In the field of weed control a great deal of attention is being given to the control of weeds after they germinate; in other words, pre- and post-emergence weed control. Control of dormant weed seeds in the soil has received little attention except in seedbed fumigation and in turf renovation. Many of the fumigant type materials were selected and screened for the control of nematodes and soil-inhabiting insects. It was discovered that some of them will control dormant seeds as observed by reduced weed stands as compared to non-treated areas.

Evidence that β-alanine or calcium pantothenate partially reversed the inhibitory action of several chlorinated aliphatic acids on yeast growth (4) suggested the hypothesis that synthesis of pantothenate is one of the metabolic pathways sensitive to this group of herbicides. The objectives of the experiments reported herein were (a) to determine the mechanism by which the enzymatic synthesis of pantothenate was inhibited by these compounds, (b) to seek evidence for the contributions of this mechanism, in vivo, to the herbicidal effects of 2,2-dichloropropionic acid (dalapon), (c) to determine whether pantothenate treatments could overcome the effects of dalapon in plants and (d) to test chloro-substituted analogs of pantoate for herbicidal activity. To achieve the last objective it was necessary to synthesize several new chemicals.

Most of the evidence for the production of toxic substances, by one plant, that affect the growth and survival of another, is circumstantial, according to a review by Bonner (5). There is direct evidence that the leaves of Artemisia absinthium L. (3), Encelia farinosa A. Gray (6), and Thamnosma montana Torr. & Frem. (2), produce substances which are toxic to other plants. A substance has been isolated from the roots of guayule which is toxic to guayule but which is unimportant agriculturally because this substance remains only a short time in the soil (4). Also dead brome grass roots have been found to be toxic to brome seedlings (1); however the evidence here is indirect (5). Le Tourneau et al. (13) have shown also that water extracts from tissues of many crops and weeds inhibit germination of wheat.

Oxalic acid and oxalates occur in many plants. Consumption of plants containing high concentration of oxalates can be poisonous to animals. This has been reported by several investigators (5, 7, 9). However, in only a few plants are oxalates found in sufficient quantities to be lethal. Some species with a relatively high oxalate content are: sorrel (Rumex spp.), rhubarb (Rheum spp.), greasewood (Sarcobatus vermiculatus Torr.), soursobs (Oxalis cernus Thunb.), and halogeton (Halogeton glomeratus C. A. Mey.).

Wood (13) has estimated that 61,000,000 acres, or 60 per cent of the cropped land of the Great Plains region of North America, are infested with wild oats, Avena fatua L. The wide-spread seriousness of this weed and the fact that there is no cropping or tillage practice known for its ready control, point out the importance of finding a feasible chemical method.

The increasing use of toxic agents as pesticides for application contiguous to water areas has been viewed with trepidation by many fisheries workers. Herbicidal chemicals are viewed with particular alarm due to their increased use, both present and projected, for the control of aquatic vegetation where they are placed in direct contact with fish and other aquatic organisms.

Johnson grass (Sorghum halepense L., Pers.) is a native of the Mediterranean coastal countries and was introduced into the United States about 1830 by Governor Means of South Carolina (5). About ten years later some seed was planted in fertile river bottom soil near Selma, Alabama, by Colonel William Johnson. As Colonel Johnson was the first person to cultivate the grass extensively in the United States, it was named for him. Since that time, the grass has been intentionally cultivated and unintentionally disseminated in many areas of this country. A recent distribution map by Hitchcock (3) shows that the plant may be found in all but about a dozen northern states.

Weed problems in Alaska are relatively new because man's agricultural activities in this region have been limited until very recently to isolated clearings. These early clearings made by prospectors and homesteaders to produce feed for their stock also unintentionally served as increase plots for some troublesome weeds.

The girdling of apple trees by field mice (Microtus spp.) is a common problem in most areas where this fruit is grown. Since these species of mice will seldom cross a bare area to feed, it is desirable to remove all vegetation at the base of the trees to help reduce the possibility of girdling. Many growers maintain such a bare area by slow and costly hand methods. Such methods are frequently employed in late fall, increasing the possibility that the newly exposed trunk area may incur winter injury.

Johnson grass (Sorghum halepense L.) is one of the most troublesome weeds in the United States. Since its introduction into the Southeast in 1830, this weed has spread to a total of 38 states. The perennial habit of Johnson grass contributes to its widespread geographical distribution and enables it to survive moderately severe winters. In addition to fleshy rhizomes, Johnson grass is usually a prolific producer of viable seed which may give rise to reinfestations after the established plants are controlled.

In recent years weed research workers have begun to investigate the possibility of using herbicides for the selective control of wild oats (Avena fatua L.) in field crops. One of the first herbicides to show promise for the control of wild oats was IPC (isopropyl N–phenylcarbamate). Although this herbicide was effective on wild oats, only a few broad-leafed crops proved tolerant to it. More recently, another herbicide, CDAA (2–chloro–N,N–diallylacetamide), has been found to be effective in controlling wild oats without damaging corn and soybeans, and several field tests indicate that it may be used successfully in flax. To be effective both herbicides must be applied as pre-emergence or pre-planting treatments. They kill wild oats as the wild oats germinate, and consequently must be placed in the vicinity of the germinating seed if a good job of killing is to be done.

