A new technique designed for the study of various modes of weed competition has been developed and tested. It applies to almost all environmental conditions as they affect plant growth. The technique is adaptable to single factors and multiple factors in almost any combination. The only major restriction imposed by present dimensions is that only early competition can be studied.

The uniformity of seed used in closely controlled competition studies is extremely important. Heavy seeds of redroot pigweed (Amaranthus retroflexus L.) produced plants that brought about earlier and more intense shading than plants from light redroot pigweed seed. Applying an aluminized Mylar reflective surface on the inside of the aerial portion of the competition box increased the growth rate and development of species and shortened the time interval for experiments by 10 days.

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.

Thiobacillus thioparus, Azotobacter chroococcum, Rhizobium leguminosarum, Aspergillus niger, Paramecium caudatum, Colpidium sp., and a mixed culture of soil ciliates were not adversely influenced nor stimulated by the presence of dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA). Soil from plots treated 7 years at 5.0 ppm showed no accumulation of DCPA. Plate counts of actinomyces, bacteria, and molds from field and laboratory-treated soils showed no adverse effect. A mixed culture of soil algae and fungi grew significantly more in the presence of DCPA.

Water lettuce (Pistia stratiotes L.) was susceptible to applications of 6,7-dihydrodipyrido(1,2-a:2’,1′-c)pyrazidiinium salt (diquat). The most satisfactory rates of application were 1.0 to 1.5 lb/A of diquat. The addition of a surfactant did not increase the effectiveness of diquat. Several other chemicals gave unsatisfactory control of water lettuce.

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).

The selective properties of 5-amino-4-chloro-2-phenyl-3-(2H)-pyridazinone (pyrazon), a new herbicide for the control of weeds in sugar beets, were investigated. Common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and green and yellow foxtail (Setaria viridis (L.) Beauv. and S. glauca (L.) Beauv.) represented about 77% of the weeds emerging and developing with beets. The preemergence rate of 4 to 5 lb/A pyrazon satisfactorily controlled the two broadleaf weed species but was marginal in controlling foxtail. At 6 and 7½ lb/A, beet stands were reduced; however, because of the standard practice of overseeding, normal stands were possible and yields of roots and extractable sugar were unaffected. Preemergence applications of aqueous suspensions of pyrazon were more satisfactory than postemergence. The addition of miscible non-phytotoxic oils or adjuvants to aqueous mixtures greatly improved the postemergence activity of pyrazon. In spite of the occasional temporary beet injury, beets in the two to four-leaf stage seemed relatively tolerant to postemergence treatments. Control was excellent when weeds were treated in the seedling stage (i.e. between cotyledon and four true leaves).

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.

Experiments were conducted to determine adsorption of methanearsonate by soils, soil separates, and reference clay minerals from solutions of disodium methanearsonate (DSMA), effects of soil type and pH on the leaching of surface-applied DSMA, and effects of soil type and added organic matter on the oxidation of the methyl carbon of methanearsonate.

Adsorption of methanearsonate by kaolinite and vermiculite increased with increasing concentration of DSMA in the equilibrium solution. Kaolinite and limonite adsorbed much more methanearsonate than vermiculite and montmorillonite. The clay fraction of Augusta silt loam adsorbed more methanearsonate than did the sand and silt fractions. Adsorption by whole soils was related generally to their clay contents.

Leaching with 20 successive 1-in increments of water removed 52% of surface-applied methanearsonate from Norfolk loamy sand. Rates of movement of DSMA in Norfolk loamy sand did not differ at three pH levels. About one-half of the applied methanearsonate remained in the surface inch of Decatur clay loam and none was leached below 6 in.

Oxidation of the methyl carbon of methanearsonate was associated with oxidation of soil organic matter in each soil. In three of the soils, there was no evidence of microbiological adaptation to methanearsonate. In Norfolk loamy sand, however, increasing decomposition of methanearsonate relative to soil organic matter occurred with time of incubation. Decomposition of added plant material in this soil enhanced the oxidation of methanearsonate.

Sixteen field tests conducted over 12 years showed that, under the soil and climatic conditions prevailing in the Peace River region of western Canada, application of maximum rates of 20 lb/A of 2, 2-dichloropropionic acid (dalapon) combined with tillage did not kill more than 95% of quackgrass (Agropyron repens (L.) Beauv.). Best treatment was to rejuvenate the quackgrass in the spring by thorough tillage, apply the dalapon when the resprouts were 4 to 6 in tall, till thoroughly again about 2 weeks later, and then till at monthly intervals until freeze-up. The type of implement used was not important, providing the quackgrass rhizomes were thoroughly shredded. With rates of dalapon at or below 20 lb/A, no residual effect occurred on cereal crops planted in the spring following the year of treatment.

Gas chromatographic and thermoelectric methods were combined in a quantitative study of absorption and movement of 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in bean plants in various intensities of moisture stress.

Foliar absorption of the herbicides studies was unaffected by extreme moisture stress. Herbicidal movement in the plant was markedly reduced, however. Distribution patterns were affected only when stress was permitted to progress to the wilting point. Picloram was more mobile than 2,4,5-T at all stresses.

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.

