Eurasian watermilfoil (Myriophyllum spicatum L.), a submersed aquatic weed, has seriously interfered with many water uses in the TVA reservoirs. More than 150 test plots were treated with 34 herbicides from 1960 through 1965. More effective results were obtained with granular preparations of butoxyethanol ester, 2-ethyl hexanol ester, and propylene glycol butyl ether ester of 2,4-dichlorophenoxyacetic acid (2,4-D) and liquid preparations of propylene glycol butyl ether ester and potassium salt of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex).

The two most effective control methods found from field tests were (a) lowering the lake levels enough to permit complete drying of stems and root crowns and (b) applying butoxyethanol ester of 2,4-D in a 20% granular form. Applications of this herbicide to about 3,700 acres at rates of 20 and 40 lb/A gave results that varied from excellent control in protected embayments to poor control in moving water on these large impoundments.

Complete control of annual bluegrass (Poa annua L.) at all levels of P and at both planting dates was obtained with a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 2 lb/A. For both planting dates, high levels of P reduced the effectiveness of both calcium arsenate (CaAs) and to a small degree dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA). On a plant count basis, O-(2,4-dichlorophenyl)O-methyl isopropylphosphoramidothioate (DMPA) was more effective than N-(2-mercaptoethyl) benzenesulfonamide S-(O,O,-diisopropyl phosphorodithioate) (bensulide) for the control of annual bluegrass.

In the field, injury to bentgrasses (Agrostis palustris Huds.) from preemergence herbicides generally was specific to one or two varieties. Washington bentgrass was severely injured from a 12-lb/A application of 1-(2-methylcyclohexyl)-3-phenylurea (siduron).

A quantitative colorimetric procedure was developed for the determination of N-glucosyl amiben in tissue sections of etiolated seedlings. N-glucosyl amiben biosynthesis in soybean hypocotyl sections was heat labile, sensitive to freezing and thawing, unaffected under anaerobic conditions, dependent on amiben concentration, and proportional to tissue section concentration. The formation of N-glucosyl amiben in soybean hypocotyl sections was greatest between pH 6.3 and pH 7.3 and was inhibited by NaF, HgCl2, iodoacetate, iodoacetamide, and N-ethylmaleimide but not by NaCN or NaN3. On a specific activity basis, sugar beet seedling, soybean cotyledon, and soybean hypocotyl tissue sections were the most active tissues studied in the biosynthesis of N-glucosyl amiben.

Aerial herbicide treatments were made on a native stand of short-leaf pine (Pinus echinata Mill.) heavily infested with noncommercial oak (Quercus sp.), hickory (Carya sp.), and associated species in southeastern Oklahoma from 1957 through 1960. Two formulations of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were applied in May and September at 1½ lb/A annually in one, two, and three applications with the later two made a year apart. The most diameter growth for all sizes of pine measured occurred following May treatments. Late May aerial applications also were made with 2-(2,4-dichlorophenoxy) propionic acid (dichloroprop) and 2-(2,4,5-trichlorophenoxy) propionic acid (silvex). Silvex reduced pine cone development, seed fill, and germination.

Native grass growth was increased twice following good weed tree control. However, where dense short-leaf pine seedlings developed, the native grasses were smothered and volume of herbage decreased.

The dimethylamine salt and isopropyl and isooctyl ester formulations of 2,4-dichlorophenoxyacetic acid (2,4-D) were applied at 0, ½, 1, 2, and 4 lb/A 21, 14, and 7 days before harvesting Bison hard red winter wheat. Treatment effects on yield, chemical composition, or milling and baking properties of the grain were either nil or of no practical significance. When treated with ½ or 1 lb/A, rates generally recommended for farm use, 2,4-D residues in the grain ranged from 0.04 to 0.27 ppm. As rates of the three formulations of 2,4-D were increased from ½ to 4 lb/A, increasing amounts of 2,4-D residues occurred in the grain and reached a maximum of 1.8 ppm when the isopropyl ester of 2,4-D was applied at 4 lb/A 14 days before harvest. Grain from plots treated 21 days before harvest had less 2,4-D residue than grain from plots treated 14 and 7 days before harvest.

Several herbicides were used for control of weeds in Jersey Orange sweet potato plantings on a sandy loam soil at Hammonton, New Jersey, during 1960, 1961, and 1962. The treatments were applied preemergence to the weeds at transplanting of the crop. Data included crop injury scores, level of weed control, effects on yield, influence on internal root color and flavor, and effects on sprouting.

