Evaluation of biorational pesticides against acarine pests of hemp (Cannabis sativa): A greenhouse approach and production of mite-free cuttings

Industrial hemp (Cannabis sativa L.) is a crop with a delta-9 tetrahydrocannabinol (THC)
concentration of less than 0.3 % on a dry weight basis, which distinguish it from Marijuana plants.
Hemp plants are attractive to insect and mite pests. Common acarine pests include spider mites
(Tetranychus urticae, T. gloveri), broad mites (Polyphagotarsonemus latus) and russet mites
(Aculops cannabicola). Despite the high number of common pests that affect hemp, in Florida
chemical control is restricted and only approved by the Florida Department of Agriculture and
Consumer Services – Division of Plant Industry (FDACS-DPI) products can be applied. Our
research aims to evaluate FDACS-DPI approved biorational pesticides to control the most
common acarine pests on hemp. Single active ingredient products were selected and included citric
acid, rosemary, thyme, sesame, and garlic oil. A mineral oil was also included as a positive control
and water as a negative control. The products were prepared at the maximum label rate and sprayed
either on leaf discs (1 cm diameter) as indirect contact or directly on the mites as a direct contact.
Mite mortality was evaluated, where live and dead mites were scored. The most efficacious
products were Garlic oil, citric acid, and thyme oil to control all the species evaluated. Garlic oil
and citric acid were evaluated for their potential to produce mite free propagative material. Garlic
oil, citric acid and thyme oil will be further tested against T. urticae and T. gloveri, under
greenhouse conditions.