Amitrol (3-amino-1,2,4-triazole) has received considerable attention in recent years as a herbicide and defoliant. This material was noted to have growth-inhibiting and defoliating properties by Hall et al. in 1952. Hall et al. reported that amitrol caused chlorophyll destruction under certain conditions and that chlorophyll synthesis was impaired in tissues formed at the time of, or subsequent to, absorption of the chemical. These workers also reported that cotton treated with amitrol showed a loss approximately 50 percent of the original reducing sugars and sucrose. Herbert and Linck have reported an initial increase in the rate of respiration of Canada thistle following treatment with amitrol. This initial respiratory increase was followed by a decrease which was dependent upon time as well as the concentration of amitrol applied to the plants. Similar results were obtained by Miller and Hall using Avena sections and cotton leaf discs. Heim et al. found that amitrol caused decreases in catalase activity of certain plants. Reduction of chlorophyll content and catalase activity were obtained following application of amitrol to leaves of potato, barley, and sunflower. In experiments reported in a more recent paper by these workers, amitrol caused in vitro inhibition of catalase activity.

Witchweed (Striga asiatica), a parasitic plant with brilliant-red flowers and hairy bright-green stems and leaves, was identified in the Western Hemisphere for the first time in 1956, although it had been present in the United States for several years. Figure 1 shows severe corn damage caused by witchweed. In a 1959 survey conducted by the United States Department of Agriculture witchweed was found on approximately 250,000 acres of land in 15 counties in North Carolina and 7 counties in South Carolina. It attacks many species in the family Gramineae. Witchweed jeopardizes the production of corn, sorghum, sugarcane, and probably other gramineous crops in any climatological regions of the United States where it may be adapted. This study attempted to obtain some indication of the possible limits of its spread.

4–Chloro–2–butynyl N–(3–chlorophenyl)carbamate (S–847) has been reported to show promise for selective control of wild oats in wheat, barley, flax, sugar beets, and peas. This paper presents data on the influence of several treatment conditions on wild oat control.

One of the important areas of current herbicide research is the investigation of herbicide mixtures. It is a common field experience that use of a single material—even of a “broad-spectrum” herbicide—exerts a selective pressure on the field population because of differential effectiveness on the various weed species. There is some evidence that a part of this derives from purely mechanical considerations (e.g., the spraying system in use may not reach plants of different growth habit equally well), but in any case the weed control program often appears to decrease in effectiveness after several seasons. In addition to favoring the survival of particular species, the non-eradicatory application of even a highly efficient chemical apparently aids in the establishment of populations of individuals which are physiologically most tolerant of the herbicide used. It will probably be granted, then, that the use of mixtures of toxicants will provide more effective control of populations of mixed weed species, and may also reduce the numbers of individuals and species exceptionally tolerant of the herbicide program, especially when the toxicants kill by affecting different physiological processes.

In considering the interaction between microorganisms and herbicides applied to the soil, two effects may become of great practical significance. One involves the potential inhibition or even germicidal action of the chemical to the microscopic inhabitants of the soil. These organisms, chiefly the bacteria, fungi and actinomycetes, occupy a unique position in biological cycles in terrestrial habitats and are essential for plant growth and soil fertility. The microorganisms decompose root and crop residues, mobilize the reserve of organic nitrogen and phosphorus, carry out transformations involving a change of oxidation state and bring about many other reactions necessary for crop production. Any deleterious influence, even of a temporary nature, could have a profound effect upon crop yields.

Since isopropyl N-(3-chlorophenyl)carbamate (CIPC) is being recommended for use on a limited acreage to control barnyardgrass (Echinochloa species) in drilled rice, it was of interest to the author to investigate the mechanism of selectivity involved. Although a difference in sensitivity among graminaceous plants to isopropyl N–phenylcarbamate (IPC) and CIPC has been recorded, the author was unable to find any explanation for this difference. Observations in the field indicated that Echinochloa seedlings were killed regardless of the depth at which the seed was located; whereas, most rice seedlings escaped injury if the seed was planted sufficiently deep. There appeared to be, however, a difference in response among varieties of rice. The following investigation was initiated to explain the differential response among varieties; however, the conclusions were expanded to explain the selective mechanism for controlling barnyardgrass in rice. The data presented in this paper are representative of results obtained in a series of experiments on this subject.

The present experiments were part of a study to determine the mechanisms by which herbicides affect plant growth and to find metabolites which protect growth against the inhibitory actions of herbicides. Bakers' yeast was selected for use in preliminary investigations because its rapid growth rate facilitates examination of large numbers of herbicide-metabolite combinations. The experiments reported herein present evidence which implicates histidine metabolism as a growth process which is sensitive to 3-amino-1,2,4-triazole [amitrole].

Arsenic-containing compounds have been widely used in the field of weed control. Sodium arsenite has been employed for general contact weed control, and as a herbicide on turf areas. In the latter capacity it is used to control undesirable species without inflicting severe or permanent injury to desirable turf grasses. Disodium methylarsonate (DMA) and dimethylarsinic acid (cacodylic acid) have more recently been shown to possess herbicidal properties. DMA has been used for the selective control of crabgrass in turf, and for removal of certain weedy species from Bermudagrass.

Investigations during the past three decades have confirmed that field bindweed (Convolvulus arvensis) is exceedingly difficult to eradicate. Since the introduction of sodium chlorate by Latshaw and Zahnley various other soil sterilants have been used successfully for spot treatments. Timmons reported the effect of various systems of intensive cultivation on bindweed control as influenced by root reserves. Phillips and Timmons reported the response of bindweed to crop competition and combinations of cropping, cultivation and 2,4-D. The introduction of 2,4-D (2,4-dichlorophenoxyacetic acid) provided a new tool for bindweed control and an impetus for continued research.

