The search for means of controlling submersed aquatic weeds has emphasized the need for evaluation techniques that can be used for the discovery and development of effective herbicides. Before the development and use of aromatic solvents, submersed aquatic weeds were usually removed mechanically. Mechanical removal is time consuming and costly and contributes little toward lasting control or eradication of the weeds. Recently, a number of herbicides that provide some degree of control have been developed. Many of these materials, however, are toxic to irrigated crops and to fish and other wildlife, and the control period is short. The evaluation techniques reported here were designed for use in the discovery and development of new and more efficient herbicides.

For most effective weed control 2–chloro–4,6–bis(ethylamino)–s–triazine (simazine) must be applied to the soil. As a foliar spray it is much less effective. Simazine penetrates into leaves of some plants, but apparently the cuticle is a barrier to foliar absorption of this herbicide. It is absorbed rapidly by roots and is transported upward to the aerial plant parts.

The herbicidal effects of 2,4–dichlorophenoxyacetic acid (2,4–D) have been shown to be influenced by a number of factors. Among these are: (a) intensity of light before and after treatment, (b) stage of development and growth of the plant or tissues at time of treatment, (c) reserve carbohydrate supply, (d) temperature, (e) available soil moisture, (f) pH of the solution, (g) surface active agents, and (h) formulation.

In field practice much of the application of herbicides to local infestations of bermudagrass (Cynodon dactylon L.) is done by hand on a spray-to-wet basis. With a fixed concentration of active ingredient in the spray mixture the dosage is determined by the volume used in wetting a particular stand of grass. The amount of herbicide deposited on the weed foliage may be affected by the addition of surfactants to the spray mixture. In orchards and vineyards where the tolerance of the crop to the herbicide is limited, variations in the stand may lead to local overdosage and injury to the trees and vines.

“Selective” herbicidal properties of 4–chloro–2–butynyl N–(3–chlorophenyl)carbamate, barban, when applied postemergence for the control of wild oats in cereal grains, have been observed in preliminary trials by a number of workers. Their results suggested that the degree of control was a function of several factors including dosage, volume of diluent, fertility of the soil and the stage of growth of both the weed and crop plants at the time of spraying. Differences in tolerance between grain crops and between varieties within a crop were also indicated.

Recent reviews [Crafts, Currier, Woodford] dealing with the mode of action of phytotoxic chemicals claim the acute toxicity of petroleum oils to plant tissues is due to the destruction of the plasma membrane of the cell. Although considerable evidence supports such a claim, much of it rests on results from the effect of vapors on greenhouse grown plants rather than on the effect of liquid oils on field grown plants. Of the numerous workers who have noted a selective action of oils on different plant species, most of them determined the selectivity by visual observation of injury. Currier and Peoples, Dallyn, and Van Overbeck and Blondeau linked the selective action by experimentation to a differential effect on a cellular level but only the work of Currier and Peoples included direct determinations of cellular vitality. It seemed desirable, therefore, to obtain further information on the relative susceptibility to petroleum oils of field-grown plants.

Witchweed, which parasitizes corn, sorghum, sugarcane, rice, and many other members of the grass and sedge family, was found in 1960 on approximately 167,000 acres of crop land in North Carolina and South Carolina. In 1957, the first year of field studies with witchweed in the United States, there was a general opinion that herbicides would never be feasible for its control. However, Figure 1 shows that witchweed-infested land will respond to methyl bromide, although the cost is prohibitive for field applications.

In the central Great Plains, late summer seedings of alfalfa have often been used in order to avoid the annual weed problem associated with spring seedings. Because moisture conditions are unreliable in the fall, development of techniques to reduce the hazard of annual weed competition in spring seedings offers considerable promise. The authors, in previous reports, indicated that materials that give adequate control of annual weedy grasses and broadleaved weeds are available. These tests were made on plantings of Ranger alfalfa.

The evaluation of herbicidal weed control is often difficult, time-consuming, and non-precise. Neither weed counts, weights, ratings, effects on labor requirements, nor other common methods are wholly satisfactory for general use, although most of these methods are of value for one or more specific purposes.

The selective control of weeds in crops by the use of 3–(3,4–dichlorophenyl)–1,1–dimethylurea (diuron) has had considerable attention the last five years. Some of the problems of applying diuron are how long and at what depths the herbicide remains in the soil after treatment, with different methods and amounts of irrigation.

