Insecticides for the protection of stored potatoes

Abstract

In four tests in Queensland in 1966-67, six insecticides were evaluated in dusts against Phthorimaea operculella (Zell.) (terrella (Wlk.)) infesting stored potatoes. In tests with dry potatoes, the percentage infestation 83-85 days after treatment with 0.5% endrin, 1.0% rotenone or malathion (maldison), 2.0% DDT, a mixture of 0.25% pyrethrins with 2.0% piperonyl butoxide, and 2.0% trichlorphon averaged 11.9, 14.2, 14.4, 15.9, 16.4 and 65.6, respectively, in potatoes that were not initially infested artificially, as compared with 70.8% for no treatment. When infested potatoes were deliberately incorporated with those treated, the corresponding percentages were 32.5, 20.2, 29.2, 31.6, 31.7 and 98.2, as compared with 98.9%. In further tests, intended to simulate commercial practice in Queensland, the treatments were applied to freshly dug tubers carrying moist soil (trichlorphon being omitted) and the percentage infestations for no artificial infestation and (in brackets) artificial infestation averaged 12.9 (15.7), 8.4 (8.3), 17.3 (16.2), 7.2 (9.7) and 19.2 (15.8), respectively, as compared with 88.0 (99.3). Endrin is considered too toxic for use on stored potatoes; when malathion and pyrethrins were used, rather more potatoes rotted than with DDT or rotenone, so that rotenone (as derris dust) is recommended for commercial use. ADDITIONAL ABSTRACT: 6 insecticides were tested in 4 trials for the protection of stored potatoes against infestation by the potato moth Phthorimaea terrella. Derris dust containing 1% rotenone was the most satisfactory and performed well with freshly-dug tubers carrying moist soil as well as with dry tubers, including conditions of increased pest populations. DDT 2% dust and maldison 1% dust gave comparable results with dry tubers, but DDT was superior to maldison when applied to freshly-dug tubers. Endrin 0.5% dust was effective in limiting infestation but the toxic nature of this insecticide precludes its use for potato storage. Trichlorphon was inefffective. Rotting of tubers was greatest when maldison was used.