At the Third British Weed Control Conference in 1956 I had the pleasure to discuss weed control research and development in Sweden (3). Some of the statements I made at that time will be used as a background to this paper. It was emphasized that there has been continuous change in weed control methods since World War I depending on the introduction of chemical weed killers but also on improved methods for cultivating and using the lands. Use of chemicals have brought with it changes in the weed flora meaning that certain weeds which were not serious in earlier days have now become a menace to the farmers. This brings with it a need for new chemicals with other weed killing properties. But it also brings with it a need for new cultivating methods and a better crop sequence. Cultivated plants are influenced by the chemicals. The effect on the cultivated plants depends on the stage of development of these plants. In uneven fields the harmful effect can be serious as there are always some plants that are sensitive at the time of spraying. The effect of the chemicals may depend on the purity of the acids. In MCPA, for example, the percentage of the 4–isomer, i.e. the 2–methyl–4–chlorophenoxyacetic acid, is important. It should be 95 per cent or slightly above as shown by åberg (1). The after effect of chemicals in the soils may be longer and more severe under northern conditions than under southern. For the choice of crops this must be considered. Thus there is no doubt that today, more than at any earlier period, weed control is a crop production problem. It can not be treated without considering crop production problems. Sometimes there is a feeling over in our part of the world that since the end of World War II chemicals and their properties have been emphasized too much in weed control discussions. Chemicals are, no doubt, important, but they can never get the place they are entitled to, unless our research work in weed control pays attention also to biology and ecology of those plants that we treat; cultivated plants as well as weeds. I believe we are in Europe thinking more about this particular end of the weed control work than you need to do over here. We usually have small farms with a number of different crops on each one of them. Thus we must learn to apply our chemical weed killers or use our cultivated methods in different ways for each one of these crops. For economical reasons and with regard to the supply of food and feed we need high yields per hectare. Every measure on a farm must be chosen with this in mind. Our problems, progress and organization of weed control must then be seen against the background I have now tried to give you.

I feel greatly honoured to have been invited to cross the Atlantic to address so distinguished a gathering in the weed research and control fields.

Not more than 5 years ago the subject of herbicide residues on food probably would not have aroused too much interest. Such is not the case today. Aware as you are of the improvement in agriculture practice that can stem from herbicide usage, you doubtless are also familiar with the associated residue problem. My purpose this morning is to comment on some aspects of that problem from the standpoint of recent legislation.

The plant growth regulating properties of 2,4–D (2,4–dichlorophenoxyacetic acid) (26) and the resistance of most monocotyledonous plants to the toxic effect of this chemical (17) have been known for many years. This difference in sensitivity of various species to the toxic effects of 2,4–D has had wide practical use in the field of weed control. However, there is no generally accepted mechanism for the selectivity between sensitive and resistant plants or for the actual mechanism of 2,4–D action. The four areas of research which have been investigated to elucidate the mechanism of action are absorption, translocation, and two distinct metabolic approaches. Absorption and translocation are often studied simultaneously. Metabolism is studied from two approaches, either the fate of 2,4–D in the plant or the effect of 2,4–D on plant metabolism. All of these processes are operating simultaneously in the plant and the ultimate explanation as to the mechanism of 2,4–D action must incorporate all of the contributions from these areas of research.

In 1954 the authors reported studies involving the application of sodium 2,2–dichloropropionate (sodium salt of dalapon) to wild oats (Avena fatua) and concluded that treatment in the boot stage showed no promise in controlling viable seed production in wild oats. However, a lag in germination in seed from treated plants was noted in some instances (1). When seeds from these plants were planted in the greenhouse, many seedlings reached the coleoptile stage only, and failed to develop further (2).

Sorghum is second only to wheat in importance in dryland crop production in the Southern Great Plains. Sorghum is planted during the season when several common annual weeds normally emerge. Proper pre-planting cultivation will often reduce the seriousness of weed infestations, but many times the crop is invaded by weeds. Under such conditions chemical weed control is of value. These studies were initiated to determine the effect of 2,4–dichlorophenoxyacetic acid (2,4–D) on the yield of weed-free sorghum.

