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.

“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.

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.

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.

(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.)

Competition of downy brome (Bromus tectorum L.) with seeded perennial grasses is an important factor in the lack of success of many seedings on sagebrush conversion areas in the Great Basin. The seriousness of downy brome competition was emphasized by Stewart and Hull. Their work in Idaho indicated repeated failure in seeding of crested wheatgrass (Agropyron cristatum [L.] Gaertn.) on areas where downy brome was not eliminated or reduced. Hull and Pechanec pointed out that many studies indicate that reduction of dense stands of downy brome is essential for the early establishment of seeded species. They also note that in some cases seeding of perennials has been successful without reduction of this weedy annual grass.

The compound, 3–amino–1,2,4–triazole (amitrole), has been used as an herbicide against different weed species with varying degrees of success. In the field, Canada thistle (Cirsium arvense (L.) Scop.) has been found relatively susceptible while field bindweed (Convolvulus arvensis L.) has been found relatively resistant to the action of amitrole. The reason(s) for this difference in sensitivity is not known. Because penetration of amitrole from the surface of the leaf to the interior is the first step in the chain of events leading to a response from a chemical by the treated plant, the nature of this process was examined.

A number of the substituted symmetrical triazines have been shown to possess considerable herbicidal activity. Their high biological effectiveness against a wide spectrum of plants has aroused much interest in their use. While they have been found useful as soil sterilants, they are particularly valuable as selective herbicides on a number of crops. Two of the more promising triazines are simazine (2–chloro–4,6–bis(ethylamino)–s–triazine) and atrazine (2–chloro–4–ethylamino–6–isopropylamino–s–triazine). Both of these compounds have found extensive use in the control of weeds in corn. For this reason, it was of interest to determine the absorption, translocation and metabolism of these compounds by corn plants. The studies of this nature reported here were undertaken using C14 ring-labeled triazines. The labeling of the triazine was accomplished using C14 tagged cyanogen chloride in the synthesis, thus giving a random labeled ring.

Pennisetum clandestinum Hochst. is a vigorous fast growing grass introduced into sub-tropical areas of the United States from tropical Africa in approximately 1920. It has been used for soil erosion control and turf to a limited extent in California. However, in many places it has become a serious weed.

Many of the pathways by which weedkillers, such as 2,4–dichlorophenoxyacetic acid (2,4–D), affect plants are still obscure. Frequently the adverse effect seems to involve an alteration of metabolism, but the exact nature of this is sometimes not clear. Photosynthesis and respiration under different conditions may be either stimulated or inhibited. Other results, in which a decolorization of tissue with increasing amounts of 2,4–D was observed, suggest that the herbicide either interferes with the formation of chlorophyll, or causes increased destruction.

The need for information concerning effects of quality and quantity of light on submerged aquatic plants has been emphasized by the Committee on Aquatic Weed Control at the Southern Weed Conference and by Westman. Factors such as light intensity, water temperature, and depth of water interact with soil fertility to govern the establishment of rooted aquatic vegetation and determine the rate at which it grows.

Drift of spray droplets is a major problem in the application of insecticides and herbicides. Spray drift is the movement of the spray from the place of application to adjacent areas by wind or air currents. Many insecticides and herbicides are effective in minute quantities and even the small amount that drifts can be harmful to crops and livestock. Parathion, 2,4–D, and 2,4,5–T are among those chemicals whose drift is a problem where they are used.

The sodium salt of 2,2–dichloropropionic acid (dalapon) has found a place in chemical weed control practices because of its effectiveness against grasses. The nature of its action is understood only poorly.

Improved methods of weed control through use of herbicides offer important means of reducing production costs and labor requirements in irrigated cotton. The use of pre-emergence herbicides has proved to be an effective tool for annual-weed control in cotton in the humid southeastern cotton region of the United States. Research in Arizona has shown that certain herbicides applied at layby (immediately after the last cultivation) are effective for the control of late-season annual weeds in cotton.

N–(3,4–dichlorophenyl)methacrylamide (hereafter referred to in this paper as DCMA) is a relatively new compound in the field of herbicides. However, several weed control workers (personal communication) have suggested that DCMA may be of value for control of crabgrass (Digitaria spp.), brachiaria (Brachiaria spp.), pigweed (Amaranthus spp.), morning glory (Ipomoea spp.), cocklebur (Xanthium spp.), and goosegrass (Eleusine indica), common weeds found in cotton.

According to Bonner, at least three different oxidase systems may be involved in the final step of the transfer of electrons to oxygen. Each of the terminal oxidases has been shown to occur in many plants and in many relative combinations.

Clagett, Tolbert, and Burris reported an enzyme of widespread occurrence in the green parts of many plants which catalyzed the oxidation of glycolic acid and 1–lactic acid. Zelitch isolated glycolic acid oxidase from spinach leaves and found it to be a flavoprotein with flavin mononucleotide as the prosthetic group. This work was later confirmed by Frigerio and co-workers.

Medusahead, Elymus caput-medusae L., an exotic winter annual grass, was introduced into northeastern Washington and probably adjacent Idaho over 50 years ago. Official records show its presence in southwestern Idaho 15 years ago, but ranchers in this area assert that it was present 25 to 30 years ago. Prior to 1950 it was known to infest a few thousand acres in southwestern Idaho and its distribution from 1945 to 1950 appeared rather static.

The use of pre-emergence herbicides where natural rainfall is low and/or sporadic has not been uniformly successful. In general, the results have been erratic; excellent weed control has been obtained sometimes and a complete lack of weed control at other times. Good weed control is usually obtained when one-half inch or more of rain falls within a few days after application. This result is confirmed in irrigated regions by the fact that overhead irrigation usually gives uniformly good weed control. The standard furrow irrigation usually gives erratic results; however, a furrow irrigation which thoroughly saturates the soil with water to the surface may give good results. Since this type of furrow irrigation is difficult to achieve in practice and the equipment necessary for overhead irrigation is not widely used, the physical incorporation of the herbicides in the top few inches of soil is being widely field tested as a method of application in these areas of low and sporadic rainfall. In general, such incorporation has resulted in a much improved performance under furrow irrigation in the absence of rainfall.

In Arkansas isopropyl N–(3–chlorophenyl)carbamate (CIPC) is recommended for controlling barnyardgrass (Echinochloa crusgalli (L.) Beauv.) in rice. Method and depth of seeding, time of application, and water management after treatment are critical when using CIPC to control barnyardgrass in rice. Rice is very susceptible to CIPC when roots of the seedlings contact the herbicide. A herbicide that is more selective and less sensitive to management and environment is needed to replace CIPC.