Lack of seedling vigor is a serious limitation to obtaining adequate stands of birdsfoot trefoil (Lotus corniculatus L.). Slow seedling growth makes establishment difficult because competition from weeds or companion crop plants often eliminates the young legume seedlings soon after they emerge. Gist and Mott found that birdsfoot trefoil grows much more slowly than alfalfa and red clover under identical light intensities. Seedlings not eliminated are greatly reduced in size and are susceptible to injury during the winter.

The new scientific discipline, weed control, is the product of research. So long as man has grown crops for his own personal use, he has fought weeds, for nature favors community life for her plants. True there are examples of pure cultures of plants in nature; the white pine forests of the northwest, the buffalo grass prairies, wild rice in the northern lakes. But by and large, the areas now devoted to our major crops, wheat, corn, cotton and forage, were occupied by mixed plant populations and now they are in monoculture or in controlled plant populations and this nature abhors. Hence through the ages and even more today the farmer has been at war with weeds, the invaders of his crops.

The use of 2,4-dichlorophenoxyacetic acid (2,4-D) to control annual weeds such as pigweed (Amaranthus retroflexus L.) is common. Abundant evidence has been published to show that 2,4-D affects germination and subsequent seedling development. Allard et al. found that 2,4-D delayed germination and caused abnormalities in seedlings of 22 broadleaf and cereal species. Elongation of radicles was inhibited in mustard seedlings and in both non-dormant and embryo-dormant seeds as well as in seeds with impermeable seed coats. Germination can not only be delayed but can be inhibited, although at low concentrations of 2,4-D germination may be accelerated. Leachates produced by rainfall coming in contact with 2,4-D in soil were deleterious to seeds of flax and corn. To explore further the effects of 2,4-D on seeds, germination tests were made with scarified and nonscarified seeds of pigweed and on the effect on yield and germination of seeds harvested from pigweed plants that were sprayed with sublethal doses of 2,4-D in field plots.

One of the most marked effects of herbicidal concentrations of 2,4-D (2,4-dichlorophenoxyacetic acid) is the swelling and proliferation of basal stem tissues. Sell et al. reported a large increase in the protein content of stems of bean plants treated with 2,4-D. Shaw, et al. observed an increase of total protein in plants treated with 2,4-D and Rebstock, et al. found the nucleic acid content to double in the stems of bean plants treated with 2,4-D. Rebstock et al. postulated that nucleic acid was involved in the unusual growth and development of the plant. Skoog has presented an attractive hypothesis linking auxin action with nucleic acid metabolism. Current biochemical investigations leave little doubt that RNA (ribonucleic acid), particularly of the microsome fraction of the cytoplasm, is involved in protein synthesis. Furthermore, RNA appears to be implicated in oxidative phosphorylation and ion absorption, two processes known to be affected by 2,4-D.

Shortly after 1934 when Kögl and co-workers found that indole–3–acetic acid is a substance which has cell elongation activity in plants, many attempts were made to find other chemicals showing an indole–acetic–acid-like activity. It is 25 years now since Zimmermann and Wilcoxon found that naphthyl–1–acetic acid and some other aryl-acetic acids are active plant regulating compounds also. With these experiments it could be shown that the indole-nucleus is not essential for a plant growth regulator. The findings of Irvine showed that 2-naphthoxy-acetic acid is equally active as a phytohormone. This indicates that the acetic acid has not necessarily to be linked to the naphthalene ring directly. Thenaphthoxy-acetic acid was further modified chemically and became the starting point for the most widely used phytohormones: 2,4-D, MCPA and 2,4,5-T.

As reported in the previous paper, 2,4-D (2,4-dichlorophenoxyacetic acid) caused marked changes in the RNA (ribonucleic acid) content of seedling stem tissue, particularly in the microsome fraction. The ribonucleoprotein particles of the microsome fraction participate in protein synthesis and any abnormality in their metabolism could conceivably result in biochemical and physiological disorders leading to the death of the plant.

Sodium 2,2-dichloropropionate (dalapon) has been one of the more successful herbicides in controlling grass type weeds that have an abundance of underground rhizomes such as Johnsongrass (Sorgum halepense) and quackgrass (Agropyron repens).

Halogeton (Halogeton glomeratus) is an introduced, poisonous annual plant which is rapidly invading the salt-desert ranges of western North America. The poisonous constituent of this plant is water-soluble oxalic acid, which varies from 17 to more than 30 percent of the dry weight in its leaves during the growing season. Because of the poisonous property of halogeton and its dense population on disturbed site, it is of considerable importance to the livestock industry.

Because all agricultural chemicals applied to plants eventually reach the soil, and because many herbicides are applied directly to the soil for absorption through plant roots, it is desirable to test the persistence of these reagents in soils of varied types. Many such tests have already been conducted. Additional studies will be necessary as new phytotoxic chemicals are discovered. In this paper tests on some of the herbicides which have been studied during the past decade are described. Most of these herbicides are already in extensive use and much information has already been obtained relative to their reaction in soils. The data included here are submitted in an effort to round out the available information, particularly as related to long time effects of the herbicides in soils.

