In field practice much of the application of herbicides to local infestations of bermudagrass (Cynodon dactylon L.) is done by hand on a spray-to-wet basis. With a fixed concentration of active ingredient in the spray mixture the dosage is determined by the volume used in wetting a particular stand of grass. The amount of herbicide deposited on the weed foliage may be affected by the addition of surfactants to the spray mixture. In orchards and vineyards where the tolerance of the crop to the herbicide is limited, variations in the stand may lead to local overdosage and injury to the trees and vines.

Recent reviews [Crafts, Currier, Woodford] dealing with the mode of action of phytotoxic chemicals claim the acute toxicity of petroleum oils to plant tissues is due to the destruction of the plasma membrane of the cell. Although considerable evidence supports such a claim, much of it rests on results from the effect of vapors on greenhouse grown plants rather than on the effect of liquid oils on field grown plants. Of the numerous workers who have noted a selective action of oils on different plant species, most of them determined the selectivity by visual observation of injury. Currier and Peoples, Dallyn, and Van Overbeck and Blondeau linked the selective action by experimentation to a differential effect on a cellular level but only the work of Currier and Peoples included direct determinations of cellular vitality. It seemed desirable, therefore, to obtain further information on the relative susceptibility to petroleum oils of field-grown plants.

The general acceptance of cytochrome oxidase as the terminal link between the various dehydrogenase systems and oxygen in plants was stated in the reviews by Smith and Chance, James, and Hartree.

Madrone (Arbutus menziesii Purch.) and tanoak (Lithocarpus densiflora (H & A) Rehd.) are often considered undesirable along the Pacific Coast. These weed trees are removed to increase forage production; to remove competitors of more valuable timber trees, especially Douglas fir (Pseudotsuga menziesii (Mirb) Franco); or to obtain firewood or charcoal. Tanoak is occasionally cut for tanbark harvest. Control of stump sprouting following cutting would be desirable.

The herbicide EPTC (ethyl N,N–di–n–propylthiolcarbamate) offers much promise as a soil-borne toxicant for controlling a variety of common weeds. Not only does it control annuals; it is proving very effective and quite specific in the control of nutsedge. In this role it is unique among the newer materials. In California it has held nutsedge in check during the whole growing season in strawberries, peppers, beans, and other row crops.

Formulation and preparation of herbicidal chemicals for the selective control of weeds in mechanized crop production have become increasingly more difficult with the introduction of a wide variety of organic and inorganic herbicides during recent years. Commercial herbicides and experimental chemicals are usually applied in systems which contain not only the active ingredients but also various solvents, cosolvents, surfactants (surface-active agents), carriers, and other adjuvants. Formulations of herbicides are usually evaluated for their maximum effects on weeds and minimum effects on crop plants. The manner in which the inactive constituents of formulations influence the ultimate herbicidal activity of the active ingredients is not well understood and extensive research will be required to obtain the fundamental information needed.

Annual grasses continue to be a problem. Some of the most prevalent annual grass weeds are members of the foxtail (Setaria) genus. Although these species can be controlled chemically, farmers have often had failures. One possible cause of these failures could be variability within the species.

Witchweed [Striga asiatica (L.) Kuntze] is an annual parasite which was discovered in North Carolina and South Carolina of the southern United States in 1956. This weed presents a hazard to the economic production of corn, sorghum, sugarcane, and other host plants.

In coastal Oregon, mild climate, highly productive soil, and annual precipitation of as much as 130 inches combine to produce an exceptionally high rate of forest growth. When these forest stands are harvested, however, brush establishes rapidly in the openings, competes strongly with conifer reproduction, and eventually causes a reduction in timber yields. Such losses are serious in a region which depends largely on the timber resource.

The growth promoting activity of substituted benzoic acids and 2,4-dichlorophenoxyacetic acid (2,4–D) was reported in 1942 by Zimmerman and Hitchcock. Interest in benzoic acids as herbicides was revived in 1950 when Bentley reported outstanding growth regulation with 2,3,6–trichlorobenzoic acid. Shortly thereafter several workers confirmed these results. Chlorinated benzoic acids have proven to be effective for eradication of field bindweed, and many other perennial weeds. At the present time these herbicides are labeled and sold for the eradication of field bindweed, leafy spurge, bur ragweed, Canada thistle, and Russian knapweed.

Dodder lowers the yield and quality of alfalfa seed, interferes with harvesting, and adds to the cost of cleaning and processing the seed for market. There are at least three species of dodder that are troublesome in alfalfa seed fields in Utah: Large seeded alfalfa dodder (Cuscuta indecora Choisy var. neuropetala (Engelm.) Hitch.), Western field dodder (Cuscuta campestris Yuncker) and small-seeded alfalfa dodder (Cuscuta approximata Bab. var. urceolata (Kuntze) Yuncker) (Figure 1).