Bamboos are perennial grasses which exhibit great variation in culm height and diameter and are among the most widespread and useful plants in the tropics. More than fifty bamboo genera have been recognized, and the total number of described species and varieties throughout the world is probably near 1000. In India, this plant is considered the poor man's timber, and it is an irreplaceable basic material for millions of people in the Orient and in South and Central America. Many species are extremely vigorous, however, and become pests when they invade cultivated areas such as coffee farms, lawns, pastures, and sugarcane fields. In some localities, bamboo growth is so rampant as to interfere with the reproduction or development of valuable tree species, and measures must be taken to keep it in check.

The general acceptance of cytochrome oxidase as the terminal link between the various dehydrogenase systems and oxygen in plants was stated in the reviews by Smith and Chance, James, and Hartree.

Madrone (Arbutus menziesii Purch.) and tanoak (Lithocarpus densiflora (H & A) Rehd.) are often considered undesirable along the Pacific Coast. These weed trees are removed to increase forage production; to remove competitors of more valuable timber trees, especially Douglas fir (Pseudotsuga menziesii (Mirb) Franco); or to obtain firewood or charcoal. Tanoak is occasionally cut for tanbark harvest. Control of stump sprouting following cutting would be desirable.

Porter, et al. reported promising results for the use of N–(3,4–dichlorophenyl)methacrylamide (referred to in this paper as (DCMA) as a potential post-emergence herbicide for cotton. These workers found when sprays of DCMA were semi-directed under cotyledons of young cotton, satisfactory weed control could be obtained with little injury to the cotton.

Control of big sagebrush (Artemisia tridentata Nutt.) with fire, chemicals, or mechanical means has long been recognized as an effective method for rangeland improvement. If this sagebrush is killed or weakened by some method of control, excellent stands of grass may be obtained if all conditions are favorable. Bohmont states that as the percentage of sagebrush control increases, the grass and grasslike species also increase.

In a previous study Stadtherr and Widmer reported that several herbicides provided excellent weed control in field plantings of garden chrysanthemums (Chrysanthemum morifolium) The present study was undertaken (a) to compare the best herbicides of the previous study with newer materials, (b) to obtain additional data on herbicides which had been tested for one year only, and (c) to determine the effectiveness of herbicides applied in granular form.

It has been only in comparatively recent years that any appreciable work has been conducted on equipment for the application of chemicals in the soil. Most of the early work was devoted primarily to methods of applying anhydrous ammonia and liquid solutions as fertilizers. In most of this work the principal injection tool consisted of a chisel-type applicator that released the chemical at a single point in the soil. In recent years, investigators have attempted to devise efficient and uniform methods of subsurface distribution. Hedman and Turner reported on a chisel-type applicator equipped with a “fishtail” to give more lateral spread to anhydrous ammonia. Arya and Pickard studied the effect of high pressures and velocities on the application of anhydrous ammonia, which was also single-point injection. Certain problems associated with the application of fungicides and herbicides in the soil have been discussed by Owen and Becker and Costel.

In a previous paper it was reported that there was no difference in the oxidation of ascorbic acid by homogenates from control and N–(3,4–dichlorophenyl)methacrylamide (referred to in this paper as DCMA) treated corn tissues until 3 to 4 days after treatment. At this time, there was a sudden increase in the oxidation of ascorbate by homogenates from treated tissue. The rate of oxidation continued to rise throughout the testing period (0 to 8 days after treatment). Since this appeared to be a significant finding, it was decided the reaction should be pursued further.

The herbicide EPTC (ethyl N,N–di–n–propylthiolcarbamate) offers much promise as a soil-borne toxicant for controlling a variety of common weeds. Not only does it control annuals; it is proving very effective and quite specific in the control of nutsedge. In this role it is unique among the newer materials. In California it has held nutsedge in check during the whole growing season in strawberries, peppers, beans, and other row crops.

(The paper to which this is a supplement appeared in Weeds 3:241–253. The following explanation of the table is repeated from that issue:

“The chemicals are arranged alphabetically according to Chemical Abstracts' nomenclature.

“Density is given at 20°C referred to water at 4°C. Specific gravities are at the indicated temperatures. The melting point is of the commercially used material unless otherwise specified. −H2O. indicates loss of water.

“The pH value is for 5% solutions in water or alcohol unless otherwise indicated.”

It is believed that the abbreviations, tabled in the previous paper, are clear without repetition. Ed.)