Greenhouse evaluation of 30 s-triazine compounds indicated that several of them were suitable for pre-emergence weed control in Lee soybeans. The s-triazines least toxic to soybeans generally contained either methoxy or methylmercapto substituents but most of these were highly toxic to crabgrass (Digitaria sanguinalis (L.) Scop.). Soybeans were more tolerant to ethylamino substituted s-triazines than to isopropylamino derivatives. Chloro derivatives were generally toxic to soybeans. Proplyamino, allylamino, methoxypropylamino, ethoxy, trichloromethyl, and amido substitutions had much less effect on soybean selectivity than those previously mentioned.

Field evaluation of several s-triazines, preemergence, confirmed the tolerance of soybeans to 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne), 2-ethylamino-4-isopropylamino-6-methylmercapto-s-triazine (ametryne), and 2-isopropylamino-4-methylamino-6-methylmercapto-s-triazine (norametryne) at rates that provided adequate weed control.

Ninety-one herbicides and experimental compounds were evaluated for herbicidal activity on submersed aquatic weeds, Potamogeton pectinatus L. and P. nodosus Poir. Twenty-one of the compounds tested showed some phytotoxicity at 20 lb/A. The other compounds were completely inactive. 2,3,6-Trichlorophenylacetic acid (fenac) and 2,6-dichlorobenzonitrile (dichlobenil), showed outstanding activity with good persistence in water-saturated soil. Fenac and 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), were tested in field trials in an irrigation canal in eastern Wyoming. The sodium salt and amide of fenac did not give adequate weed control at 5 lb/A. Spring applications of herbicides did not perform as well as fall ones. Mechanical incorporation of herbicides improved some results, but was of doubtful value.

The addition of a combination of methyl cellulose, sodium acetate and an alkyl aryl sodium sulfonate (sodium petroleum sulfonate) to spray solutions increased the toxicity of 2,2-dichloropropionic acid (dalapon) to oats and Cynodon dactylon L. The most effective combination tested on oats in the laboratory was 2.25% methyl cellulose, 1.75% sodium acetate, and 0.8% of an alkyl aryl sodium sulfonate. Lower concentrations of the three materials, combinations of any two of these additives, or any one added alone were less effective. Under field conditions, the response of Cynodon dactylon L. to dalapon was more rapid, control was more uniform and regrowth slower when dalapon sprays contained the three additives. Methyl cellulose increased and maintained the spray load on the grass foliage. Alkyl aryl sodium sulfonate probably increased penetration of dalapon. Sodium acetate increased the toxicity of the spray.

The interaction of soil applied phosphorus and soil applied herbicides was investigated in field, greenhouse and controlled environment chamber studies. A previously reported diuron-phosphorus interaction could not be repeated under all conditions studied. Amitrole was consistently more toxic to plants grown under high phosphorus levels than under low phosphorus conditions. The phytotoxicity of ten other herbicides was not influenced by the phosphorus content of the soil.

Application of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) was effective in controlling quackgrass (Agropyron repens) in fields planted to corn. Corn yields were greatly improved by the treatment. Most favorable dates of application were in the fall or in the early spring before planting. Applications after corn planting were much less effective. Favorable rates of application were 2 to 4 lb/A. Rates lower than 2 lb/A were not as effective and rates over 8 lb/A were not required. Atrazine and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) were generally superior to other triazine analogues used. Greater solubility and greater activity as a foliar spray favors use of atrazine for control of quackgrass.

Rates of evaporation of dalapon acid and four low-volatile esters of dalapon from open dishes at 38C. in pounds per acre per hour, determined gravimetrically, were dalapon acid, 180; propyleneglycol bis ester, 27; diethyleneglycol bis ester, 1.6; dipropyleneglycol bis ester, 0.83; and triethyleneglycol bis ester, 0.61. Foliar applications on an acid equivalent basis were phytotoxic to seedling oats in the increasing order of propyleneglycol bis ester, acid, dipropyleneglycol bis ester, diethyleneglycol bis ester, sodium salt, and tripropyleneglycol bis ester. Relative phytotoxicities were not altered by subjecting plants to rapid drying after spraying. These compounds did not differ significantly in phytotoxicity when added to the rooting medium of germinating oat plants. The triethyleneglycol bis ester, and possibly other esters of dalapon, may offer practical advantages as herbicides other than those related to volatility.

