The residual effects of four selective herbicides upon the growth and development of winter cover crops

Since about 1955, soil applied herbicides have been extensively used in horticultural and agronomic crops for weed control. After the period of desired control, the herbicides must be inactivated or decomposed before susceptible crops can be grown. Herbicidal activity depends upon numerous soil properties, the kind of herbicide, the plant sensitivity to the herbicide, and the climatic conditions under which the herbicide is applied. It is apparent that the herbicide soil plant weather interaction is complex and considerable research is needed before the environmental and physiological problems of herbicide utilization are solved.

N,N-dimethyl-a,a-diphenylacetamide (diphenamid), ethyl N,Ndi- n-propyIthiolcarbamate (EPTC), and N,N-di-n-propy1-2,S-dinitro-4-trifluoromethylanaline (trifluralin) have been widely accepted as soil applied herbicides. The wide use of these in vegetable crops creates a need for an evaluation of their residual effects on subsequent cover crops commonly grown following vegetables.

The objectives of this investigation were threefold. The first was to determine the residual effects of the above three herbicides and Amchem D-263, a new experimental herbicide, upon the growth and development of fall seeded rye, oats, and crimson clover. The second was to determine whether the herbicides were present in various layers of the top nine inches of soil at the time of fall seeding in concentrations great enough to impair cover crop growth. The last was to determine the time necessary for complete loss of herbicidal toxicity to the above crops.