Assessment of the grain protectants chlorpyrifos‐methyl plus bioresmethrin, fenitrothion plus (1<i>R</i>)‐phenothrin, methacrifos and pirimiphos‐methyl plus carbaryl under practical conditions in Australia

Abstract

Abstract Methacrifos (22.5 g t −1 ) and the three protectant combinations chlorpyrifos‐methyl (10 g t −1 ) plus bioresmethrin (1 g t −1 ), fenitrothion (12 g t −1 ) plus (1R)‐phenothrin (2 g t −1 ) and pirimiphos‐methyl (4 g t −1 ) plus carbaryl (8 g t −1 ) were each applied to grain that was stored in at least 15 silos. Grain temperature and levels of protectant were regularly monitored, and samples from 12 storages using each treatment were taken for laboratory assays against Rhyzopertha dominica and Tribolium castaneum. Grain condition did not deteriorate during storage. Grain remained free of insects in 60 of the 63 storages treated; partial failure in the other 3 storages was attributed to low or irregular levels of protectant. The mean and range of residue values of all protectants were recorded as a function of time and the mean observed values corresponded to predicted values. In laboratory bioassay, the order of effectiveness against T. castaneum was methacrifos &gt; chlorpyrifos‐methyl plus bioresmethrin &gt; fenitrothion plus (1R)‐phenothrin = pirimiphos‐methyl plus carbaryl. The order of effectiveness against R. dominica was carbaryl plus pirimiphos‐methyl = (1R)‐phenothrin plus fenitrothion &gt; methacrifos &gt; bioresmethrin plus chlorpyrifos‐methyl.