Excellent control of germinating annual weeds was obtained with 3-amino-2,5-dichlorobenzoic acid (amiben), 2,6-dichlorobenzonitrile (dichlobenil), N,N-dimethyl-2,2-diphenylacetamide (diphenamid), and dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA). These herbicides had no adverse effects on yield, quality factors, or growth.

The toxicity, adsorption, and leaching of four herbicides in different soils were determined by a method based on a sensitive root bio-assay which appeared suitable for herbicides affecting root growth. The rate of leaching of the herbicides was determined by measuring the herbicidal effect of the leachate obtained from three heights of soil columns. The same bio-assay was utilized for testing the extent of inactivation of herbicides due to adsorption by soil. In this case, mixtures of various rates of soil with silica sand were used as cultures for the bio-assay.

Under controlled conditions in a growth chamber, emergence of tumblegrass (Schedonnardus paniculatus (Nutt.) Trel.), redroot pigweed (Amaranthus retroflexus L.), and barnyardgrass (Echinochloa crusgalli (L.) Beauv.) was best with an 8-hr night temperature of 65 F and a 16-hr day temperature of 80 F. Other temperature ranges, in order of decreasing effectiveness in stimulating emergence, were 80–95, 50–65, and 35–50 F. Best emergence occurred at the ½-in depth of planting followed by 14, 1, 2, and 4 in. Barnyardgrass was the only weed that emerged appreciably from the 4-in depth. Average emergence was better on a coarse-textured soil than on a fine-textured soil. Under dry soil conditions, emergence was reduced by soil crusting.

To evaluate the effect of different soil moisture levels on the phytotoxicity of soil applications of arsenic trioxide (As2O3), water and alcohol extractable soil arsenic (As) data were related to the growth and development of 4-month-old Monterey pine (Pinus radiata D. Don.) in greenhouse soil cultures. Also, various rates of As2O3 and water were applied to the surface of soil columns to determine the effective penetration of soluble As. Under normal moisture regime, 8000 lb/A of As2O3 were required for high phytotoxicity on a Chenango silt loam, with excessive moisture resulting in an increase in this phytotoxic effect. With water and alcohol extraction procedures, an adequate range of values was obtained in relation to the total As2O3 rates and plant responses. Lethal concentrations of As in the soil columns were limited to the surface 3 in depth in the silt loam.

Rhizome differentiation in yellow nutsedge (Cyperus esculentus L.), cultured under 12½, 14, and 15½-hr photoperiods, 21–16, 27–21, and 33–27 C temperatures (day and night, respectively), Hoagland solutions of 1/32, 1/8, and 1/2 strength nitrogen (N), and 0, 10, and 1000 ppm gibberellin (GA), was investigated in controlled-environment chambers.

High levels of N, long photoperiods, and high levels of GA at the shortest photoperiods inhibited tuberization whereas high temperatures at the lowest N level favored tuberization. Shoot formation was promoted by high levels of N, long photoperiods, and high temperatures under 12½ and 14-hr photoperiods while GA had a retarding effect. The higher levels of N, temperature, and GA decreased carbohydrate level whereas the longer photoperiods increased it.

It may be concluded that tuberization is not only the result of surplus carbohydrates in the plant but is controlled also by some GA-like substances regulated in the plant under specific conditions of photoperiod and temperature.

Preemergence herbicides were applied to lawn turf on a loam soil in April, 1963. Polychlorodicyclopentadiene isomers, N-2-mercaptoethyl)benzenesulfonamide (bensulide), calcium arsenate, 1,2,4,5,6,7,8,8a-octachloro-4,7-methano-3a,4,7,7a-tetrahydroindane (chlordane), dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) 0-(2, 4-dichlorophenyl)-0-methyl isopropylphosphoramidothioate (DMPA) and 2,6-di-tert-butyl-p-tolyl-methylcarbamate (terbutol) were included. Soil of the respective plots were sampled from 0 to 2- and 2 to 4-in depths in December. These soils samples were used for planting plugs of mature Merion Kentucky bluegrass. The cultures were grown for 18 days in the greenhouse. Twenty-three in of rain had fallen between the treatment and sampling dates. Yet root growth was seriously reduced in the soil from the 0 to 2-in depth that had received terbutol and bensulide. Several chemicals gave significant reductions in topgrowth. Preemergence herbicide residues had sufficient influence on Kentucky bluegrass type lawn turf to justify specific study of each chemical with regard to this factor before widespread use.

