Malathion on milling fractions of three varieties of rough rice: duration of protection and residue degradation.

Abstract

Malathion deposits of about 11, 17, and 20 ppm protected rough rice for 6 to 12 months under Gulf Coast environmental conditions. Protection lasted slightly longer in bin tests than in jar tests. Residues on rough rice greater than 8, 4, and 2 ppm were required to control confused flour beetles, Tribolium confusum Jacquelin duVal; lesser grain borers, Rhyzopertha dominica (F.); and rice weevils, Sitophilus oryzae (L.), respectively. Initial deposits on rough rice were 20 ppm; deposits decreased to levels below 8 ppm within 3 months. Initial deposits on hulls were 80 ppm; deposits did not fall below 8 ppm for 7 to 11 months. Residues on bran and milled rice increased for 3 months and then declined. Residues on bran reached a maximum of 30 ppm but fell below 8 ppm in 6 to 10 months; on milled rice. maximum residue was 0.32 ppm. Varieties of bran and milled rice retained malathion in the following order: ‘Belle Patna’ > ‘Nato’ > ‘Dawn.’ This ranking apparently was dependent upon the relative surface area and the thickness of the covering hull on kernels of each variety.