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.

Foliar applications of the dimethylamine salt of 4(2,4-dichlorophenoxy)butyric acid (2,4-DB) were effective for controlling cocklebur in soybeans. Treatments usually caused crop injury, but treated soybeans often produced higher seed yields than untreated soybeans heavily infested with cocklebur plants. Soybean injury was associated with the mechanical shielding of soybeans by the cocklebur infestation and soil moisture stress at time of treatment. Droughty conditions prior to treatment intensified crop injury and reduced soybeans yields.

A hypothesis that low temperature acts directly on physiological development of coast fiddleneck (Amsinckia intermedia Fisch. and Mey.) by restricting thiamin content, and limiting growth, was investigated. Restoration of normal growth by application of thiamin, made the plant more susceptible to 2,4-dichlorophenoxyacetic acid (2,4-D) at low temperatures.

When vapor losses of isopropyl N-phenylcarbamate (IPC) and isopropyl N-(3-chlorophenyl)carbamate (CIPC) were studied under controlled laboratory conditions using a direct-trap for vapors, IPC proved more volatile than CIPC. Temperature, air-flow rate, moisture, and cation exchange capacity of soil were important factors influencing volatility. Vapor loss increased with increasing air-flow rate and temperature; losses from moist soil decreased as the percent clay, organic matter, or both, and the exchange capacity increased. Vapor losses were negligible from spray applications on dry soil but were sizable from soils at field capacity which were similar to those from soils saturated with moisture. Vapor losses of IPC from granules were much higher than from a surface spray, and CIPC losses were about the same for the granules as from the spray. Covering the soil-applied herbicide with ⅛ to ¼ in of soil was effective in reducing vapor loss.

Applications of disodium methanearsonate (DSMA) killed Johnsongrass foliage in field and greenhouse experiments. Control of regrowth following treatment increased with increasing rates, but there was no indication of translocation to rhizomes. DSMA toxicity did not change in 20 to 80 gpa water, but somewhat less control was obtained in 10 gpa. Addition of a surfactant to spray solutions increased toxicity. Control was not affected by stage of Johnsongrass growth, but observations indicated increased control during droughty conditions. Repeated usage provided seasonal Johnsongrass control equal to that obtained with sodium 2,2-dichloropropionate (dalapon), although more frequent applications were necessary.

Under light grazing, the reproductive capacity of wild carrot (Daucus carota L.) was reduced, but on pastures under heavy grazing, cattle prevented regrowth and seed production of flowering plants. To simulate the effects of cattle grazing, seedlings and flowering plants were clipped at different times during the summer on natural and experimental plots on different soil textures. Plants on fine textured soils were larger in size, regenerated more rapidly, and had a higher survival rate after clipping. The most efficient time for control by a clipping treatment, determined on the basis of prevention of seed production and mortality of plants, was in the latter part of August.

Field dodder (Cuscuta campestris Yunck.) emerged as well in total darkness as in light, but seedlings did not twine about the host. Under the shade of alfalfa, dodder emerged normally, but attachment was reduced more than 90% and delayed 7 to 10 days. Attached dodder shaded by alfalfa did not develop its characteristic golden color, grew very slowly, and was delayed in maturity 3 to 4 weeks.

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.

Herbicides 3-(p-chlorophenyl)-1,1-dimethylurea (monuron); 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine); 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine); 2-methoxy-4,6-bis(isopropylamino-s-triazine (prometone); 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine); and 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) were studied in four soils. The behavior of monuron, propazine, atrazine, and simazine was similar in each soil, while prometryne and prometone exhibited greater interactions with the soils. Phytotoxicity and movement of the herbicides in soil were inversely related to extent of adsorption.

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.

Dimethyl sulfoxide, soil-incorporated at rates of 20 to 240 gpa, prevented the growth of roots and delayed and inhibited the growth of shoots of plants developing from purple nutsedge (Cyperus rotundus L.) tubers for a period of about two months. This effect upon growth occurred only while the tubers and developing plants remained in treated soil; transplanted to untreated soil, subsequent growth of roots and shoots was immediate and normal. The effective soil-residual life of dimethyl sulfoxide was about three months, irrespective of dosage. Dosages of 2½ to 7½ gpa had no effect upon the growth of the nutsedge plants. At 10 and 15 gpa, the inhibitory effect of dimethyl sulfoxide becomes apparent.

