A seed field of bolting onions is extremely difficult, if not impossible, to weed satisfactorily by hoeing or any mechanical means without serious reduction in seed yield, because of the ease with which seed stalks are broken. Injury to seed stalks results in lower seed yields, but if the weeds are allowed to grow they also reduce seed yields. The presence of weed seeds makes cleaning more difficult and may reduce yields further, because foreign material and weed seeds can rarely, if ever, be separated satisfactorily without the removal of some crop seed. Actually few, if any, commercial growers practice either cultivation or handweeding after the onion crop has begun to go to seed. Consequently, exceptionally weedy fields are common in onion-seed-growing sections. The use of herbicides as a possible solution to this difficult problem has been studied in Utah since 1949, with some promising results.

Weed control as we know it today is a new field with frontiers and relationships that have not been clearly charted. Weed control workers are, in a sense, pioneers. The background of knowledge is still not great and many of the questions our farmers are asking have no unequivocal answer. The sources of information are still not clearly defined and many agencies are involved in the search for information. Within any one university or college one frequently finds information that the weed specialist needs developing in the departments of botany, agronomy, vegetable crops, horticulture, chemistry and agricultural engineering. Commercial organizations of many kinds are discovering new facts that we need to know. And not the least of these sources of information is the Extension Service itself because county men, and the farmers they work with, are constantly adding to our knowledge. It is a dull man indeed who can view field after field treated to control weeds without arriving at a good working hypothesis of what can be done and how to go about doing it. The role of the Extension Service in the development of weed control over the past ten years has been overlooked in our emphasis on research. I would not for a moment minimize the importance of the emphasis on research but I do decry the lack of parallel emphasis on encouraging the use of the knowledge so developed. And the Extension Service in the many states has been a potent force in developing the new information credited to research.

During the course of investigation of the activity of some organic compounds selected for potential herbicidal effects (5), many candidates appeared to have activity equal to that of the standard 2,4–dichlorophenoxyacetic acid (2,4–D), while a few appeared to be more active. One of the latter was p–fluoro–o–toloxyacetic acid, which was first prepared by M. S. Newman (3).

An understanding of the physiological and morphological responses of plant tissues to phytotoxic compounds makes possible a more intelligent approach to the problem of selecting and developing new herbicides for the control of weeds in growing crops. This area of investigation is frequently neglected in the haste to screen the many new chemicals which are reported.

The First National Weed Control Conference can accomplish many things, not the least of which is further to dramatize the fact that weeds and their control constitute a major agricultural problem worthy of our best collective efforts and attention.

One of the most important of the numerous difficulties involved in the successful production of cotton is that of controlling weeds. The fertile soils and humid seasons generally occurring in the Delta, provide optimum conditions for abundant weed growth. During 1951, Missouri cotton producers spent approximately $10,000,000 for hand-labor alone in the production of a $69,000,000 crop. With the exception of Johnson grass (Sorghum halepense L.) and some perennial vines, annual weeds (particularly grasses early in the season), are most troublesome. By far the worst offender under the conditions of the 1951 through 1953 experiments was crabgrass (Digitaria sanguinalis L. (Scop.).

Promising results of applications of α, α-dichloropropionic acid (Dalapon) to wild oats (Avena fatua) were first reported in May 1953 in Dow Chemical Company's Dalapon Bulletin No. 1. Encouraging results with Dalapon on wild oats were obtained by various workers during the summer of 1953. The work reported herein was conducted in 1954 to gain further information on the effects of Dalapon on wild oats.

In reviewing weed control literature, papers are frequently encountered in which the data have been presented without statistical evaluation. It is important for research workers in the herbicide field to be able to estimate the validity of their comparison just as it is for the workers engaged in fertilizer studies or any other phase of field research. Arithmetic means presented alone in a graph or in a table are extremely difficult to evaluate. Even though the author of a paper may have confidence in the significance of his data, it is difficult for the reader of a research report to evaluate the conclusions if an estimate of the experimental error is not presented. This may seem to place undue emphasis on statistical analysis itself. Yet in the relatively new field of weed control, few workers have had sufficient experience to judge the significance of differences of varying degree.

The Southern naiad, Najas guadalupensis (Spreng.) Morong. is a submersed water weed commonly infesting water control systems in south Florida, especially in the areas underlain by calcareous deposits where the canal waters are mineralized. Dense growths of this plant appear to have become more prevalent in recent years following the removal of water hyacinths by the use of 2,4-D.

