Cluster tarweed (Madia glomerata Hook.) is an annual which occupies rangeland from Saskatchewan to N. Arizona at medium to high elevations. In the laboratory dried tarweed plants and leachates from them reduced the germination of intermediate wheatgrass (Agropyron intermedium (Host) Beauv.) and radish, and caused high proportions of abnormal seedlings. The inhibitory agent(s) was highly water soluble, dialyzable, stable to boiling, drying, and prolonged storage in solution, destroyed by ashing, and not affected by pH 4 to 7. In soil in the greenhouse, tarweed leachates and dried tarweed significantly reduced growth of wheatgrass seedlings. In the field, tarweed infestation reduced the establishment and growth of wheatgrass sown in it in proportion to the stand of tarweed.

Yellow rocket (Barbarea vulgaris R. Br.) was studied for 5 years under field conditions. Yellow rocket seeds germinated throughout the growing season, but vernalization of the rosettes formed was necessary for flowering. There appeared to be a minimum size plant that could be vernalized. In the spring vernalized rosettes formed flower stalks. As the flower stalk elongated, basal rosette leaves died, giving the impression of an annual. When the flower stalk was cut or seed matured, new rosette leaves developed from buds on the crown. This new growth was capable of going through the subsequent winter. Marked plants survived for at least 3 years. The ability to flower again and set viable seed in the same year after cutting appeared to be associated with the stage of the original flower stalk when cut. Yellow rocket is perennial, but it may not survive after its second year under conditions of disease or strong competition.

Spot-treatments of young cotton with 2,2–dichloropropionic acid, simulating control of clumps of perennial grass, resulting in 10 to 25% reductions in cotton stands, did not cause proportional reductions in yields of seed cotton. Increased growth of cotton plants adjacent to skips compensated for reduced stands. The treatments did not affect boll components or fiber properties of cotton.

Patterns of absorption and distribution of dalapon (2,2–dichloropropionic acid) were determined by radioautography and counting. Dalapon was absorbed through the cuticle and through the large open pores of hypostomatous leaves. Stomata were clearly the most expeditious routes of entry, but results were erratic when no surfactant was included. An anionic surfactant, sodium dioctylsulfosuccinate, enhanced both (a) cuticular and (b) stomatal plus cuticular penetration 3- to 4-fold during a 2-hr. absorption period. Studies confirmed the view that dalapon is translocated to regions of high metabolic activity and/or storage in association with and dependent upon the movement of food materials. Dalapon did not move appreciably out of albino leaves or green leaves previously depleted of food reserves, but was transported readily out of normal leaves in the light when a surfactant was used to enhance cuticular penetration.

A significant amount of amiben (3–amino–2,4–dichlorobenzoic acid) was leached from the 0 to 1-inch soil depth with 1 and 2 inches of applied water. Weed control could be obtained from amiben at 1 lb/A if rain came within 3 or 4 days after application. One-half inch of water applied immediately after application markedly increased the toxicity of 1 lb of amiben per acre to Brassica juncea (L.) Coss and Panicum miliaceum L.; a similar response from 2 lb/A was obtained with 1/4 inch of water. As the amiben rate was increased, less water was required for optimum weed control. Increased water and/or amiben applications were required with Brassica campestris L., which is somewhat resistant to amiben.

Nutsedge tubers germinated readily in soil treated with EPTC. However, growth was suppressed and emergence delayed, the delay depending on the rate of application. EPTC at 12 and 16 pounds per acre with 8 and 12 weeks exposure was very effective in killing nutsedge tubers as indicated by tuber germination and condition of tubers that did not germinate.

The granular formulation of EPTC killed highly significantly more nutsedge tubers than the emulsifiable formulation. Repeat applications of EPTC were significantly better in terms of tubers killed than single applications of the same rate of the herbicide. Thorough incorporation of EPTC to a depth of 5 inches of mechanical means was significantly more effective than incorporation by leaching.

Applications of 2,4–dichlorophenoxyethyl sulfate (sesone) were made to obtain a wide range of formative response in peanut seedlings. These reactions were rated (0 = no effect, 10 = complete kill) as the peanut seedlings emerged, and correlated with growth and development of the plants. It appears that plants from seedlings in the 0 to 3 range of response have an excellent chance to develop into healthy, productive plants. The seedlings in the 3 to 5 range have a questionable chance. The seedlings in the 6 to 10 range have little chance, because root rots were both frequent and severe at 8 to 9 weeks after seeding.

In the Peace River region, vegetative shoots of field horsetail, Equisetum arvense L., emerge from June 1 to July 1, and reach full growth about July 16. All herbicides studied were most effective applied July 16 to 30. Amitrole (3–amino–1,2,4–triazole) at 8 lb/A at this time gave 96% stand reduction the next year. For selective killing in barley, MCPA (2–methyl–4–chlorophenoxyacetic acid) at 4 to 8 oz/A killed 100% of the top growth in the year of application and gave 50 to 65% stand reduction the next year. Other herbicides tried were less effective.