A series of three experiments was conducted from 1951 to 1963 for the control of western snowberry (Symphoricarpos occidentalis Hook.) in southern Nebraska. Western snowberry was best controlled with 2,4-dichlorophenoxyacetic acid (2,4-D) when sprayed in early full foliage. Timeliness of herbicide application was considered the most important factor in a control program. Excellent control was obtained with 1 to 2 lb/A of the isopropyl ester of 2,4-D in all studies. The triethanol amine salt of 2,4-D was less effective. A 1:1 mixture of 2,4-D + 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at 1 and 2 lb/A, 2,3,6-trichlorobenzoic acid (2,3,6-TBA) at 1 and 2 lb/A, and 3-amino-1,2,4-triazole (amitrole) at 2 and 4 lb/A were not as effective for western snowberry control as 2,4-D. Mowing was an ineffective method of control.

Quantitative measurements were made by cucumber root bioassay of 2,4-dichlorophenoxyacetic acid (2,4-D) contained in washoff (water-soil mixture) from cultivated fallow Cecil sandy loam soil. Formulations of 2,4-D used included iso-octyl and propylene glycol butyl ether esters and an alkanolamine salt of the ethanol and isopropanol series. Simulated rainfall intensities and storm durations used represented storm frequencies of 1, 10, 80, and greater than 100 years. The 2,4-D applied at rates of 2.2 or 4.4 lb/A was assayed in washoff and as residue in the soil. Concentrations of 2,4-D in washoff were positively correlated with the rate applied, were greatest early in each storm, and decreased with duration of the storm. The iso-octyl and butyl ether ester formulations of 2,4-D were far more susceptible to removal in washoff than the amine salt. When the amine salt was used, 2,4-D concentrations in washoff were less than 1 ppm, even in the early stages of runoff, whereas concentrations as high as 4.2 ppm were measured using an iso-octyl ester formulation of 2,4-D. When a direct comparison was made between the butyl ether ester and amine salt forms of 2,4-D, ester or amine losses were respectively, 13 and 4% following a 1-year frequency storm and 26 and 5% following a 100-year frequency storm. Soil bioassays showed that most of the 2,4-D remained in the surface 3 in of soil.

A 4-year field study was conducted to determine losses and gains in alfalfa production and utilization due to direct competition of various densities of Canada thistle (Cirsium arvense (L.) Scop.) and their control. Regardless of initial Canada thistle density, within 4 years all stands under no control approached one plant/sq ft. Mowing after each grazing period for 4 years almost eliminated Canada thistle. Throughout the study, the rate of alfalfa stand reduction was the same under mowing treatment regardless of Canada thistle density. Mowing increased alfalfa production 6.2 T/A in 4 years over no control in plots having initial Canada thistle stands of two plants/sq ft. The production loss due to Canada thistle stands of two plants/sq ft was 7.4 T of alfalfa for a 4-year period. Alfalfa consumption was reduced 4.5 T/A.

Preliminary observations indicate that tobacco is extremely sensitive to 4-amino-3,5,6-trichloropicolinic acid (picloram). This study was conducted to determine the effect of time and rate of treatment on tobacco yield, quality, dollars per acre, and the effect on chemical constituents in the tobacco. Results indicated that picloram remaining in the soil as a residue at rates of 5 g/A and above can cause serious damage to tobacco. A broadcast spray applied shortly after setting the tobacco in the field was most injurious to tobacco. One-half g/A at this time reduced dollars per acre by about 50%. The tobacco plant gained tolerance to 2.5 g/A by the time it was 24 in tall.

Treatments made when the tobacco was 24 in tall and also when treated after topping controlled suckers at rates of 0.5 and also at 2.5 g/A.

Results of studies with the herbicide 1-(3-chloro-4-methylphenyl)-3-methyl-2-pyrrolidinone (hereinafter referred to as BV-207) suggest that it interferes appreciably with photosynthesis. A concentration of 10-4 M of BV-207 almost completely inhibited fixation of labelled carbon dioxide by leaf disks of various plants. In addition, carbohydrates protected plants from the phytotoxic action of the chemical. BV-207 was considerably more toxic when plants received light after application of the herbicide, compared with those held in the dark. On the other hand, root growth was inhibited only slightly by BV-207.