Since weeds in cranberry bogs cannot be successfully controlled by mechanical equipment, there has been considerable interest in chemical means of control. Among the chemicals that have been and are presently being used are iron sulfate, paradichlorobenzene, sodium chloride, sodium arsenate, sodium arsenite, copper sulfate, kerosene, and other herbicidal oils (2). All these chemicals have to be applied in relatively large quantities, which makes for a large per-acre cost of treatment and involves many problems inherent in the application of large quantities of materials. There is, then, considerable interest in a chemical which can be applied in relatively small quantities and which will provide satisfactory control of weeds in the bogs.

The wild oat (Avena fatua L.) is considered to have spread originally from Asia; it is widely distributed throughout Europe and its advent in North America is attributed to introduction by immigrants from there (8, 13). The species presents a very serious weed problem in the prairie regions of Canada and northwestern United States (18). In Britain it has become prevalent in some regions as a result of intensive cropping to cereals (17). Up to 70 bushels of wild oat seeds per acre have been estimated to occur in the soil in badly infested fields in western Canada (12). This seed cannot all be stimulated to germinate by cultural practices and may remain viable in the soil for at least 3 years (4). The wild oat problem would be solved if the seed in the soil could be destroyed. There are two ways to achieve this: firstly, by stimulating the dormant seed to germinate so that the plants can be killed by cultivation or, secondly, by killing the dormant seed through the addition of toxic materials. Up to the present, attempts to do either of these have been unsuccessful; thus, investigations to determine the factors involved in dormancy are of primary importance.

The cranberry (Vaccinium macrocarpum) is a low growing, perennial, woody plant of the boglands of the northern United States. Because cranberries are grown commercially on wet, low lying soils, the fields are often infested with a wide range of weeds common to such areas. Among the most common weeds of Wisconsin cranberry bogs are (1) sedge family: Carex oligosperma, Dulichium arundinaceum, and Eriophorum uirginicum; (2) rush family: Juncus effusus and J. canadensis; (3) horsetail family: Equisetum arvense and E. fluviatile; (4) fern family: Onoclea sensibilis and Osmunda regalis; (5) water plantain family: Sagittaria latifolia; (6) grass family: Leersia oryzoides, Glyceria canadensis and Calamagrostis canadensis; (7) composite family: Ambrosia artemisiifolia, Bidens connata, and Solidago graminifolia; (8) primrose family: Lysimachia terrestris and L. thyrsiflora; (9) buckwheat family: Polygonum sagittatum and P. amphibium; (10) rose family: Potentilla palustris and Rubus hispidus; (11) mint family: Lycopus uniflorus and Scutellaria epilobiifolia; (12) St. Johnswort family: Hypericum uirginicum; (13) gentian family: Menyanthes trifoliata; (14) willow family: Salix nigra and Populus tremuloides. Many other weed species occur in cranberry bogs, but they do not present a serious cultural problem.

The present extensive use of herbicides in soil application has resulted in a great deal of interest in the breakdown of these chemicals in soil (1, 4, 6, 8). An increasing demand exists for information that will permit fairly accurate predictions of the residual life of these chemicals (4). The breakdown of chemicals in soil has been repeatedly shown to be the result of microbiological activity in part but other factors are also known to contribute to the disappearance (1, 4, 5, 7, 8, 9).

One of the major costs in the production of woody ornamentals is for weed control by cultivation and hoeing. In nurseries, plants are grown in the same location for two to five years, and several species often are grown in mixed blocks. Thus, there is a need for a herbicide which is non-toxic to as many species as possible.

The chloro-substituted benzoic acid compounds discussed here were included with a number of other chemicals tested in 1955, 1956, and 1957 as soil sterilizing herbicides at Hays, Kansas. The experiments were designed to yield information on the effectiveness of various treatments for field bindweed (Convolvulus arvensis) control. Results of the bindweed control studies have been briefly summarized by Phillips (9).

Studies of effects of weed competition on crop yields, and of procedures used in screening herbicides as to effectiveness for weed eradication, often require the planting of weed seeds under field or greenhouse conditions. Because of the many factors that contribute to delayed germination, field and greenhouse stands of weeds obtained in this way are often irregular and slow in developing. Although methods for obtaining laboratory germination of weed seeds have been worked out for many species the methods are not always applicable for field planting, particularly where removal of seed coats or use of alternations of widely different temperatures are advocated.

The commercial use of herbicides formulated on granular carriers has expanded rapidly and in many instances has preceded research on their development and properties. Experimental studies have been concerned primarily with field problems involving the control of weeds in a particular weed-crop situation. Conflicting results obtained in both the experimental and the practical use of granular herbicides have emphasized the need for basic information on the mode of action of granular-herbicide formulations and the effect of environment and cultural techniques on their use.

On rich alluvial soils where corn is the principal crop, Johnsongrass is the most serious perennial weed in Ohio at least as far north as the 40th parallel, and it has spread rapidly north of that area, even into southeastern Michigan. Many people still credit the statements of Piper (3), Vinall (6), and Bennett (1) that Johnsongrass behaves as an annual north of the 38th parallel. Pammel and King (2), to be sure, reported Johnsongrass as a perennial weed in southwestern Iowa in 1919 and the junior author's experience with it as a weed in Ohio, from the 40th parellel south, began in 1918. At Columbus these infestations have lived through winters in which the temperature was below 0° F for prolonged periods and the ground was frozen to a depth of 6 to 8 inches. There seems to be no hope for the eradication of Johnsongrass by mere freezing.