Chlorpyrifos-methyl as a Protectant of Farmers Stock Peanuts¹

Runner variety farmers stock peanuts were treated with either distilled water, 52 ppm malathion. or chlorpyrifosmethyl (CM) applied at 10, 15, 20 and 25 ppm, held in a metal shed and artificially infested with insect pest species commonly found in stored peanuts. Peanuts were sampled at 2, 4, 6, 9 and 12 months post-treatment. After 6 months ca 22% of loose-shelled kernels (LSK) in malathion-treated peanuts were damaged by insects; after 9 and 12 months damage increased to 36 and 49%. In contrast, LSK damage in peanuts treated with CM exceeded 6% after 9 and 12 months only in the 10 ppm treatment. Damage to kernels from cracked pods in malathion-treated peanuts was 6.9 and 11.2% after 9 and 12 months, respectively, but damaged cracked pod kernels exceeded 2% only in the 10 ppm CM treatment at 12 months. Degradation of CM residues occurred more slowly than malathion residues during the final 6 months of the test.