Alarge proportion of the commonly used herbicidal substances were derived from that class of organic compounds somewhat loosely known as the substituted phenols. Many of these compounds, as well as their close relatives, have been reported to affect cell division in a number of ways. Since there appeared to be some confusion as to the type or types of effect as well as to the similarities between the effects of different members of the group, comparative studies of a number of compounds were undertaken. Two questions were considered: 1. are the cytological effects such as to suggest subtle biological hazards to organisms apparently not affected morphologically; and 2. is there a family resemblance in the cytological reaction category? Although neither question has been answered satisfactorily, the results of our studies to date are sufficiently suggestive to warrant reporting.

It is indeed a real pleasure for me to have the opportunity to participate in this third meeting of the Weeds Journal of Weed Society of America. The years I spent in the Weed Investigations Section were among the most rewarding of my professional life.

The small size and slow growth of legume seedlings make them susceptible to damage or elimination by weed competition. Various methods of establishment such as sowing in late summer, sowing with a small grain companion crop, or mowing have not been entirely successful. The increased use of weed-controlling chemicals has awakened considerable interest in the establishment of legumes with the aid of herbicides. Research workers are in agreement that 4-(2,4-DB) [4-(2,4-dichlorophenoxy)butyric acid] can be safely used to control broad-leaved weeds in legumes. However, there is some difference of opinion as to the rates of various formulations that can be safely used.

Need for reliable information concerning the effects of environment on the response of plants to herbicides motivated the construction of the controlled environment system described herein. A unit suitable for such studies should have these general specifications: 1. a useful range of control of light, temperature, and relative humidity; 2. no recirculation of air, to avoid overall contamination of the unit by volatile herbicides; 3. capability of maintaining several sets of conditions simultaneously; and 4. a design which may be modified easily. The system described was constructed with these points in mind.

It has been recognized for some time that although short-chain alkyl esters of 2,4-D are very toxic, they do not translocate so well as the parent acid or the heavy esters. Two very plausible reasons for this are apparent: (1) These compounds, being highly lipoid soluble, dissolve readily in plant cuticle, and other lipoid phases, and tend to be held in this phase; (2) penetrating rapidly, these compounds are highly toxic to the treated leaves. This contact toxicity kills the mesophyll and fine vascular bundles of the leaf and stops translocation.

It is a great privilege and a pleasure to have this opportunity of discussing with you the status and organisation of research and development work on weed control in Great Britain. We have followed with keen interest the formation and growth of your “Weeds Journal of Weed Society of America” and have greatly enjoyed papers from your secretary, Dr. Warren Shaw, and your past president, Dr. Bob Beatty, at our own British Weed Control Conferences. Your immediate President is an especial friend of ours and it was while he was working with us in Oxford two years ago that he received intimation of his election to this post.

The use of herbicides for controlling weeds in the grape row is becoming resolved in mature vineyards. Oil and DNBP mixtures can be used because of the protective covering of old bark on the trunk. Herbicides such as CIPC, monuron and diuron can be used as a band treatment in the row because of the resistance to these chemicals where only a portion of the root zone is treated. Most of the above references caution about the use of these materials on young vineyards or transplants.

The use of various arsenic compounds as herbicides to control undesirable vegetation, reducing fire hazards and allowing convenient access, has long been recommended.

The great herbicidal developments of recent years give hope for chemical control of annual bluegrass, Poa annua, which is a major weed problem in bentgrass turf. Annual bluegrass produces an abundance of seed and quickly dominates bentgrass turf that is not growing at its optimum. Annual bluegrass might be controlled by prevention of seed set, pre-emergence control, and plant eradication. The original purpose of this study was to evaluate chemicals which offered promise of annual bluegrass control by checking seed set. However, necessity led to consideration of any promising chemical regardless of its method of control.

The efficiency of cotton production has been materially increased since 1949 through the use of several pre- and post-emergence herbicides. In the high-rainfall areas, combinations of a pre-emergence herbicide such as isopropyl N–(3–chlorophenyl)carbamate (CIPC) or 3–(3,4–dichlorophenyl)–1,1–dimethylurea (diuron) with one of several post-emergence oils have given more dependable control than the use of single herbicides. In the irrigated areas, early-season weeds have been less of a problem and more attention has been given to herbicides for the control of late-appearing grasses and vines. The substituted ureas, 3–(p–chlorophenyl)–1,1–dimethylurea (monuron) and diuron, have been the most successful herbicides for this use.

It gives me a great deal of pleasure to have been asked to talk on the subject, “A Conference Was Born”. Before going into the birth of the first conference I would like to give some history which had much to do with the first weed control conference.