Identification and mitigation of acarine pests of hemp (Cannabis sativa)

Hemp plants (Cannabis sativa) are attractive to acarine pests, including Tetranychids, and Eriophyids, like the hemp russet mite (HRM), Aculops cannabicola. Due to their susceptibility to acarine damage, and implemented regulatory restrictions in this crop, the importance of management arises. Our research aims to propose different management strategies focused on acarine pest control, which integrate biorational pesticides and biological control. To detect the most common acarine pests of hemp, surveys were conducted in Homestead, Florida from 2021 until 2023. Tetranychus urticae and T. gloveri were the most prevalent acarine pests. Subsequently, a laboratory screening was conducted to determine the most efficacious products approved for use on hemp against these two spider mite species. The products with the highest efficacy, citric acid and garlic oil, were evaluated under greenhouse conditions, including water as a control. The products were prepared at the maximum label rate and sprayed directly on 30 hemp plants infested six weeks earlier with 30 females of T. urticae of the same age. To evaluate the treatment efficacy, the mite population was scored 24 hours, 7-, and 14-days post treatment application. Finally, Amblyseius swirskii, Amblyseius andersoni, Neoseiulus californicus, and Galendromus occidentalis were evaluated as biocontrol agents against A. cannabicola. Within the first 24 hours post treatment application, garlic oil caused 80% motile mortality, while citric acid caused 58% mortality. Amblyseius swirskii demonstrated the highest predation rate against A. cannabicola. We expect that these findings will benefit the hemp industry and growers to deal with acarine pest infestations.