Measurements of C14-labeled 2,4,5-trichlorophenoxyacetic acid absorbed and translocated from treated leaves of blackjack oak (Quercus marilandica Muenchh.) showed that absorption and translocation were highest in early spring and decreased during May and June, so that there was a minimum at about the first of July. Absorption and translocation increased during July, August, and September. Measurements of soil moisture did not reveal a correlation of water stress and translocation rates. Extensive variations in the respiration rates of the leaf tissue occurred during the growing season. The trends in respiration rates generally paralled the trends in translocation rates.

The effect of fully-saturated bicyclic and partially-saturated tricyclic dimethylureas and dimethylthioureas on the photolytic activity (Hill reaction) of chloroplasts isolated from turnip greens (Brassica spp.) was studied. Photochemical activity was measured potentiometrically with ferricyanide as the electron acceptor. Chemicals tested were 3-[5-(3a,4,5,6,7,7a-hexahydro-4,7-methanoindenyl)]-1,1-dimethylurea; 3-(chloro-2-norbornyl)-1,1-dimethylurea; 1,1-dimethyl-3-(2-norbornyl)urea; and the 3 corresponding thioureas. Concentrations of the 3 polycyclic ureas required to inhibit the Hill reaction by 50 percent (I50) were respectively 4.0 × 10-6 M, 1.2 × 10-5 M, and 6.6 × 10-5 M. The thioureas were not very inhibitory to the Hill reaction; consequently, their I50 values were not determined. The fully or partially-saturated polycyclic dimethylureas were weaker inhibitors of the Hill reaction than the phenyldimethylureas. The decreased inhibitory activity of the polycyclic ureas was attributed to increased lipophilic properties, unfavorable spatial configurations, and lack of resonance interaction between the ring system and the imino nitrogen.

Long-term compensation points in waterstargrass (Heteranthera dubia (Jacq.) Mac M), coontail (Ceratophyllum demersum L.), and duckweed (Lemna minor L.) were near 2–3% full sunlight during a 28-day period. Fresh weight of H. dubia increased as temperature increased from 15 to 30 C and as light intensity increased from 110 to 1000 foot-candles. Fresh weight of C. demersum increased as temperature increased above 20 C and as light intensity increased from 120 to 550 foot-candles. The L. minor strain used in this experiment was not temperature-dependent and increased in fresh weight and frond number at 25 and 30 C as light intensity increased from 77 to 550 foot-candles.

Foliar absorption of 2,4-D-C14 was rapid in both species. Cotton decarboxylated the side chain of 2,4-D several times faster than sorghum. Both species released C14O2 faster from the carboxyl than from the methylene position. Cotton slowly converted 2,4-D to a chromatographically different material in young leaves and bolls. Sorghum rapidly converted 2,4-D to a product different from 2,4-D and the 2,4-D-complex in cotton. After cotton recovered from 2,4-D-treatment, the regulator could not be detected in subsequent vegetative or reproductive growth.

Field studies at three locations across Nebraska showed that 2,3,6-trichlorobenzoic acid (2,3,6-TBA) leached readily into the soil profile. The herbicide was lost from the surface soil much more readily in central and western Nebraska than in eastern Nebraska even though rainfall was about twice as much at the last location. Volatilization was suggested as a possible reason for this loss of 2,3,6-TBA. There was a definite, but not complete, loss of 2,3,6-TBA from the three soil profiles between May 1960 and September 1961. Soybeans proved to be an acceptable bioassay plant for this herbicide in soil at 2,3,6-TBA concentrations of ½ to 2 ppmw.

For many years the disparity in values placed by different people on naturally growing plant species in both non-cropland such as in rights-of-way and in crop fields has been apparent. For example, agencies responsible for highway maintenance have preferred to destroy most growths of woody species located on roadsides because they were an obstacle to snow removal or ditch drainage. Some agriculturists have advanced land-use practices aimed at eliminating all non-crop vegetative growths whether herbaceous or woody located anywhere on the farm. Conversely, wildlife managers not only have stressed the importance of leaving all non-crop vegetation but have advocated the planting of more shrub species.

Of the grasses studied over a 3-year period, Alta tall fescue (Festuca arundinacea) was most competitive and Troy bluegrass (Poa pratensis L.) least competitive with Canada thistle (Cirsium arvense). Ladino white clover was more competitive than birdsfoot trefoil (Lotus corniculatus) when present in full stands. Winter-killing of Ladino clover (Trifolium repens L.) resulted in an increase in Canada thistle, particularly at low irrigation levels. Irrigation favored an increase in Canada thistle numbers in the year the grass stands were established. In the next two years thistle numbers declined more rapidly on irrigated than on non-irrigated plots. High rates of nitrogen increased the competitive ability of the grasses.

