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Allium leafminer, Phytomyza gymnostoma Loew (Diptera: Agromyzidae), is an invasive pest of allium crops in North America. Spinosyn insecticides, spinetoram and spinosad, have been effective choices for managing P. gymnostoma infestations in allium crops, but their use should be optimized for economical and resistance management purposes. In New York from 2018 through 2020, performance of each spinosyn insecticide was evaluated by making two applications spaced either 1 or 2 wk apart beginning at various intervals after P. gymnostoma was first detected in the field; a weekly spray program also was included. Results indicated that weekly applications of each spinosyn insecticide provided ≥98% reduction of P. gymnostoma densities in scallions and leeks relative to the untreated control. Spinetoram applied twice, regardless of initial timing and duration between sprays, provided an acceptable level of P. gynostoma control (71 to 98% reduction in densities relative to the untreated control). Spinosad also was effective when applied twice (85 to 95% reduction in densities relative to the untreated control), but not when sprays were made consecutively beginning when P. gymnostoma was first detected and not when the P. gymnostoma infestation was extremely high (i.e., 38 insects per plant in the untreated control). Management of P. gymnostoma with spinosyns can be successful with only two applications, but control tended to be best when first applied 2 to 3 wk after initial detection. Optimizing applications of spinetoram and spinosad will save growers time, reduce insecticide costs, and mitigate resistance development without significantly increasing the risk of yield reduction., (© The Author(s) 2022. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Allium leafminer, Phytomyza gymnostoma Loew, is the newest invasive pest of allium crops in North America. Larvae initially feed in the upper canopy before mining toward the base of the plant to pupate. Crop loss occurs when larvae destroy vascular tissue, facilitating infection by bacterial and fungal pathogens that cause rot. Contamination also occurs when larvae and pupae are present at harvest. In response to this invasion, efficacy of 14 insecticide active ingredients applied via foliar sprays, transplant treatments, and drip chemigation was evaluated for managing P. gymnostoma. Multiple field studies were conducted in onions, leeks, and scallions in Pennsylvania and New York, United States in 2018 and 2019. The highest and most consistent levels of P. gymnostoma control occurred using foliar applications of dinotefuran, cyantraniliprole and spinetoram (84-89% reduction in damage; 95% reduction in P. gymnostoma densities). Despite the success of dinotefuran and cyantraniliprole applied as foliar sprays, neither was effective in controlling P. gymnostoma when administered via drip chemigation. Other foliar-applied insecticides that significantly reduced densities of P. gymnostoma in one or two experiments included abamectin, acetamiprid, cyromazine, imidacloprid, lambda-cyhalothrin, methomyl, and spinosad. Active ingredients that never controlled P. gymnostoma included azadirachtin, kaolin clay, pyrethrin, and spirotetramat. Spinosad applied to bare-root and plug-tray transplants immediately before transplanting reduced P. gymnostoma damage in the field by >90%. Implications of using these insecticides and application strategies are discussed within the context of developing a sustainable IPM program., (© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)