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The value of ecollogically acceptable insecticide combinations for Colorado Potato Beetle control

Colorado potato beetle is the most notorious and problematic insect defoliator pest of potato and threatens crops in nearly all major potato growing regions. Colorado potato beetle is well known for its ability to develop resistance to chemical insecticides and therefore new and novel treatment methods must be developed and explored. Integrated Pest Management provides the soundest approach to controlling Colorado potato beetle and slowing and preventing resistance development. This work investigated the use of ecologically acceptable insecticide treatments: azadirachtin, spinosad and spinetoram. Reduced dosing and combinational treatments were used to determine if satisfactory efficacy could be achieved while also improving economic results. In 2019 a field trial was conducted with ten treatments and one control. The treatments included the three active ingredients at full and reduced dosing as well as the combination of azadirachtin with spinosad and azadirachtin with spinetoram, both combinations were also carried out at reduced dosing. Efficacy was calculated using the Abbott formula. The results showed that a 50% reduced dose of azadirachtin provided unsatisfactory efficacy results while the full dose provided low to moderate efficacy (47%-84%). Both a 100% full dose and 50% reduced dose of both spinosad and spinetoram provided satisfactory efficacy results (83%-99%), with residual activity of 10-14 days. The 10% reduced dose of both spinosad and spinetoram provided low efficacy results, with the exception of spinosad around day 14-21, where the efficacy improved (75-80%). The combination of a 50% dose of azadirachtin with either a 10% dose of spinosad or a 10% dose of spinetoram only provided moderate efficacy at best, with spinosad (58%-81%) outperforming spinetoram (41%-74%). Both combinational treatments showed the peak efficacy around day 5. Based on the advantages that these treatments offer compared to synthetic chemical insecticides, further work is recommended to determine if these combinational treatments can offer satisfactory efficacy results. The use of 50% reduced dosing of both spinosad and spinetoram is recommended as a treatment method which provides satisfactory efficacy, improved economic results as well positive ecological fate.

biological control ; Leptinotarsa decemlineata Say ; Colorado potato beetle, Solanum tuberosum, insecticide resistance management, reduced-risk insecticides ; integrated pest management (IPM)

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