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.

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.

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.).

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.