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.

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.

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.

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 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.

The responses of herbicides applied singly are used in calculating the “expected” response when they are combined. The expected response for a combination is obtained by taking the product of the percent-of-control values for herbicides applied alone and dividing by (100)n-1 where n is the number of herbicides in the combination.

Two morphological types of tubers of yellow nutsedge (Cyperus esculentus L.) were collected over a 2-year period and were sprouted in the laboratory. Tuber dormancy occurred during late summer and early fall. Sprouting was highest during the winter and spring. Mechanical disturbance of the nutsedge stand increased tuber sprouting. Available carbohydrates followed a pattern similar to sprouting; minimum levels were found during late summer. The two types of tubers appeared to be similar in respect to the characteristics studied.

Heights of corn and giant foxtail (Setaria faberii Hermm.) were measured during 1963, 1964, and 1965 in east-central Illinois to establish guidelines for postemergence control of this weed in corn. With an average planting date of May 9, corn grew to a height of 6 in and foxtail 2 in by May 28. With corn growing at a daily rate of 1 in and foxtail ½ in from June 5 to 20, foxtail height was 40 to 45% that of corn.

Two fish from South America. (Metynnis roosevelti Eigenmann and Mylossoma argenteum E. Ahl.), both called silver dollar fish, grazed rapidly on several species of submersed aquatic weeds. Horned pondweed (Zannichellia palustris L.), American pondweed (Potamogeton nodosus Poir.), and sago pondweed (Potamogeton pectinatus L.) were most palatable to the fish. Richardson pondweed (Potamogeton richardsonii (Ar. Benn.) Rydb.), curlyleaf pondweed (Potamogeton crispus L.), and American elodea (Elodea canadensis Michx.) also were grazed. The fish readily grazed on shoots of all sizes except those of mature plants. The Mylossoma grazed the plants more rapidly than the Metynnis. When water temperatures were above 70 F, the fish became more active in their feeding habits.

The quantities of chloroplast proteins and chlorophyll were lower in oat plants treated 6 days with 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) than in the controls. Radioactive amino acid incorporation into chloroplasts indicated that the reduced levels of protein resulted from reduced synthesis. Glucose improved the amino acid incorporation in the treated tissue, but still the rate was reduced markedly by the simazine treatment. An effect of simazine even in darkness on amino acid incorporation into chloroplasts was suggested by the data. Total ribonucleic acid (RNA) content and synthesis as measured by incorporation of p32 were altered by simazine treatments.

Methods of extraction, cleanup, and determination of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) residues from soil were studied. Two-hr soxhlet extraction with methanol was more efficient than shaking extraction with methanol or other solvents. The most successful cleanup method was the use of grade IV basic alumina columns. Polyethylene coated alumina columns were useful if the soil extracts contained high amounts of pigments. A pyridine-alkali-ethylcyanoacetate method of determination was more sensitive and had better color stability than the pyridine-alkali method. Another advantage of the method with ethylcyanoacetate was that a pink chromophore was determined rather than a yellow chromophore which is subject to high interference from yellow pigments from soil extracts.

The control of vegetation along fence lines was studied using 1,2-dihydropyridazine-3,6-dione (MH) at rates of 0, 8, 10, and 12 lb/A. MH reduced plant height, did not change the number of leaves, decreased number of seed stalks, increased the number of discolored leaves, and decreased the uneven appearance. The leaf discoloration was linearly related to the application rates. Observations on species' susceptibility showed a considerable interspecies variability to MH effects. MH at 10 lb/A applied in narrow bands was effective in decreasing maintenance work along fence lines without reducing the protective cover.

Rates of dissipation of 6,7-dihydrodipyrido [1,2-a:2’,1′-c] = pyrazidiinium salt (diquat) and 1,1′dimethyl-4,4′-dipyridinium salt (paraquat) in water were studied from 1963 to 1965 at Davis, California. Effects of several environmental factors on dissipation of the herbicides, and herbicidal control of 9 to 14 aquatic weeds and toxicity to three kinds of fish and an Asiatic clam also were investigated.

Small amounts of the herbicides were still detectable in water at the end of 12 days. In reservoirs, diquat applied at 1000 ppbw or less dissipated to 9 ppbw or less. In growth pools, a concentration of 4000 ppbw dissipated to between 600 and 900 ppbw. Dissipation of paraquat in reservoirs was slower than diquat and exhibited unpredictable fluctuations in amounts present. When 250 to 2500 ppbw of paraquat were applied in reservoirs, 0 to 180 ppbw remained after 13 days. In growth pools, 80 to 300 ppbw of paraquat persisted on the 12th day after applications of 1000 to 3000 ppbw.

Studies conducted near Bernardo, New Mexico, from 1962 to 1964 involved the influence of environment on weekly shoot growth and carbohydrate storage in roots and stems of undisturbed saltcedar (Tamarix pentandra Pall.) and of regrowth (plants regrown from having been mowed the previous winter). Environmental variables were air and soil temperatures, relative humidity, wind, solar radiation, barometric pressure, evaporation from a free-water surface, depth to water table, and water quality. No variable or combination of variables could be used to predict accurately the maximum shoot growth period or the minimum carbohydrate storage. An analysis of the individual weekly growth patterns of plants showed considerable week-to-week variation in the rate of growth. Wide variations in total carbohydrate storage in roots and stems within weeks also were evident, and probably reflected the variation in growth.

