Several investigators have now reported that phenylurea herbicides inhibit the photochemical activity (Hill reaction) of isolated chloroplasts. Many of the phytotoxic symptoms in plants treated with phenylurea herbicides can be explained on the basis that the herbicides have blocked the photosynthetic mechanism. This action has been suggested as the primary cause of toxicity under field conditions. The metabolic product of biochemical pathways containing the primary site of action of a herbicide can be applied to barley plants in sufficient quantity to eliminate completely some of the toxic symptoms produced by the herbicide. Geoghegan has reported that glucose applications caused an increase in the concentration required for three phenylurea compounds to inhibit growth of Chlorella vulgaris. Therefore, a determination of the effect of carbohydrates on the inhibition of growth of barley seedlings in the presence of several phenylurea herbicides seemed of interest.

Pensacola bahiagrass (Paspalum notatum F.) is a leading pasture grass in the Southeastern and Gulf Coast states where it produces high quality forage on relatively infertile soils low in available moisture. It is a major seed crop on which many farmers rely as a cash crop. Weeds compete strongly with this grass during its establishment and even after establishment of a sod, various annual or perennial weed species may encroach. Control of such weeds often is desirable.

Barnyardgrass (Echinochloa crusgalli (L.) Beauv.) is the most serious weed in rice in Arkansas and this and other species of Echinochloa are a serious problem throughout the rice-growing areas of the world. A limited field survey conducted in August 1957 in the Grand Prairie rice-growing region of Arkansas indicated that 27 percent of the rice fields were infested with barnyardgrass. Presumably the yield of rice on these fields could have been increased substantially by controlling the barnyardgrass.

The literature does not reveal any direct information concerning the time of exposure or concentration required of a soil fumigant to kill weed seeds. For specific soils and conditions the appropriate rate of application may be known but this does not represent an actual toxic concentration. This is due to the fact that the toxicity of the fumigant may be decreased due to adsorption of the fumigant by the soil or solution in the soil water. This investigation was carried out to determine what concentration of fumigant is needed for a specific time to produce a given percent control of dormant imbibed seeds.

The possibility of using 2,4-D as a soil sterilant was investigated by Crafts in 1949. He concluded that 2,4-D may be useful under very dry conditions. In 1954, Shafer reported several years work using soil applications of 2,4-D for control of perennial weeds. Since that time many research workers have evaluated 2,4-D and other phenoxy herbicides for the control of bindweed and other perennial weeds. Results of these trials varied from excellent to poor.

Although Russian knapweed is not as widespread as some of the other deep-rooted perennial weeds, thousands of acres of farmland are infested and it is spreading. It is generally called Centaurea repens L., according to Fernald and Stevens, though it also is referred to as C. picris Pall. Stevens states that there is some question about the identity of C. repens.

The remarkable spread of a seed-bearing Spartina species (formerly incorrectly known as S. townsendii H. & J. Groves, now awaiting a new name) in mudflat areas on European coasts in the past 70 years is widely known. It was suspected from the sudden appearance of a new Spartina species in Southampton Water during the latter part of the 19th Century amongst accidentally introduced Spartina alterniflora Lois, and the British native Spartina maritima (Curt.) Fernald, that the plant was of hybrid origin. Some of the plants were found to be polyploid and this suggested an explanation for the extreme vigour and fertility of those plants which rapidly spread from Southampton Water, east and west along the south coast of England.

In 1950 an experiment was initiated at Mississippi State University to evaluate the comparative efficiency of certain promising herbicides in controlling weeds in cotton. The use of herbicides for weed control in cotton was beginning to be accepted as an agricultural practice. Results from a long-time experiment involving the use of herbicides for weed control in cotton were needed.

The recognition of the herbicidal activity in the phenylacetic acids by Pybus et al. is a matter of particular interest to those whose work is concerned with weed control in crops unusually sensitive to 2,4-D (2,4-dichlorophenoxyacetic acid) and its derivatives.