Tracer studies employing 2,2-dichloropropionic acid (dalapon)-2-C14 and -Cl36 were conducted on barley (Hordeum vulgare L.), bean (Phaseolus vulgaris L.), and three hypostomatous species—zebrina (Zebrina pendula Schnizl.), coleus (Coleus blumei Benth.), and nasturtium (Trapoelum majus L.). Count data and radioautographic evidence showed that greater amounts of dalapon were absorbed and translocated at high (88 ± 3%) than medium (60 ± 5%) or low (28 ± 3%) post-treatment relative humidity (herein called R.H.). Also, greater uptake and translocation of C14 occurred in bean at 43 ± 1 C than at 26 ± 1 C post-treatment temperature, with constant R.H. and light conditions. Rate of droplet drying, and stomatal distribution and behavior, apparently contributed to the R.H. effect. Droplets dried less rapidly at high than at low R.H., thus prolonging the period of effective absorption. At low R.H., periodic rewetting of the droplet area enhanced absorption and translocation but never to the extent achieved with high ambient R.H. (in growth chambers) or in saturated atmosphere (polyethylene bagging in the greenhouse). High R.H. (95 ± 3%) favored stomatal opening in zebrina, and uptake of dalapon was greater through the abaxial than adaxial surface of leaf disks of zebrina, coleus, and nasturtium. Rewetting of droplets or high ambient R. H., however, promoted uptake through astomatous as well as stomated surfaces. Absorption and translocation were markedly greater in bean plants grown at 95 ± 3% R.H. than at 28 ± 3% R.H., both treated under high R.H. conditions. Thus cuticle hydration and ontogeny also were implicated in the R.H. phenomenon. Several solution additives also were studied in an attempt to substitute for the R.H. effect. At low R.H., a surfactant (X-77) markedly enhanced uptake of dalapon in bean, glycerol (a humectant) and hexadecanol (a filming agent) were less advantageous, and Plyac (a sticker-spreader) decreased penetration. Results of these studies aid in explaining the greater toxicity of dalapon in regions of high R.H. and, conversely, its sometimes erratic performance in drier climates. The results also confirm the distribution and accumulation patterns of dalapon absorbed by plants and the usefulness of an effective spray adjuvant in promoting foliar absorption.

In field experiments, corn (Zea mays var. Dixie 18) and Johnsongrass (Sorghum halepense) seeds were planted in Norfolk sandy loam soil and treated preemergence with 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) at 0, 2, 4, and 16 lb/A. In growth chamber studies, corn seeds were planted in flats of Independence loamy fine sand and treated pereemergence with atrazine at 0, 2, and 4 lb/A. In nutrient culture studies, corn was treated with 0, 2, 4, and 8 ppmw atrazine.

Treated plants of all species and rates tested usually were smaller than untreated plants and contained higher nitrogen percentages. Corn and Johnsongrass plants treated with high rates of atrazine always contained less nitrogen (mg/plant) than untreated plants. Atrazine-treated corn plants contained higher percentages of both 80% ethanol soluble and insoluble nitrogen than the checks. Percentage increases in both fractions were proportional to the rate of atrazine treatment. Nitrate percentages also were increased, but free ammonia content was not significantly affected.

Satisfactory selectivity of 4-chloro-2-butynyl m-chlorocarbanilate (barban) for the control of wild oats (Avena fatua L.) in spring wheat was obtained when it was applied from 4 to 14 days after emergence of wild oats. Following this period, the effectiveness and selectivity declined rapidly. Depending on the season, this period of maximum efficiency represented the following growth stages of wild oats; 1 to 3-leaf stage in 1960, 1½ to 3½-leaf stage in 1961, and 1½ to 2½-leaf stage in 1962. Injury to wheat was most pronounced during a period beginning about 15 days after crop emergence and continuing for several weeks. This pattern of wild oat control and wheat susceptibility was virtually identical over the 3-year period even though growing conditions varied considerably. This suggests that days after emergence may be at least as reliable as leaf stages as an index for the proper timing of barban treatments and would be more easily determined under practical field conditions. If leaf stages are used, then spraying should not be recommended later than 2½-leaf stage, since in some years, wild oats will have reached resistant stages. Furthermore, it may be desirable to apply barban early, perhaps even before all the plants are fully in the 2½-leaf stage. When wild oats reach the 2-leaf stage, it may be too late, at least in years of abundant moisture.

The herbicidal activity of potassium azide and calcium cyanamid, applied singly and in combination, was evaluated in greenhouse and field experiments. In the greenhouse, the combinations were synergistic against several plant species including yellow nutsedge (Cyperus esculentus L.) and crabgrass (Digitaria sanguinalis (L.) Scop). The combinations also were synergistic in two field experiments at different locations. In the field, the combinations reduced the number of weed seeds germinating from treated soil over a 6-month period; potassium azide or calcium cyanamid applied singly were not effective. In the laboratory, calcium cyanamid reduced the rate of disappearance of potassium azide from the soil.