Isopropyl N-phenyl carbamate (IPC) has been used to a limited extent during the past few years as a selective herbicide in the control of weedy grasses and certain broadleaf species. Some investigators have found IPC to be highly effective; others have found IPC to be ineffective. The present investigation and those of Freed (6) indicate that environmental conditions are extremely important in determining the extent of plant response. Shaw and Swanson (8) found that the herbicidal effectiveness of IPC was highly variable under greenhouse conditions.

Sub-tropical climate and rich organic soils in the Florida Everglades produce rank growths of vegetation in ditches and on their banks. This causes some of the most troublesome problems encountered in the field of water control. The regular cleaning of such channels to allow designed flow presents a costly problem to farmers and drainage districts.

The use of Isopropyl N-Phenyl Carbamate (IPC) as a residual pre-emergent herbicide depends on the effective concentration remaining in the soil for a period of time. The effectiveness of such a treatment has been shown to be dependent upon several factors.

Many field studies have indicated the relative tolerance of cotton and other crops to certain chemicals used as pre-emergence weed killers. The possibility does exist, however, that the herbicide may cause injury to the crop when applied prior to emergence of the seedlings. The extent of injury will depend upon a number of factors such as rate of application, depth of seeding, penetration of the chemical into the soil, absorption of the chemical by the young plant and inherent tolerance of the species to a given herbicide. Implicit in each field test is the possibility that, under different conditions of rainfall, temperature and soil type, injury to the seedling crop cannot be ruled out. Some factors can be controlled to provide maximum safety to the germinating crop seeds, but others, such as weather conditions, are largely uncontrollable.

Chemical methods offer a quick means of eliminating crabgrass from lawns and other grassed areas. Sodium arsenite, used since 1935, is the oldest of the selective chemical crabgrass killers. In 1947 phenyl mercuric acetate was reported to be effective as a crabgrass killer in the bentgrass type of turf.

In the years that 2,4–D has been used as a selective herbicide in agricultural areas, an increasing number of reports of its injury to crops has been published. As a result of extensive investigations, lists of susceptible and resistant crops have appeared. Some of the extremely susceptible crops include cotton, sugar beets, alfalfa, tomatoes, peas, beans, cabbage, broccoli, lettuce, grapes, and many others. In response to numerous reports of 2,4–D injury to various small grains, we now consider these plants as being relatively susceptible to 2,4–D at certain stages of development also. The morphological injuries reported may be just as severe as in the case of some of the above-mentioned plants.

Intensive research in pastures and forage crops has stimulated an increased interest in grassland farming in the southern states. A great deal of emphasis has been given to the various phases of establishment and maintenance of permanent pastures. However, very little work has been reported on the possible use of chemicals for controlling weeds in grass-legume mixtures.

Within the past few years the use of chemicals as herbicides has increased so rapidly that today in the United States alone millions of acres are being treated in the fight to control weeds. In addition to determining the effect of these chemicals on the plants involved (both desirable ones as well as weeds), it is most important to find out how the compounds affect the soil microflora. This assemblage of microscopic organisms plays a most vital role in the balance of nature, and, if the herbicide to be employed has as great an effect on the soil population as it does on the higher plants, its use might be impractical due to the resultant imbalance.

Since CMU (3-(para-chlorophenyl)-1,1-dimethylurea) has been shown to be a potent herbicide which persists in the soil for long periods of time (1, 2, 3) it was tested in the following experiments to control nutgrass (Cyperus rotundus L.).

A high quality cordage fiber can be obtained from certain species of sansevieria (3, 5, 8, 10). Laboratory and small scale manufacturing tests indicate that this fiber is a suitable substitute for abaca, a fiber which is critical for defense purposes. (1,9). Weed competition has been a major problem in the culture of sansevieria for fiber because the plant has a slow rate of growth and a long period of time is required to develop a stand.