The table briefly summarizes research findings involving the translocation of organic herbicides and certain selected growth regulators in higher plants. Gibberellic acid, indoleacetic acid, naphthaleneacetic acid and other “on-herbicide” growth regulators are for the most part not listed except when used in experiments with the more generally accepted herbicides. For tabular information on translocation of auxins and other growth substances, the reader is referred to the Handbook of Biological Data, mentioned later. Information in the table is based on techniques which primarily utilize foliar application and for the most part does not include application via root system, injection, or bark application. As a consequence, most substances listed may be assumed to be transported predominantly in the phloem, but in numerous cases the compounds also move into the xylem.

The potential extensive use of certain new herbicides has made it desirable to study their effects on soil microorganisms. If these compounds have any retarding or stimulating influences on the general soil microflora, this could be reflected in carbon dioxide evolution during soil respiration experiments. Microorganisms are important to soil fertility because they transform potential plant nutrients into active or available forms, and carbon dioxide is a significant index of their activity. The effects on carbon dioxide evolution of four new herbicides that have shown promising results in field trials at this station are presented in this report.

The physical adsorption of chemical substances onto surfaces in soils or inside plants has been of considerable interest with respect to the fate of herbicides in soils, the selectivity of growth regulator herbicides, and even with respect to the toxic activities of growth regulators in plants. Comparative measurements of the adsorption of various herbicides are limited in number and scope. Experiments are presented here which attempt to measure the relative adsorptive qualities of various chlorinated phenoxyacetic acids, and to provide some evidence concerning the bearing of adsorption on herbicidal action.

The cotton-producing industry today faces a real challenge in its attempt to control weeds in cotton. It is a problem with many facets. Differences in weed species, topography, soil type, scale of operation, rainfall, and many other factors make it difficult to develop single practices that work satisfactorily across large areas of the Cotton Belt.

One of the major characteristics limiting the usefulness of pre-emergence herbicide applications concerns the persistence of chemical activity in the soil. In many instances, the herbicides break down too quickly to obtain satisfactory weed control. On the other hand, there is the possible hazard that a chemical may be too persistent and thus endanger the growth of succeeding crops. Another closely related factor is susceptibility to leaching. It is especially important when chemicals are used that are toxic to the crop plants as well as the weeds.

Canada thistle was named Carduus arvensis by Tabernaemontanus in 1687, Cirsium arvense by Tournefort in 1700, Serratula arvensis by Linné in 1753, Cirsium arvense by Scopoli in 1772, Carduus arvensis by Robson in 1777 and Cnicus arvensis by Hoffman in 1804. The name Cirsium arvense Tourn. was adopted, but more recently Canada thistle has been referred to as Cirsium arvense (L.) Scop. The cardinal number of chromosomes for the Cirsium genus is 17.

Rhizome initiation and growth is a contributing factor to the problem of controlling Johnsongrass (Sorgum halepense (L.), Pers.). Control methods by intensive cultivation or chemical applications are directed primarily toward the destruction of these underground structures. As described by Fletchall et al. rhizomes are fleshy, segmented underground stems having scales at the nodes. Their development is rapid; they function as organs for carbohydrate storage, and as reproductive structures which produce vegetative shoots from axillary and terminal buds. Information relative to development of rhizomes and their response to various treatments is reported; this is essential to understanding and evaluating methods of control.

The outstanding success of 2,4-D as a selective herbicide stems from the great susceptibility of many broadleaved (dicotyledonous) weeds to the compound. Applications of 2,4-D which will eliminate many dicots will leave most grass crops relatively unaffected. Several suggestions that have been made for the differences in susceptibility between grasses and broadleaved weeds, including differences in foliar absorption, restricted translocation of the compound in grasses, and differences in detoxification of the 2,4-D molecule.

Annual weeds have always been a problem to the cranberry grower, but certain changes taking place in the bog environment have caused an increase in the population of annual weeds in some areas in recent years. The decline of soil acidity as a result of the long term use of alkaline water for frost flooding, coupled with the well drained bog culture recommended for Wisconsin growers, have produced an environment to which certain annual weeds are adapted. With some species, particularly common ragweed (Ambrosia artemisiifolia), the extensive use of petroleum products as herbicides has encouraged the invasion of annual weeds following the suppression of oil sensitive perennials.

The chloro-substituted benzoic acids discussed in this paper have been evaluated experimentally as soil sterilizing herbicides for field bindweed (Convolvulus arvensis L.) control at the Ft. Hays Experiment Station since 1955. The value of soil sterilization in a perennial weed control program in the Great Plains region is evidenced by recommendations made by several state experiment stations. Prior to 1950, most semi-permanent soil sterilization was accomplished with such chemicals as sodium chlorate, boron compounds, and arsenicals. These compounds continue to be important even though the poisonous qualities of arsenic compounds and the hazards of handling sodium chlorate are well recognized.

This report describes the preparation, purification, and properties of 18 new herbicides, amino acid derivatives of 2,2-dichloropropionic acid (dalapon) and 2,3,6-trichlorobenzoic acid (2,3,6-TBA). The biological evaluation of the compounds as selective herbicides is being made by other investigators and will be published later. Some of the compounds are also being evaluated for nematocidal, fungicidal, and anticancer properties.