Toxicity of maleic hydrazide in California soils

does not appear. First page follows. Introduction The studies presented in this paper are an attempt to answer certain questions involved in the relations between maleic hydrazide (1,2 dihydropyridazine—3,6 dione) and different soils. These questions grew out of the fact that maleic hydrazide may acquire importance as a selective herbicide if proved successful in field tests and that spray residues left on the soil may affect subsequent crops. The studies may also indicate the value of maleic hydrazide as a temporary selective soil sterilant or as a preëmergence spray. Maleic hydrazide when pure is a white crystalline solid, soluble 0.4 per cent in water at room temperature, and slightly acid in reaction. It has been prepared in various formulations, among which is the water-soluble diethanolamine salt (Schoene and Hoffman, 1949).4 Research already conducted on this chemical furnished some data on its effect on plant growth. Experiments by (Schoene and Hoffman (1949)) indicated that maleic hydrazide had temporary but strong inhibiting effects on plant growth. (Currier and Crafts (1950)) in screening experiments, showed that 0.2 per cent spray killed two-weeks-old barley, yet had no apparent effect on five-weeks-old cotton. They reported that the age of the plant was critical; for example, cotton in the cotyledon stage was severely inhibited and older grasses were less susceptible than young grasses. In general, grasses were found to be more susceptible to maleic hydrazide than broad-leaved plants; and broad-leaved plants were found to be more tolerant the more mature they were at spraying time (Crafts, Currier, and Day, 1950). Subsequent investigations by (Crafts, Currier, and Day (1950)) indicated that maleic hydrazide was a growth regulator of the hormone type and could be translocated by plants.