It was discovered in 1952 that 3–amino–1,2,4–triazole (amitrole) possesses defoliating and regrowth inhibiting properties in cotton. Subsequent study has shown that its most dramatic effect is in the inhibition of chlorophyll formation. Since it is readily absorbed by roots, is translocated throughout the plant, is a general growth inhibitor, and is effective in low concentrations, it is a potentially valuable systemic herbicide. It has been used successfully in the control of quackgrass, nutsedge, Canada thistle, and such woody plants as poison ivy.

Citrus and avocado trees have occasionally been injured following use of 3–amino–1,2,4–triazole (amitrole) at rates of 12 or more lb/A for control of perennial weeds. The distribution of tree injury relative to sprayed areas as well as the known low volatility of amitrole has indicated that tree injury was not due to volatility. The initial occurrence of symptoms on sucker growth in the interior and on the top foliage rather than lower exterior foliage of the trees would seem to eliminate spray drift as a possible cause. This injury has appeared to be due to spray residues being leached into the soil and taken up by the roots of the trees.

Water stargrass (Heteranthera dubia (Jacq.) Mac. M.) is a perennial, rooted, aquatic plant indigenous in the shallow lakes, ponds, and slow rivers of the eastern United States. It thrives in the drainage canals of northeastern Arkansas. This area is basically a reclaimed swamp with intermingled soils ranging from pure sand to heavy clay, and the water table is very close to the surface. Water stargrass reduces the carrying capacity of the drainage ditches, resulting in a rise in the soil water table and in flooded or waterlogged soils. Water stargrass makes its greatest growth in the spring during the season of heaviest load on the drainage canals.

The practical use of ethyl N,N–di–n–propylthiolcarbamate [EPTC] has been studied intensively by weed research workers since introduction of the herbicide in 1957. Early studies were devoted to its evaluation as a soil-surface application for control of germinating weed seed. Studies conducted in 1958 showed that the activity of EPTC could be greatly increased by soil-incorporation immediately after application and emphasis shifted to soil-incorporation research. In general, the accumulated applied research data on the use of EPTC in pre-planting, or lay-by, soil-incorporated treatments have emphasized the pressing need for basic investigations on the effects of soil composition and reaction, temperature, light, moisture, method and depth of incorporation, and method of formulation on the activity of this herbicide. A limited number of basic studies have been conducted on the effects of soil composition and moisture on the performance and persistence of EPTC. However, basic research must be intensified if the excellent herbicidal potentialities of EPTC and other soil-active carbamates are to be utilized to their fullest extent.

Simazine, 2-chloro-4, 6-bis (ethylamino)-s-triazine, can give excellent control of annual weeds in corn for most of the growing season. However, a number of workers have reported injury to susceptible crops the year following applications of four or five pounds of simazine per acre. The persistence of simazine is thus of considerable importance to the user who practices crop rotation. The purpose of this study was to investigate factors involved in the dissipation of simazine from the soil.

Absinth wormwood (Artemisia absinthium L.), a perennial, native to Europe, has become abundant during the last decade in several locations in western Canada. Reports received during the Saskatchewan Weed Survey suggest that at least some of the introductions into this area were by immigrants from Europe, who believe it to have medicinal properties. Silver-grey in color and covered with fine hairs, the herbaceous stem grows to a height of 2 to 4 ft, often branching profusely. The leaves are up to 5 in. long and are two to three times divided into lanceolate segments. Numerous, drooping heads, about 3/16 in. in diameter, develop in leafy panicles. Yellow or purple florets are borne on a hairy base. The whole plant has a strong, penetrating odor, common in other species of this genus. In Europe it is used as a stimulant (tea and liquor).

A portable, multiple-tanked spray apparatus has proved convenient and effective for field tests, particularly in steep and remote areas where more elaborate sprayers cannot operate. No hand pumping is necessary and the quickly interchangeable multiple tanks permit mixing and preloading of spray materials in the laboratory. The resultant saving of time in the field often means the difference between completion of a spraying experiment in 1 day rather than 2 or 3, a factor that increases in importance with the remoteness of the research area.

In a recent herbicide development program for control of wild oats (Avena fatua), methods of breaking the dormancy of wild oat seed were studied, since it is difficult to obtain seed with a high rate of germination. One of the theories advanced to explain seed dormancy is that the seed coat acts as a barrier to oxygen penetration. If the seed coat prevents oxygen penetration, then it should be possible to break dormancy by placing seed under high gaseous pressure to force gas through the seed coat, and then rupture the seed coat with a rapid release of pressure.

In the course of an investigation at Madison, Wisconsin, designed primarily to evaluate an improved pea drill, useful quantitative data were obtained relating to weed growth in three different pea populations, verifying the general observation that heavy rates of seeding help to control weeds.