The main factor determining the effectiveness of dinitro pre-emergence weed killers in the control of annual grasses and weeds is its distribution and concentration in the soil.

Chemical control of brush in right-of-ways is now a generally accepted practice. Through the recent period of development and ultimate successful use of this practice, certain important aspects of chemical control have been noted by those in the field of research and commercial use. Many of these aspects are amply documented in the literature while numerous common observations have never been recorded. In this general discussion of chemical brush control, an attempt is being made to weave both types of observations together.

In the past 10 years, phenomenal advances have been made in the regulation of plant growth by organic compounds including some now used as herbicides. The introduction of new chemicals, new weed-control techniques, such as pre-emergence treatment, and low gallonage application are among the most important recent developments in the use of organic compounds for weed control. It is estimated that losses caused by weeds on farms have now reached 5 billion dollars annually, and at present well over 30 million pounds alone of the phenoxy compounds, 2,4–dichloro, 2,4,5–trichloro-, and 2–methyl–4—chlorophenoxyacetic acids (2,4–D, 2,4,5–T and MCP) are being used for herbicidal purposes to help combat these losses (9). The most recent of these three compounds to appear on the market in this country as an active ingredient in herbicidal formulations is 2–methyl–4–chlorophenoxyacetic acid. The chief claim made for its use as a herbicide is that it is less injurious to certain grasses, cereal crops and legumes and more effective on certain weeds than 2,4–D. Fertig (4) concludes that MCP is slower in action and definitely less injurious to legumes, and Crafts (3) cites a number of investigators who have shown that MCP is more selective than 2,4–D, particularly where clover, flax and other crops having leaves hard to wet are concerned. High specificity of the compound is indicated by numerous reports in the literature; Robinson's (8), on the effectiveness of MCP in selective weed control, is one example. However, from recent recommendations (1), there appears to be some disagreement on the use of MCP, indicating need for further testing and experimentation with the compound and its derivatives. MCP as sold may contain up to 40% of impurities by weight, some of which, according to Hansen (6), may have toxic properties.

Research, education and regulatory work in the weed control field had much in common fifteen or twenty years ago. Few materials were then available for chemical weed control and a great deal of emphasis was placed on cultural methods. The regulatory man was doing extension work and the extension man in some states was doing regulatory work, assisting with or actually setting up weed districts, the overall objective, however, being control.

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.

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.

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.

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.

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.