied. A correlation was found between susceptibility of the species to DNBP and their capacity for P32 accumulation and ATP synthesis. Therefore, it was postulated that susceptibility depends upon the level of ATP in the tissues.

In soil enrichment studies, the microbial degradation of 2,2-dichloropropionic acid (dalapon) was inhibited in the presence of 3-amino-1,2,4-triazole (amitrole), but dalapon had little or no effect on behavior of amitrole. Phytotoxic residues of the herbicides persisted longer in soils when the herbicides were applied in combination than when each was used individually. Although amitrole disappeared rapidly from all amitrole-treated soils, dalapon, when applied in combination with amitrole, disappeared more slowly than when used alone. Dalapon did not affect the behavior of amitrole in muck soil, but affected the availability of amitrole in Hagerstown silty clay loam treated with high rates of amitrole.

The compounds 3-(p-chlorophenyl-1,1-dimethylurea (monuron), 5-bromo-3-sec-butyl-6-methyluracil (bromacil), 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis (ethylamino)-s-triazine (simazine), 1,1′-dimethyl-4,4′-dipyridylium salt (paraquat), and 3-amino-1,2,4-triazole (amitrole) were added to a complete nutrient medium on which chlorotic Nicotiana tobacum was grown in the dark. Herbicide concentrations generally were 0, 10-4, 10-5, 10-6, and 10-7 molar. Callus growth was inhibited by molar concentrations greater than 10-7 for the triazines, 10-5 for monuron, 10-4 for bromacil, 10-6 for paraquat and amitrole. At these concentrations, interference with a mechanism other than photosynthesis was responsible for inhibition of growth.

Foliar absorption of carboxyl-labeled 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) by mesquite [Prosopis juliflora var. glandulosa (Torr.) Cockerel] seedlings was continuous throughout a 72-hr period. Approximately 50% of the 2,4,5-T applied to a single leaf was absorbed when 5 to 100 μg were applied. No significant differences were found in the amounts of 2,4,5-T absorbed at 70 and 85 F, but an increase occurred at 100 F after 72 hr. Only slight differences in absorption were found at different humidity levels. Translocation was primarily basipetal from the point of application at 70 F, both acropetal and basipetal at 85 F, and only a short distance acropetal at 100 F. The quantities of 2,4,5-T translocated into untreated tissues at 100 F were less than at 70 and 85 F. The highest concentrations of 2,4,5-T were found in tissues with highest soluble sugar concentrations. From 3 to 27% of the 2,4,5-T absorbed by mesquite leaves was subsequently detected in untreated stem, leaf, and root tissues.

Approximately 80% of the 2,4,5-T absorbed by mesquite leaves was metabolized after 24 hr. Moving the seedlings to a different environment at the time of treatment increased the rate of 2,4,5-T metabolism. Metabolism of 2,4,5-T was completely inhibited at 50 F and a lower rate of metabolism was noted at 100 than at 70 and 85 F. No important differences in metabolism were found at different humidity levels.

Effects of simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) and atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) were observed when applied in connection with 3-amino-1,2,4-triazole (amitrole) to citrus trees. The amitrole had no significant effect. In heavy soil, atrazine toxicity to citrus trees was found during the summer following applications after a period of severe hot dry wind. The leaves became bronzed and dried, growth was checked, dry matter, chlorophyll, and catalase activity of leaves reduced, and their peroxidase activity increased when compared with controls from unsprayed plots; ascorbic acid content of leaves also was affected. Simazine, on the contrary, enhanced growth of trees, total and protein nitrogen and chlorophyll in leaves, did not affect peroxidase, catalase or ascorbic acid, and only slightly depressed dry matter content. In a light soil, probably due to less residual triazines, no toxic effects were observed and untreated controls evinced less growth, lower chlorophyll and nitrogen content of leaves, and higher peroxidase activity than all triazine treatments.

