The search for means of controlling submersed aquatic weeds has emphasized the need for evaluation techniques that can be used for the discovery and development of effective herbicides. Before the development and use of aromatic solvents, submersed aquatic weeds were usually removed mechanically. Mechanical removal is time consuming and costly and contributes little toward lasting control or eradication of the weeds. Recently, a number of herbicides that provide some degree of control have been developed. Many of these materials, however, are toxic to irrigated crops and to fish and other wildlife, and the control period is short. The evaluation techniques reported here were designed for use in the discovery and development of new and more efficient herbicides.

Witchweed, which parasitizes corn, sorghum, sugarcane, rice, and many other members of the grass and sedge family, was found in 1960 on approximately 167,000 acres of crop land in North Carolina and South Carolina. In 1957, the first year of field studies with witchweed in the United States, there was a general opinion that herbicides would never be feasible for its control. However, Figure 1 shows that witchweed-infested land will respond to methyl bromide, although the cost is prohibitive for field applications.

The evaluation of herbicidal weed control is often difficult, time-consuming, and non-precise. Neither weed counts, weights, ratings, effects on labor requirements, nor other common methods are wholly satisfactory for general use, although most of these methods are of value for one or more specific purposes.

Porter, et al. reported promising results for the use of N–(3,4–dichlorophenyl)methacrylamide (referred to in this paper as (DCMA) as a potential post-emergence herbicide for cotton. These workers found when sprays of DCMA were semi-directed under cotyledons of young cotton, satisfactory weed control could be obtained with little injury to the cotton.

In a previous paper it was reported that there was no difference in the oxidation of ascorbic acid by homogenates from control and N–(3,4–dichlorophenyl)methacrylamide (referred to in this paper as DCMA) treated corn tissues until 3 to 4 days after treatment. At this time, there was a sudden increase in the oxidation of ascorbate by homogenates from treated tissue. The rate of oxidation continued to rise throughout the testing period (0 to 8 days after treatment). Since this appeared to be a significant finding, it was decided the reaction should be pursued further.

On the rich alluvial soils of the Mississippi Delta it is not uncommon for Johnsongrass (Sorgum halepense (L.) Pers.) to spread over entire plantations. Eradication is not feasible, and adequate control in the Delta areas is accomplished only by the diligent use of control practices.

Johnsongrass (Sorgum halepense (L.) Pers.) is a serious problem in many parts of the United States but little is known about the carbohydrate metabolism of this weed. Rapp studied the seasonal variation of various carbohydrates in Johnsongrass grown in pots. These plants were placed in the greenhouse for several weeks. The purpose of the present investigation was to study carbohydrates in field-grown plants and to obtain information on the effects of herbicidal treatments on the carbohydrate balance.

The behavior of highly volatile pre-emergence herbicides in soil and their relative availability to plants under various conditions is poorly understood and pertinent information is much sought after by workers in chemical weed control. Ashton and Sheets reported an inverse relationship between injury to oats and soil adsorption of ethyl–N,N-di–n–propylthiolcarbamate (EPTC) in various soil types. Later, Sheets demonstrated a close relation between the initial toxicity of EPTC and soil types. EPTC was inactivated about one-third as rapidly in an autoclaved soil as in a corresponding unautoclaved one, from which he suggested that microbial breakdown may be a major pathway of EPTC inactivation when the chemical is incorporated in the soil.

Monuron [3–(p–chlorophenyl)–1,1–dimethylurea] is reported to be a potent inhibitor of the Hill reaction by Cooke and Wessels and van der Veen. It is reported to be 125 times as active as phenylurethan [ethyl–N–phenylcarbamate] in inhibiting the Hill reaction. Diuron [3–(3,4–dichlorophenyl)–1,1–dimethylurea] is 2500 times as active as phenylurethan as a Hill reaction inhibitor. Monuron and diuron have been used in photosynthetic studies. There are no reports in the literature indicating a difference in the mode of action of these compounds.

2–chloro–4,6–bis(ethylamino)–s–triazine (simazine) is a highly selective herbicide. Corn (Zea mays) is very resistant to the toxic action of this compound while wheat, (Triticum spp) and oats (Avena spp) are susceptible.

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.

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.

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 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.

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.

Yellow nutsedge (Cyperus esculentus L.) is one of the most serious weeds in New York State. This weed has an extensive distribution in the state where it is a strong competitor with row crops especially corn, beans, and potatoes. Nutsedge is also an important weed problem in many other leading agricultural areas of the United States. The problem in all of these areas has increased recently, possibly due to a reduction of competition from other weeds which are being satisfactorily controlled by selective herbicides.

The wild oat (Avena fatua L.) is one of the most common annual weed species in the northern portion of the great plains region of North America. It has been estimated that up to 70 bushels per acre of wild oat seeds occur in the soil of seriously infested fields. As an impurity in threshed grain it frequently amounts to 10 per cent or more as dockage. To become a serious problem under the climatic conditions and cropping practices of this region, the seed of an annual weed such as wild oats must undergo a period of dormancy and require exacting conditions for its germination. Therefore, investigations to study the factors affecting dormancy and the optimum conditions under which weed seeds will germinate have received considerable attention.

The use of herbicides in inter-tilled crops may reduce the number of cultivations necessary for weed control. Thus, in soybeans, how many cultivations are needed when herbicides are used in bands over the row? Overall?

Cyperus esculentus L., commonly called yellow nutsedge, is a perennial sedge. The single culms, 2 to 9 cm tall, have at the base a swelling termed a basal bulb. Short, weak rhizomes terminate in tubers.

Crabgrass, Digitaria sanguinalis (L.) Scop., is one of the most troublesome annual turf weeds over much of the United States. In the sub-tropical climate of Southern California its life cycle appears to be quite different from that in most of the United States. To the author's knowledge, its behavior in such a climate has not been described. Studies of its natural development here were conducted in 1959 and 1960.