Numerous investigations in which crop plants were utilized to study the effect, persistence, and movement of spray residues of 2,4–dichlorophenoxyacetic acid (2, 4–D) in a variety of soils and under a wide range of conditions have been reported. However, except for a report by Arle (1), a search of the literature has revealed no direct information on the effects of 2,4–D when applied in irrigation water to crop plants growing in the field. Arle treated cotton with irrigation water containing 2,4–D in equivalents ranging from 0.5 to 8 pounds per acre. Significant decreases in yield usually resulted from the higher rates of treatment when applications were made early in the season. Applications at the lower rates usually resulted in yields about equal to or greater than those obtained from check plots.

In areas near oil refining centers, as in most of California, petroleum oils are widely used in agriculture. Reference is not made here to the use of petroleum to power and lubricate tractors and other farm machinery, but to its use as an agricultural chemical. There are three typical uses of oils: (1) insecticidal spray oils, (2) various oils as selective and general herbicides, and (3) solvent type oils as carriers for oil soluble agricultural chemicals. In California alone, annually from five to fifteen million gallons of petroleum oil are used for the control of scale, mites, and mealy bug (23). An estimated 10 million gallons of cracked gas oils are used for general weed control on canal banks, road sides, barnyards, and in orchards practicing non-tillage. Much solvent type oil is also used for selective weed control in umbelliferous crops, and for pre-emergence weed control in lettuce, beets, and onions. One large operator alone is using one million gallons annually. Aromatic fractions and fortified heavier oils are used as drying agents on flax, clover, and alfalfa seed crops and as cotton defoliants. DDT and other insecticides are commonly applied as dilute oil emulsions.

To those engaged in testing chemical compounds for herbicidal properties a troublesome problem is familiar, namely, what species or small group of species can best represent the reaction of many plants to a compound the potential of which is unknown.

Trials at the Everglades Experiment Station have shown that onions may be successfully grown in this area. The rich organic soil and the relatively long growing season of the crop present, however, a difficult problem in regard to the control of weeds. Weeds are very numerous and their rate of growth is exceedingly rapid. The problem is of such magnitude that the expense of hand weeding in closely spaced row crops discourages the farmer from undertaking the production of an otherwise potentially profitable crop. This study was undertaken to investigate the possibilities of weed control in onions in the organic soil of the Everglades using herbicides as both pre- and post-emergence treatments and determining their effects on yields.

Crabgrass, the universal lawn weed, has been the object of much research in the past few years. Lawn owners, cotton and vegetable growers, and golf course keepers have long been fighting this pest. Today, chemical eradication is rapidly displacing costly, difficult, and often ineffective mechanical control methods.

Shortly after we had completed several studies of the effect of the new herbicide, dalapon, (2,2–dichloropropionic acid), on enzyme systems, it became apparent that high concentrations of this compound inhibited a variety of different enzymes in a noncompetitive fashion. Furthermore, transparent solutions of enzymes frequently became quite turbid when this inhibitor was added. Such behavior suggested that 2,2–dichloropropionic acid was acting as a protein precipitant.

A number of portable spray systems have been designed for application of herbicides to experimental small plots. Several have been designed for special purposes or conditions which confronted the experimenter. Buchholtz, Robinson and Dunham, and Davis described portable small plot sprayers for use where the experimental areas were small or no gain in precision was found by using more than rod-row plots. In general these and other spray systems have some deficiencies, which are accentuated when the equipment is to be used in small plot experiments requiring a high degree of precision. The equipment described here (Fig. 1) was designed to spray plots 3′ × 18′ and smaller. If the plot size is greatly increased the utility of this unit in its present design is materially reduced. Other factors desirable for larger size plots have necessarily been sacrificed in order to enhance qualities deemed more essential for the precision small plot work.

Since it was first discovered by Bucha and Todd, that 3-(p-chlorophenyl)-1, 1-dimethylurea would kill most plants if applied at dosages of 20 pounds and above per acre there has been much speculation as to whether it is translocated in plants. Observations from early field trials indicating that soil treatments with this compound were more effective than foliar applications led to the assumption that entrance of the herbicide into plants was primarily through the roots. Loustalot demonstrated positively, however, that this substituted urea is also absorbed through the leaves and stems. Recent investigations at this laboratory, contrasting essentially equal applications on foliage and roots of several species, have also indicated that appreciable injury is caused by foliar absorption of the compound.