Cotton seedlings emerged normally following applications of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) before or after furrowing for the preplanting irrigation, but 7 to 10 days after emergence stands were sometimes reduced when diuron was applied before furrowing. Stand reductions were most severe when cottonseed were planted at or above the layer of diuron-treated soil. Cotton varieties differed in tolerance to diuron. Preplanting applications controlled annual weeds until mid-season and treated cotton produced normal yields, except where stands were reduced. Fiber properties and boll components of treated cotton were not altered. Content of diuron was highest in young cotton plants. No diuron was found in cottonseed at harvest using an analytical procedure having a sensitivity of 0.1 ppm.

Addition of organic matter reduced the effectiveness of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) to oats in Regina heavy clay soil. At high moisture levels, changes in the relative amounts of clay in the soil did not affect the toxicity of simazine. Toxicity of simazine decreased as the soil moisture level was reduced.

Sesbania (Sesbania exaltata (Raf.) Cory) in soybeans was effectively controlled with wax bars containing 2,4-dichlorophenoxyacetic acid (2,4-D). Bars, 22 in long, were attached horizontally 3 in apart to a tractor-mounted boom and the height was adjusted for it to travel 2 to 3 in above crop plants. Six-pound bars, containing 1 lb of 2,4-D gave better control than bars containing less 2,4-D. Bars made of wax with a melting point of 170 F provided more economical control than bars with waxes of lower melting points. Rate application of wax increased with the size of the weeds treated and with reduced tractor speed. Treatments controlled sesbania without visible injury to soybeans.

The ultraviolet absorption spectra of aqueous dispersions of 2-chloroallyl diethyldithiocarbamate (CDEC) were altered by relatively short periods of exposure to far ultraviolet radiation. Evidence of molecular decomposition also was obtained from solvent partitioning characteristics, gas chromatography, and bioassays. Ultraviolet irradiation of soil surfaces treated with the herbicide decreased its persistence, but no evidence of decomposition was obtained.

Crabgrass (Digitaria spp.) control by different herbicides in field experiments varied from 84 to 100%. These extremes were not significantly different. Greenhouse studies showed that increased moisture content in soils may increase the growth rate of crabgrass seedlings so that they may escape herbicidal injury. Effects of herbicides on root stunting were similar in both dry and wet soils, indicating immobility of the herbicides under these experimental conditions. Competition between mature bluegrass plants and crabgrass seedlings was an important determinant of effective crabgrass control with preemergence herbicides.

A chromatographic procedure for detecting 4-amino-3,5,6-tricholorpicolinic acid (picloram) residue to a sensitivity of approximately 0.05 ppm in soils is described. Picloram is extracted from soil as the free acid and methylated with boron trifluride-methanol reagent. Data indicate that the amount of herbicide which actually reaches the soil may only be 10% of that applied to dense stands of oak. Rainfall was an important factor in determining the movement and persistence of picloram. Picloram was detected to a depth of 24 in within 6 weeks after application. No detectable residues were found in the upper 24 in of soil after one year with rates as high as 8 lb/A.

Low-volatile and high-volatile esters of 2,4-dichlorophenoxyacetic acid (2,4-D) were sprayed on separate pastures at about double the usual rate. Milk from cows grazing these pastures contained from 0.01 to 0.09 ppm 2,4-D during the first 2 days after spraying and lower amounts thereafter. Residues in milk from cows put into the pastures 4 days after spraying were below 0.01 ppm, the practical limit of precision of the method used. Residues of 2,4-D, in or on forage, declined rapidly during the experiment. Almost all the 2,4-D in or on forage was hydrolyzed to the acid form in samples of forage taken within one-half hour after spraying with the butyl ester of 2,4-D, and about 75% after applying the 2-ethylhexyl ester.

A microcoulometric gas chromatographic method with a sensitivity of 0.01 ppm is described for the analysis of 2,4-dichlorophenoxyacetic acid (2,4-D) in milk and forage. The method will analyze 2,4-D as the acid, ester, and bound form from a single sample. Results show the superiority of this method over previous procedures. The formation of 2,4-D ethyl ester from the butyl ester in forage is discussed.

Although selectivity was low, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) gave excellent preemergence weed control when castorbeans (Ricinus communis L.) were planted 2 or 3 in deep. Excellent weed control with little crop injury by 3-amino-2,5-dichlorobenzoic acid (amiben) was provided also and selectivity was not affected by depth of planting.