The role of corn (Zea mays L.) var. Dixie 18, sorghum (Sorghum vulgare) var. RS 610, and Johnsongrass (Sorghum halepense L.) in dissipation of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) from Norfolk sandy loam was studied in the field and in a pot-culture experiment in the greenhouse. Atrazine residues were determined by both chemical and bio-assay methods. Corn and Johnsongrass field plots had significantly less atrazine remaining in the 0- to 6-in depth than similarly treated fallow plots 1, 2, 3, and 6 months after planting, and the crops were equally effective in dissipating atrazine from soil. Soil in pots cropped with corn, sorghum, or Johnsongrass had significantly less atrazine remaining than in uncropped pots. Uptake by corn, Johnsongrass, and sorghum within 3 months in the pot-culture experiment accounted for losses of approximately 25, 25, and 20%, respectively, of the herbicide initially present. Bio- and chemical assays were equally sensitive methods of determining atrazine in the soil and gave similar results.

The hypothesis that leaf injury from applications of fenuron (3-phenyl-1,1-dimethylurea) is a direct result of a lack of photosynthate did not explain the results of experiments with seedlings of shrub live oak (Quercus turbinella Greene) supplied with an acorn food reserve supplemented with glucose solution, and with seedlings whose acorns were excised or left attached to the seedlings. An alternate hypothesis is offered: acute leaf injury from phenylurea treatment is due to one or more components of the electron transport chain, between the chlorophyll b pigment system and the reduction of triphosphopyridine nucleotide, which are left in a toxic oxidized state as a result of the phenylurea block in the oxygen-liberating system. Evidence also favors the above interpretation rather than the idea that toxicity results from the accumulation of a toxic oxidized product on the oxygen-liberating pathway. Although leaf injury appears to be due to toxic components of the inhibited photosynthetic apparatus, the ultimate cause of death of the entire plant is starvation.

Besides its effect on photosynthesis, fenuron at high concentrations also causes inhibition of root growth.

The loss of 2-chloroallyl diethyldithiocarbamate (CDEC) from the dry surface of four soils was followed over a 24-hr period by spectrophotometric procedures. As the temperature was in creased from 31 C to 44 C and to 54 C, average losses from all soils increased from 33 to 47 to 54%, respectively. There was relatively little difference in rates of loss from the different soils. Loss at 44 C at low (20%) and moderate (65%) relative humidity generally was similar in magnitude. Losses from a wet soil surface at 44 C were much more rapid than from a dry soil.

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.

Following root application of a selective rate of 3-amino-2,5-dichlorobenzoic acid-C14 (amiben-C14), the translocation of radioactivity from roots to shoots was greater in pigweed (Amaranthus retroflexus L.), a susceptible plant, than in soybeans, a resistant one. Most of the radioactivity extracted from soybean and pigweed plants was present as conjugates of amiben-C14. The conjugate extracted from soybean was chromatographically identical with an N-glycoside prepared from glucose and amiben. In soybean plants, 3-amino-2,5-dichlorobenzoic acid also was converted to N-glycosylamiben.

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.

Germination of wild carrot (Daucus carota L.) was not confined to any season but was correlated with abundant soil moisture in field studies. In laboratory studies, germination percentage for any seed lot increased with time as dormancy was overcome. Further, the germination was not clearly correlated with seed weight, light, or pH, but temperature and the availability of water were clearly significant. Dormancy was due to the endosperm which surrounds the embryo. When part of the endosperm covering the tip of the radicle was digested or broken off, germination was increased nearly to the potential for a given lot of seed

Results were based on plant response with light levels in energy units, in accord with use of the spectrum by plants. Dry weight yields of control plants, and reductions of yields by 2,4-dichlorophenoxyacetic acid (2,4-D) below those of control plants were greatest in red light, followed by pink, yellow, white, green, and blue light, in that order. Sucrose mixed with 2,4-D or applied alone to plants altered the combined light-herbicide effect but little. Differences in concentration of 2,4-D affected respiration more than photosynthesis, as measured by CO2 exchange under different light qualities. In spectral effects, pink light caused greatest reduction of photosynthesis by 2,4-D at 500 ppm, while greatest promotion of respiration occurred under red light with 2,4-D at 1000 ppm.

The herbicide 2,6-dichlorobenzonitrile (dichlobenil) was quite persistent in cranberry bogs. The chemical was not readily leached downward in the soil nor carried from the bog by flood water but was recovered primarily in the upper 4 in of the soil. Chemical residue analysis demonstrated a greater quantity of herbicide was present than indicated by a bio-assay test. Most of the herbicide is believed to be held ineffective by the organic matter in the soil.