Dalapon (2,2-dichloropropionic acid) was applied to a predominantly medusahead (Elymus caput-medusae L.) community at rates of 1, 2, 3, 4, and 5 lb/A and at four stages of growth. Low rates of dalapon gave better control when applied at early growth stages than the same rates applied later. Reduction in total ground cover was less from December and February applications than from March applications.

Dalapon at 3 lb/A applied 30 days after emergence gave 100% kill of medusahead. Two lb/A gave 96% or better control when applied during the vegetative stage (December, February, March). Both 2 and 3 lb/A applied in December, and 2 lb/A in February left a favorable balance of species among the remaining forage plants.

Rough pigweed (Amaranthus retroflexus L.) on the average emerged 2 days earlier than yellow foxtail (Setaria glauca (L.) Beauv.) The heading and maturity of both weeds seeded in corn was delayed for 3–4 days. The interval between emergence and maturity decreased progressively as seeding dates were delayed. The tallest plants and the highest yields were produced from the early spring seedings. Competition from corn depressed yields of both weeds more than their heights. Height and yield of foxtail seeded during July were most affected. In later seedings foxtail tolerated corn competition much better than pigweed.

Orchardgrass (Dactylic glomerata L.) and Kentucky bluegrass (Poa pratensis L.) were used as test species to study the phytotoxicity of mixtures of 2,2-dichloropropionic acid (dalapon) and dimethylarsinic acid (cacodylic acid). A technique involving ED50 values, a shortened graphic procedure, and probit transformations was developed. Mixtures in which cacodylic acid was in excess indicated synergistic effects on bluegrass and additive effects on orchardgrass. Dalapon in excess in the mixtures appeared to have had an antagonistic effect on cacodylic acid. Orchardgrass was more tolerant to cacodylic acid than bluegrass.

The fate of 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) in Wymore silty clay loam soil at Lincoln, Bridgeport loam soil at North Platte, and Rosebud loam soil at Alliance, Nebraska, was followed during a 16-month period. Oats grown for 40 days in the field as a bioassay crop showed that simazine and atrazine were less phytotoxic in the finer textured soil where the rainfall was highest. Soybean bioassays in soil from different horizons showed a higher concentration of monuron remaining in the 0- to 3-inch soil horizons than of simazine or atrazine. There was a marked decrease of monuron phytotoxicity in the 3- to 18-inch soil layer 16 months after as compared to 4 months after the herbicide application. Atrazine showed the greatest leaching of the three herbicides in this study.

Development was followed in Connecticut and Maryland. Germination of yellow foxtail (Setaria lutescens (Weigel) F. T. Hubb. occurred over a long time period. Tillering of the developing plants was affected by spacing between plants and location. The average number of tillers in Maryland was 75 for plants spaced 12 in. apart and 26 for plants spaced 2 in. apart. In the greenhouse under short day conditions seed heads were readily produced. Under continuous light no seed heads formed. Giant foxtail (S. Faberii Herrm.) followed a similar growth pattern but the plants were larger and formed fewer tillers. Growth of both species was severely affected by shading. Both species rooted from cuttings.

The butoxyethanol and propylene glycol butyl esters of 2,4-dichlorophenoxyacetic acid (2,4-D) were applied to and recovered from the leaf surfaces of garden bean and corn plants. Both the acid and the ester of 2,4-D were recovered, indicating that hydrolysis of the esters had occurred. The acid and esters of 2,4-D were also found in both leaves and stems of the bean plants, indicating that further hydrolysis had occurred within the plants. Bean plant homogenates incubated with 2,4-D esters yielded 2,4-D acid. The root exudate from corn plants treated with 2,4-D butoxyethanol ester showed the presence of both acid and ester.

The toxicity to bluegill sunfish (Lepomis macrochirus, Rafinesque) of 3 to 21 commercial formulations of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2-(2,4-dichlorophenoxy)propionic acid [2-(2,4-DP)], and 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) was determined. The variations among formulations of the same herbicide were much greater than those among different herbicides. Variations in toxicity of a single formulation were also noted. Formulations of each herbicide were reported as either safe or unsafe for aquatic applications. Amine salts were generally less toxic to fish than esters. The formulation selected for use should be assayed prior to field application, using the receiving water.