It has been noted frequently that salts of 2,4–dichlorophenoxyacetic acid, such as sodium or triethanolamine salt, are effective as herbicides in regions of moderate rainfall, while in arid regions they are sometimes relatively ineffective. Usually, and particularly under arid conditions, the aliphatic esters of 2,4–D have been more effective as herbicides than the salt forms.

Renewed interest in volatility of hormone-like compounds has occurred since government restrictions were placed on the sale of certain esters used for herbicidal purposes. After crop plants neighboring on fields sprayed with volatile herbicides were injured, attempts were made to find low volatile esters which could be used with greater safety. This was done by making long chain esters containing five or more carbon atoms. Since many of these are now being made, the problem is to find satisfactory test methods for determining the relative volatility as compared with known compounds and standard formulations.

The discovery of the herbicidal properties of isopropyl N-phenylcarbamate (IPC) and isopropyl N-(3-chlorophenyl)carbamate (CIPC) and other organic chemicals has created an impetus in the development of new herbicides. Since the discovery of 2,4-dichlorophenoxyacetic acid (2,4-D), considerable effort has been devoted to the development of herbicides that are as effective and selective for the control of annual grasses as is 2,4-D for the control of many broad-leaved weeds.

Sodium 2,4–dichlorophenoxyethyl sulfate (hereafter designated as SES) has been widely tested for herbicidal use in pre- and post-emergence applications on seeded and vegetatively propagated crops. Several investigators have found this chemical to be particularly valuable for control of annual weeds in strawberries. Their reports indicate satisfactory weed control, but for the most part contain no critical evaluation of the effect of the chemical on the strawberry plants. Field tests conducted on crops other than strawberries have indicated some crop responses which may be characteristic of the general effects to be expected from application of SES to crop plants. More basic studies have shown no hormone response from application of SES to tomato foliage. In fact, the chemical per se was found to be herbicidally inactive, undergoing some change in the soil to attain its active form. The change from inactive to active form was found to occur in nonsterile soils over a range of pH from 3 to 7, and in sterile soils from pH 3 to 4. This change was postulated to be an acid hydrolysis of the ethyl sulfate form of the chemical to an active form, either in an acid soil or as a result of acid secretions of bacteria and fungi. Further research has indicated that SES is hydrolyzed to sodium 2,4–dichlorophenoxy ethanol and sodium bisulfite and that further reaction in the soil may lead to 2,4–dichlorophenoxy-acetic acid. The ethanol has been shown to be highly toxic to germinating seeds, but only 1/100 as toxic as 2,4–D when applied to tomato foliage.

It has been reported by Carroll (1,2) that light activated riboflavin will counteract 2,4-D inhibition, presumably due to an inactivation or destruction of the 2,4-D molecule. Hansen and Buchholtz (7) found that light activated riboflavin would inactivate the 2,4-D molecule in vitro and it appeared that 2,4-dichlorophenol was one of the decomposition products. Galston (3, 4, 5) has shown that riboflavin may act as a photo-receptor and a hydrogen carrier in the oxidation of indol-3-acetic acid, the reduced riboflavin being re-oxidized by the air. It would appear, therefore, that riboflavin may play an important role in the breakdown of growth substances in the plant.

Certain members of the phenyl carbamate series and some salts of trichloroacetic acid have been known for several years to possess strong herbicidal properties, particularly toward monocotyledonous plants. This action has been described by Ivens and Blackman (4), McCall and Zahnley (5), Freed and Bierman (2), and others. Inconsistent results obtained in the usage of these chemicals have discouraged many workers from accepting them as useful weed control tools. Recently, Freed (3) analyzed several factors influencing the success or failure of IPC (isopropyl–n–phenyl carbamate). Among these are biochemical specificity, decomposition by soil microorganisms, moisture requirements, and stage of plant development. It has also been demonstrated by Anderson et al (1) that rapid evaporation of carbamates may be a critical factor at temperatures above 75 °F.