All herbicides were incorporated either as pretransplanting or posttransplanting treatments. Herbicides used were: ethyl N,N–di–n–propylthiolcarbamate (EPTC), propyl N,N–di–n–propylthiolcarbamate (1607), ethyl N,N–ethyl–n–butylthiolcarbamate (2060), propyl N,N–ethyl–n–butylthiolcarbamate (2061), O–(2,4–dichlorophenyl) O–methyl isopropylphosphoramidothioate (DMPA), 2–chloro–4–diethylamino–6–ethylamino–s–triazine (trietazine), and the dimethyl ester of 2,3,5,6–tetrachloroterephthalic acid (DCPA). EPTC, 1607, 2060, and 2061 at 3 lb/A (repeated 3 times), posttransplanting, and DMPA at 20 lb/A, pretransplanting, gave control of the annual weeds present with the exception of annual morningglory, and had no effects on tobacco yield or value. Nicotine, nornicotine, total alkaloids, and reducing sugar content of the cured leaf were not adversely affected by the thiolcarbamates, DMPA, amiben, or DCPA at rates used. Smoke and taste tests of tobacco treated with EPTC, DMPA, amiben, and DCPA revealed no undesirable flavors.

Weed control has been a major problem in Hawaiian pineapple production. Hand-hoeing and mechanical cultivation gave way to activated oil emulsion sprays in the 1940's. The 1950's brought the use of preemergence herbicides especially 3–(p–chlorophenyl)–1,1–dimethylurea (monuron). Each method has brought a shift in species distribution. Today, large-seeded species and vegetatively-propagated species are less well-controlled than in the days of contact weeding with oil emulsion sprays. There is need for selective herbicides which will control the weeds which escape the present program.

Winter wheat infested with four populations of coast fiddleneck (Amsinckia intermedia Fisch. & May) was treated with 2,4–dichlorophenoxyacetic acid (2,4–D). One weed per square foot reduced grain yield. Weeds competed strongly as early as the rosette stage. Treating the weed infested wheat with 2,4–D increased yield. A vigorous, early-established crop of wheat competed effectively with the weeds.

During a 48 hour period after spraying with 2,4–dichlorophenoxyacetic acid (2,4–D), the ribonucleic acid (RNA) in the subcellular particles of soybean hypocotyl tissue doubled with over half of the increase appearing in the microsomal fraction and one quarter in the soluble fraction. It is hoypothesized that the herbicidal action of 2,4–D lies in a renewal of nuclear activity in the tissue, leading to a synthesis of RNA and protein and to tissue proliferation, and that the cytochemical basis of auxin-herbicide action lies in a reversion to a meristematic metabolism.

Medusahead (Elymus caput-medusae L.) matures later in the spring than most associated species, and has a seed head moisture content of above 30 per cent for approximately a month after leaves and stems begin to dry. High temperature is more injurious to seed viability when seed moisture content is high. Control burns of medusahead infested rangeland were most effective in late afternoon when burning slowly (into a mild wind) and at the soft dough stage of medusahead seed development.

A procedure has been described for the partial purification of the simazine-resistance factor of Zea. The relative solubilities in various solvents and some of the chemical properties of this factor have been studied. Pyridine and hydroxylamine were also found to bring about the conversion of simazine-C14 to the 2–hydroxy analogue. Based on these substances as models, a mechanism has been proposed for the dechlorination of simazine in Zea.

Seedlings of barnyardgrass, green foxtail, and yellow foxtail emerged from seeds as deep as 5 inches in Sagemoor fine sandy loam. The number of emerged seedlings from depths of 4 to 5 inches decreased in the order of decreasing seed weights; yellow foxtail, barnyardgrass, green foxtail. Few seedlings developed in the field from seeds on the soil surface. Seedling emergence in spring or greenhouse seedings was greatest from the most shallow depths (½ or 1 inch) and decreased regularly as depth of planting increased. An autumn seeding gave maximum emergence at 1½ inches, possibly because some seeds sown shallower may have germinated in short warm periods but were killed by subsequent freezing.

Comparative studies of herbicides and herbicide mixtures were conducted at Tifton, Georgia, in 1959 and 1960. Certain mixtures, which contained sodium 2,4–dichlorophenoxyethyl sulfate (sesone), tris(2,4–dichlorophenoxyethyl) phosphite (2,4–DEP), or the triethylamine salt of 3–amino–2,5–dichlorobenzoic acid (amiben) mixed with the alkanolamine salt of 4,6–dinitro–o–sec-butylphenol (DNBP), gave seasonal weed control on band-treated peanuts. Compared to herbicides applied singly, mixtures not only increased the spectrum of weeds controlled but also permitted the use of the lowest rate of each component on the weeds for which it was most effective.