Sorghum (Sorghum bicolor (L.) Moench) yields were correlated negatively with weed yields and positively with stover yields, sorghum heads per plant, and sorghum weight per 1000 seeds. Sorghum yields were not different when weeds were removed 1, 2, or 3 weeks after planting and each week thereafter, but a significant yield decrease occurred each week when weeds were not removed for 4, 5, 6, or 8 weeks. Sorghum kept weed-free the first 4 weeks after planting showed little yield loss from weeds emerging later. Weeds left after two cultivations reduced sorghum yields 38% below plots weeded weekly. As weed competition increased, sorghum grain yield, stover yield, sorghum heads per plant, seed weight per head, and weight per 1000 seeds decreased, whereas sorghum seed moisture at harvest increased.

Narrow bands of activated charcoal sprayed on the soil surface directly over the rows seeded with alfalfa (Medicago sativa L., var. Cayuga) in the field protected the legume from damage by a broadcast application of 2-isopropylamino-4-(3-methoxypropylamino)-6-methylthio-s-triazine (hereafter referred to as G-36393). Charcoal suspended in water and applied at 25 to 50 lb/A, gave adequate protection from 1.5 lb/A G-36393. Higher rates of charcoal, 100 lb/A, were necessary to protect the legume from a 3.0 lb/A application. Charcoal did not protect alfalfa seedlings from 1.5 lb/A 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine).

Purple nutsedge (Cyperus rotundus L.) was grown under greenhouse conditions as single tubers and various tuber chain systems. Single and repeated applications of amine methylarsonate were made to shoots of single tubers and shoots of terminal tubers in chain arrangements, and visual toxicity symptoms were noted in shoot growth both from treated tubers and from other tubers in chain arrangements. Arsenic (As) was translocated (as indicated by As content) laterally to tubers separated by at least four tubers from the treated shoot. The tuber on the opposite end of the chain from the treated shoot tended to be higher in As content than the middle tubers, and translocated As tended to be higher in tubers from which active growth was present or developed. No apparent relationship was found between As content of tubers and their ability to produce new shoots. There was some tendency for tubers to produce more than one shoot in the initial regrowth following treatment. Tuber lethality following repeated treatments evidently was due to depletion of food reserves and/or bud supply from increased sprouting and not to the accumulation of a specific level of As in the tuber.

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.

A laboratory assay method was developed for studying pricklypear (Opuntia sp.) responses to herbicides. Herbicidal translocation from one pad to another and lateral translocation across a pad appeared to be very slight. Pads were killed when a butoxy ethanol ester, a propylene glycol butyl ether ester, or a 2-ethylhexyl ester formulation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was applied to only one side. Increasing temperatures from 21 to 43 C increased the rate of killing pads. Concentrations of 2,4,5-T at 8 lb aehg of solution usually killed the pad at temperatures above 21 C. Concentrations of 2,4,5-T at 4 lb aehg or less had little effect on the pads. Relative humidity level had little effect on 2,4,5-T activity, but the activity of a propylene glycol butyl ether ester of 2,4-dichlorophenoxyacetic acid (2,4-D) was more effective at the 90 to 95% level than at levels ranging from 30 to 75%. Water, diesel oil, and three diesel oil:water mixtures had little effect on 2,4,5-T toxicity. More toxic effects were shown by 2,4,5-T than 2,4-D. The propylene glycol butyl ether ester, the butoxy ether ester, and the 2-ethylhexyl ester of 2,4,5-T were equally effective on pricklypear at the same concentrations.

In field, soil culture, and nutrient culture experiments, 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) increased percent total nitrogen in all species studied, whether resistant, intermediate, or susceptible to 1 lb/A of atrazine. However, nitrogen content per plant was either unaffected or decreased by these atrazine treatments. One lb/A of atrazine increased percent protein and nitrate nitrogen in most species studied. Atrazine susceptibility apparently was related to its effect on percent non-protein and ammonia in the species tested. One lb/A of atrazine had no effect on percent non-protein nitrogen and decreased percent ammonia nitrogen in resistant species but increased both fractions in intermediate and susceptible species. One lb/A of 2-hydroxy-4-ethylamino-6-isopropylamino-s-triazine (hereafter referred to as hydroxyatrazine), a degradation product of atrazine, had no consistent effect on any nitrogen fraction studied.

The use of preplow foliar application of 2,2-dichloropropionic acid (dalapon) for two seasons, a pre-emergence soil incorporated treatment of ethyl N,N-dipropylthiolcarbamate (EPTC) for three seasons, and tillage during all 3 years was effective in the control of Johnsongrass (Sorghum halepense (L.) Pers.) while corn was being produced on the land. The use of tillage alone, dalapon plus tillage, or EPTC plus tillage resulted in neither satisfactory Johnsongrass control nor corn yield. Dalapon plus tillage reduced the rhizomatous Johnsongrass population and increased corn yield the season following preplow treatments; reinfestation occurred, however, from Johnsongrass seedlings that emerged in the row after the corn was planted. EPTC afforded early season control of seedling Johnsongrass. EPTC plus tillage did not satisfactorily control Johnsongrass or increase corn yield over tillage alone. Injury to corn planted 1 in deep was noted in the first season's treatments; however, corn planted 1½ in deep in subsequent years was not affected.