Abstract: In an effort to develop easily available, affordable and biodegradable reduced-risk insecticides as alternatives to conventional synthetic post-harvest protectants against storage weevils, powders of Chenopodium ambrosioides were tested singly and in combination with the often used wood ash under ambient laboratory conditions on Sitophilus zeamais infested maize. This is a major impediment to sustained food security in Africa and other developing countries. The powders were mixed at varied doses of C. ambrosioides (0.5-2 g) powder per 50 g of maize grains; there was also a positive control of Actellic® powder and an untreated negative control. Grains treated with 2 g of C. ambrosioides powder caused 100% adult weevil mortality within 3 days after infestation. At 2 g, C. ambrosioides powders were as good as Actellic® powder on adult weevil mortality, protection of grains against damage and reduction of number of weevil progeny produced within 1-2 months of storage. The grain weight loss decreased with increased concentration of plant powder used but increased with longer duration of storage. The persistency effects of C. ambrosioides powder decreased over time till the powder lost its potency on adults beyond three weeks of grain storage. A proportional combination of 50:50% of C. ambrosioides powder and wood ash killed S. zeamais adults at a faster rate than either powder singly. The results indicate that the use of mixtures of C. ambrosioides powder and wood ash by small scale farmers is potentially a cost-effective and sustainable alternative or supplement to synthetic chemical insecticides for large-scale maize storage.