The control of hardwood vegetation is an essential step in establishing pine on upland sites in North Louisiana. In some instances removal of all vegetation is necessary before pine seeding or planting can be done. This type of operation is usually accomplished by conventional land-clearing methods, which are often rather expensive. The use of chemicals as a means of hardwood control offers certain advantages not inherent in mechanical methods. In situations where species selectivity is not desired, the substituted urea herbicides might provide an economical means of vegetation control.

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).

The need for information concerning effects of quality and quantity of light on submerged aquatic plants has been emphasized by the Committee on Aquatic Weed Control at the Southern Weed Conference and by Westman. Factors such as light intensity, water temperature, and depth of water interact with soil fertility to govern the establishment of rooted aquatic vegetation and determine the rate at which it grows.

A number of s–triazine derivatives have shown considerable promise for pre-emergence weed control. Activity and selectivity as influenced by structural differences between many derivatives have been discussed by Gysin. The phytotoxicity of some of these materials is greatly influenced by the characteristics of the soil to which the herbicides is applied. Although solubility may be important in the toxicities of the s-triazines, adsorption may be of equal or greater importance in the presence of high organic matter or high colloid content. In solution these factors may be eliminated so that a more accurate determination of phytotoxicity and physiological selectivity may be made. The most successful pre-emergence herbicides for shallow planted crops possess at least some physiological selectivity.

Canada thistle and perennial sowthistle have been given several names by various authors. However, it appears that the Canada thistle used in this study is generally called Cirsium arvense (L.) Scop. and the perennial sowthistle was a mixture of Sonchus arvensis L. and S. uliginosus Bieb. The two species of sowthistle are very similar. However, S. arvensis has “long glandular-hispid peduncles and involucres covered with lead colored glandular phyllaries” and a chromosome complement of 54, while S. uliginosus has “slenderly turbinate to cylindric pale involucres and glaborous white-margined phyllaries” and a chromosome complement of 36.

Drift of spray droplets is a major problem in the application of insecticides and herbicides. Spray drift is the movement of the spray from the place of application to adjacent areas by wind or air currents. Many insecticides and herbicides are effective in minute quantities and even the small amount that drifts can be harmful to crops and livestock. Parathion, 2,4–D, and 2,4,5–T are among those chemicals whose drift is a problem where they are used.

One of the major prerequisites to a study of the vegetative buds on the rhizomes of quackgrass is the development of a method in which the rhizomes may be grown where bud growth can be observed easily. Since buds on the rhizomes of quackgrass are subterranean and since immediate observations of growth responses are virtually impossible, it was concluded that a method should be devised which would provide in vitro conditions favorable for growth. Changes in bud activity or dormancy could then be followed throughout the growing season. The method should also be such that observations of and treatments to the rhizomes could be made without disturbing them. Several methods have been used previously, but they do not lend themselves readily to observation or treatment.

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.

The sodium salt of 2,2–dichloropropionic acid (dalapon) has found a place in chemical weed control practices because of its effectiveness against grasses. The nature of its action is understood only poorly.

Wild oats (Avena fatua L.), winter rye (Secale cereale L.), and volunteer winter wheat (Triticum vulgare Vill) are troublesome problems to many areas in the West. Wild oats are one of the most troublesome weeds on irrigated lands. Winter rye is a problem on dry lands planted to winter wheat. Volunteer wheat on dry lands makes it almost impossible to keep varieties pure, and consequently it is difficult to produce certified seed under these conditions. Volunteer susceptible varieties become infected with bunt and this not only causes the wheat to grade smutty, but also perpetuates the bunt organism so it can hybridize and produce new races.

The materials known as herbicides represent many different chemical groups. Well-known herbicides include aromatic hydrocarbons, halo-aryloxy organic acids, substituted carbamates, substituted ureas, sulfamates, cyanates, substituted phenols, symmetrical triazines, and many others.

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 use of herbicides in row crops in areas where furrow irrigation is used presents unique conditions for the use of soil applied herbicides. Pre-emergence herbicides have not been as uniformly successful under arid irrigated conditions as they have been in areas of frequent rainfall. Soil incorporation of many herbicides in the top few inches of soil has resulted in improved performance under furrow irrigation.

Improved methods of weed control through use of herbicides offer important means of reducing production costs and labor requirements in irrigated cotton. The use of pre-emergence herbicides has proved to be an effective tool for annual-weed control in cotton in the humid southeastern cotton region of the United States. Research in Arizona has shown that certain herbicides applied at layby (immediately after the last cultivation) are effective for the control of late-season annual weeds in cotton.

Treatment of soil with fumigants to kill dormant weed seeds is a valuable practice but control in the surface one or two inches is often poor. This is because the fumigant vapors diffuse rapidly out of the soil into the atmosphere before building up a lethal concentration near the surface. Improved weed control has been reported by proper confinement of fumigant vapors in the soil with impervious seals. Water seals have been advocated by some workers as a satisfactory substitute for impervious covers. However, only limited experimental data are available comparing soil fumigation results with different methods of sealing the soil surface.

N–(3,4–dichlorophenyl)methacrylamide (hereafter referred to in this paper as DCMA) is a relatively new compound in the field of herbicides. However, several weed control workers (personal communication) have suggested that DCMA may be of value for control of crabgrass (Digitaria spp.), brachiaria (Brachiaria spp.), pigweed (Amaranthus spp.), morning glory (Ipomoea spp.), cocklebur (Xanthium spp.), and goosegrass (Eleusine indica), common weeds found in cotton.

Considerable attention has been given during recent years to the fate of herbicides sprayed onto soil surfaces. The effect of light upon herbicides also has been studied extensively. Payne and Fults by means of a biological test found that the potency of 2,4–D was increased by exposure to ultraviolet light. Hansen and Buchholtz found that when a solution containing 2,4–D and riboflavin was exposed to light the activity of 2,4–D was reduced. They tentatively identified the breakdown product as 2,4–dichlorophenol. Later Bell positively identified it.

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.

Dalmatian toadflax (Linaria dalmatica (L.) Mill.), a native of southeast Europe, has acquired a firm position in some plant communities in northeastern Washington. The first herbarium specimen for Washington State University was collected in 1926 on the Little Spokane River near the city of Spokane. Since that time, it has invaded a considerable area of northeastern Washington, and scattered patches appear over much of the eastern half of the State. In 1954 the estimated acreage was 30,000. Dalmatian toadflax has now spread into Idaho, western Montana, and Oregon. It also occurs in the prairie provinces and inter-mountain regions of Canada and has been reported near Flagstaff, Arizona.