In using non-fortified oils for post-emergence weed control in cotton, it has been necessary to follow certain precautions because of differential plant response at different stages of cotton growth. Several workers emphasize that certain oils can be applied safely to young cotton hypocotyls three weeks after emergence, but as soon as small bark cracks begin to appear at the base of the stem, oil usually causes injury. Palmer and Ennis found that when an oil was applied to cotton stems 14 to 80 days old, it injured the stem, and reduced final yields when cotton was 27 to 59 days old at time of application. Plants less than 27 days old and more than 59 to 80 days old were not injured by the oil.

In order to protect young apple trees, in the years immediately following planting, from competition for moisture and plant food it is a generally accepted practice to keep the area around the trees free of weeds. The traditional method of doing this has been to clean cultivate, the area next to the trees being kept clean by hand labour.

Blue oak (Quercus douglasii) is a common tree on several million acres of grazing land in California. It may occur as pure stands, but other species of woody plants, especially poison oak (Rhus diversiloba), are commonly associated with it. Leonard and Harvey, et al. reported the effectiveness of the cut-surface method using 2,4–D amine for killing blue oak. Unfortunately, killing of the blue oak results in a “release” of some of the under-story shrubs, which may become a problem later. A broadcast spray that will control all the woody plants is needed.

Quackgrass, Agropyron repens, is the major weed problem on at least half of the acreage planted to potatoes in Michigan. The northern counties of the lower peninsula and much of the upper peninsula have an ideal climate for quackgrass, and potato growers must include control measures in their production plans. The work reported in this paper was directed toward development of an effective and economical control program.

The concept of reducing tillage operations with herbicides was first tested in California orchards in 1944. In 1949, Johnston and Sullivan gave a detailed discussion of chemicals and equipment needed for eliminating tillage in orchards. Over a 4-year period chemical weed control proved cheaper than cultural methods. Soil condition and water penetration were improved and soil erosion was reduced by chemical weed control.

Bedstraw (Galium mollugo L.) is a deep-rooted perennial weed present throughout New York and many areas of the northeastern United States and Europe. It occurs in pasture, meadows, waste areas and along ditch banks and roadsides. This weed assumed importance comparatively recently and almost concurrently with the increasing popularity and widespread use of birdsfoot trefoil (Lotus corniculatus L.).

The technique used in the tests herein reported is based on the inhibition of root elongation by growth substances, an exceedingly sensitive response. Two procedures are used in the application of the growth substances. The first consists of applying known amounts of test compounds to the root bathing solution of mesquite seedlings, and the second procedure consists of applying these compounds to the cotyledons. After addition of the growth regulator to the solution subsequent root inhibition is dependent on absorption by the root tissue and accumulation in an active form at the site of action. In cotyledonary applications, translocation as well as absorption is necessary before inhibition of root elongation will occur. It was the objective of this study to investigate various possibilities for using these procedures in herbicide absorption and translocation experiments.

This paper reports on the synthesis and properties of 38 new herbicides, amino acid derivatives of 4–(2,4–dichlorophenoxy)– and 4–(2–methyl–4–chlorophenoxy)butyric acids. The biological evaluation of the compounds as selective herbicides is being conducted by other investigators and will be published later.

The first step in a satisfactory forage-legume program on the farm is the establishment of the legume. Success or failure here can mean the difference between a continued efficient rotation system and a financial loss. Many farmers have been reluctant to plow up old seedings at the proper time because of the cost of new seedings and the possibilities of seeding failures. Also, new seedings may appear successful in the seeding year only to be lost during the first winter. This paper is a report of 3 years' study at Ithaca, New York, on the use of herbicides applied pre-emergence to aid in the establishment of forage legumes without a companion grain crop.

Esters of the chlorophenoxyacetic acids are generally considered to be more phy to toxic than the acid or acid salts. Hence the esters have found wide use in herbicidal formulations. Much research has been done on the mode of action of plant growth regulators, but the fate of neutral derivatives of active acids has received little attention, even though an acid side chain is one of the molecular requirements for growth substance activity.

Foxtail barley (Hordeum jubatum L.) is a native, short-lived perennial bunch grass with a wide distribution in the United States. Hay containing the mature spikes can cause severe injury or death to animals fed upon it because of the barbed awns, which work their way into the face and mouth, opening the way for infections.