A relationship has been noted between environmental conditions, including soil characteristics, and the movement, persistence and activity of herbicides applied to the soil. Field studies have often given differing, and sometimes contradictory results, possibly because of different environments. Empirical studies cannot fully explain these differences.

Only a few reports have been published on the susceptibility of rabbitbrush (Chrysothamnus spp.) to chemical herbicides (1, 2, 5, 6, 7). From these publications the following conclusions may be made: (a) 2,4–D (2,4–dichlorophenoxyacetic acid) is more effective on rabbitbrush than 2,4,5–T (2,4,5–trichlorophenoxyacetic acid), (b) June applications are generally best, (c) rabbitbrush is more tolerant to growth regulators than big sagebrush (Artemisia tridentata), and (d) resprouting from the stem base is common.

Increasing the forage yield of rangeland by controlling big sagebrush (Artemisia tridentata Nutt.) with fire, chemicals, or mechanical means has become a common procedure. The main problem confronting researchers has been the remarkable ability of sagebrush to re-establish itself after a control program. Fire and mechanical means of control have proved to be effective in killing established sagebrush. However, a heavy stand of young sagebrush often becomes re-established within a few years (3). Since the use of chemicals for sagebrush control has developed within the last decade, very little is known concerning the re-establishment of the plant in chemically controlled areas.

Weed control constitutes one of the principal costs of onion production on muck soils. It has been estimated that cultivating and weeding make up nearly 40 per cent of the total labor cost in growing onions (5). The major component of this weed control cost is the hand labor required to remove weeds which come up in the onion row. During the past several years, research to find selective weedicides for onions and thus reduce weeding labor costs has been extensive.

The problem of herbicide volatility has been with us for several years, and promises to remain with us for some time. Mullison, et al. (4) in 1953 pointed out the reasons why physical measurements of herbicide volatility were impractical. Their arguments that the phenoxy herbicides generally have a low order of physical volatility and that analytical methods are insufficiently sensitive to measure the amounts of such herbicides which escape through volatility are still valid.

Interactions among the components of an herbicidal solution may take place (a) in the solution itself, (b) at the plant surface or within tissues to influence absorption and translocation, and (c) at the cellular site of toxic action. This broad meaning of the term interaction is employed in the present report. Similarly, the meanings of antagonism and synergism are considered as inhibition and enhancement, respectively, of the toxic action of one substance due to the influence of another, regardless of the location and nature of the interaction.

In many types of weed control experiments most economical progress can be made by visual rating of the plots. While such ratings are admittedly somewhat subjective, this does not necessarily mean that the results are less accurate or less satisfactory than methods which profess to be quantitative. For example, counting thistle sprouts in a square-rod area may show more sprouts in a treated plot than in the check because the herbicide used resulted in a number of weak sprouts replacing every strong sprout killed to the ground line. If only counts are made, the data will look as if no progress was being made, while if both the strength and number of sprouts are rated the actual situation will be much more nearly approximated.

It has been reported that the frequency of mowing lawns in some areas of the United States can be markedly reduced by the application of maleic hydrazide (3). Other investigators have reported a retardation of growth but no reduction in number of mowings and a scorched appearance (1, 2). To determine whether this practice is practical under tropical conditions, an experiment was conducted utilizing a number of important tropical lawn grasses.

The second General Business Meeting of the Weeds Journal of Weed Society of America (WSA) was held at the Hotel Peabody, Memphis, Tennessee, at 4 pm, January 13, 1958. The meeting was called to order by W. B. Ennis, Jr., President of the Society. He expressed his appreciation for the excellent work of the various Standing and Special Committees and especially for the full cooperation that he had received from the membership of the Society. He emphasized that the Society exists to serve the needs of the members, and that the ideas and suggestions of the members should be continuously solicited in an effort to improve WSA.

Edwin A. Davis has been appointed by the Crops Research Division, ARS, USDA, to conduct physiological studies related to control of chaparral in cooperative work with the U. S. Forest Service. Davis will be headquartered at Arizona State College, Tempe, Arizona.