Sensitivity of Grasses and Some Crop Plants to Isopropyl-N-Phenyl Carbamate

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Abstract
Seeds of grasses and dicotyledonous plants were sown in fertile potting soil to which iso-propyl-n-phenyl carbamate (IPC) was added. In some expts. the carbamate was mixed with quartz sand, and this mixture was added to soil and the seeds planted. In other expts. the mixture was spread evenly on the surface of the soil after it was plotted and the seeds planted. The amt. of sand used was 10 gm./lb. of soil. The IPC affected the growth of grass seedlings in varying degrees. When applied to the soil surface at a rate equiv. to 2 lbs./acre, IPC prevented the emergence of quack grass seedlings, while 91% of the seeds-in untreated soil emerged and grew well. When the same amt. of IPC was worked into the upper 1 inch of soil, 18% of the seedlings emerged and grew well. IPC applied at a rate equiv. to 2 lbs./acre and cultivated to a depth of 4 inches was even less effective in preventing emergence. Emergence of blue grass seedlings was greatly reduced in soil that contained only 3.4 mg. of IPC/lb., while the emergence percentage for crab grass increased with addition of IPC to the soil. The later growth of the latter was greatly inhibited. The effect of IPC varied from complete inhibition in the case of quack grass, fescue, and others to stimulation of growth during the early stages of development of Bermuda grass and crab grass. Applied at 30-60 lbs./acre, the effect on the growth of less sensitive spp. was prolonged and these plants were stunted and failed to produce seeds. When applied at 50-100 lbs./acre to potted soil in which crab grass was established and had developed leaves about the surface, the plants died 2 wks. after treatment. Seeds of sugar beets, table beets, carrots, radishes, onions, and spinach were planted with measured amts. of quack grass seeds in soil to which diff. amts. of IPC were added. When applied evenly to the surface at the rate of 2 lbs./acre, IPC completely prevented emergence of quack grass but only temporarily checked sugar beet seedlings. The emergence for onions was not reduced by IPC at rates of 2, 4, or 8 lbs./acre. The growth of radishes was slightly less in soil treated at the rate of 2 lbs./-acre than in untreated soil. The growth of spinach and table beets was not affected by IPC at the latter rate to soil in which the seeds were germinated and the plants grown for 6 wks. IPC was inactivated in moist fertile soil. Quack grass failed to survive, in testing for inactivation of IPC, when the seeds were planted in soil to which 40.8 mg./lb. of soil was freshly added. Subsequently the soil was kept moist for 2 months and reseeded. There was germination of 84% of the seeds and the plants grew vigorously, showing that the IPC was inactivated. The results show that IPC may be useful in reducing the population of some weedy grasses, such as quack grass.
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