Factors that influence chemical control of scale insects

Armored (Diaspididae) and soft scales (Coccidae) are economically important groups of scale insects and their management is commonly generalized on pesticide label directions. However, we have found these two groups respond differently to several factors in successful integrated pest management (IPM) programs. Our studies showed that armored scales are susceptible to a wide range of different active ingredients and classes including reduced-risk and broad-spectrum products, while soft-scales are susceptible to fewer products. Because reduced-risk and broad-spectrum products have similar efficacy on armored scales, products with the lowest negative effect on natural enemies should be prioritized in armored scale IPM programs. For example, horticultural oil, pyriproxyfen, spiromesifen and spirotetramat are reduced risk insecticides that have shown similar control compared to broad-spectrum insecticides with less impact on natural enemies. Similarly, foliar and soil applications of systemic insecticides manage armored scales equally well, but soil applications of systemic insecticides have less negative effects on natural enemies. Unlike armored scales, we found that bifenthrin and pyriproxyfen are the only insecticides tested that consistently killed soft scales. This limits the insecticide options and rotations to manage soft scales. Also, soft scales can excrete non-metabolized insecticides through honeydew. This tainted honeydew may negatively affect beneficial insects, such as predators, parasitoids, and pollinators, that feed on it. In conclusion, it is critical to avoid generalizations because soft scales have the potential to impact beneficial insects through tainted honeydew and they tend to be more tolerant to a wider range of different active ingredients compared to armored scales.