Methods of weed control and seeding of perennial grasses on rangelands infested with downy brome (Bromus tectorum L.) in Nevada and northeastern California were compared for 4 years. In this study, 1, 1′-dimethyl-4,4′-bipyridinium salt (paraquat) at 0.5 lb/A and higher gave adequate and consistent control of downy brome for establishment of perennial grasses. Disking gave weed control and perennial grass establishment generally comparable to that of paraquat. Weed control from furrowing alone usually was not adequate for establishment of good stands. Seeding in furrows combined with paraquat spraying or disking gave best seedling establishment. Establishment of intermediate or pubescent wheatgrass (Agropyron intermedium (Host) Beauv. and A. trichophorum (Link) Richt.) was better than crested wheatgrass (A. desertorum (Fisch.) Schult.). Precipitation in different years, site potential, and weed population at different locations influenced weed control and establishment of perennial grasses.

Histological abnormalities were found in Canada thistle (Cirsium arvense (L.) Scop.) roots after plants received foliar treatments of 4-amino-3,5,6-trichloropicolinic acid (picloram). These abnormalities included destruction and distortion of cortical cells and cambial and phloem disintegration. Some or all of these conditions were present, depending upon which portion of the root was sectioned.

In an attempt to improve the metering of herbicides applied to soil in horticultural plantings, loosely knitted cellulose acetate cloth was impregnated with herbicides, using appropriate acre rates as determined by those used in spray applications. Treated cloth was placed on the soil and the edges anchored or the cloth was lightly covered with soil. Adjacent plots were sprayed with the same herbicides. The herbicide-impregnated cloth was as effective as spray applications of 12 of the 15 herbicides used.

Foliar and soil herbicidal treatments were made on creosotebush (Larrea tridentata (DC.) Cov.), tarbush Flourensia cernua DC.), and whitethorn (Acacia constricta Benth.) near Tombstone, Arizona, from 1957 to 1964. All herbicides were most effective when applied approximately 30 days after initiation of the summer rainy season. The herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were about equal in effectiveness, but the relative susceptibility of the individual shrubs to the herbicides varied with treatment conditions. The acetic form of 2,4,5-T generally was more effective than the propionic; propylene glycol butyl ether, iso-octyl, and tetrahydrofurfuryl esters more effective than pentyl. Foliar applications of 4-amino-3,5,6-trichloropicolinic acid (picloram) were most effective on whitethorn, intermediate on creosotebush, and least effective on tarbush. The most effective soil herbicidal treatments were 3-phenyl-1,1-dimethylurea (fenuron) and 3-(p-chlorophenyl)-1,1-dimethylurea (monuron). In general, effective control of dominant Chihuahuan Desert shrubs required 2 to 4 lb/A of 2,4-D or 2,4,5-T, 14 to 1 lb/A of picloram, or 2 lb/A of fenuron or monuron.

Measurements were made of plant toxicity and of several physical and chemical properties of spray solutions containing 1,1′-dimethyl-4, 4′-bipyridinium salt (paraquat) and either anionic, nonionic, or cationic surfactants. Surface tension and pH values were variable among 10 surfactant-paraquat mixtures and also at 0.1 and 1.0% surfactant concentrations, but neither showed any correlation with herbicidal activity on corn when all surfactants were considered. All four nonionic, both cationic, and two out of four anionic surfactants markedly enhanced paraquat toxicity at appropriate concentrations. Studies of UV absorbance of herbicide and surfactant solutions, alone and in combination, and adsorption of paraquat-C14 at solution-air interfaces indicate that significant interactions occurred between paraquat and the anionic surfactants. Foliar toxicity studies offered substantiating evidence of such interactions; however, the degree or lack of enhancement of paraquat toxicity was strongly influenced by plant species (corn vs. bean) and the type and concentration of surfactant. No surfactant-paraquat combinations studied were less effective than ⅛ oz/A of paraquat used alone.

Three facets of the phytotoxicity of disodium methanearsonate (DSMA) incorporated in soils were studied in seven greenhouse experiments. Growth of cotton planted immediately after incorporation of DSMA in Bosket silt loam was reduced significantly by herbicide concentrations of 50 to 80 ppmw. Toxicity appeared to decrease with time, particularly during the first 16 weeks after incorporation. DSMA incorporated in Bosket silt loam at 120 ppmw did not inhibit significantly the growth of cotton planted 32 weeks later. The addition of phosphorus to two silt loam soils increased the toxicity of DSMA to cotton. The incorporation of 50 ppmw of DSMA in Bosket silt loam inhibited rice growth by 75%, soybeans by 39%, oats by 12%, corn and cotton by 10%, and wheat by 0%. Rice growth was not affected in Dubbs silt loam or Sharkey clay by DSMA at concentrations as high as 100 ppmw.