Twospotted Spider Mite Control on Marigold Plants in the Greenhouse, 1992

Thirty-six ‘Yellow Boy’ marigold plants at a Michigan State University research greenhouse were used for this experiment. The plants were grown to a height of 10 inches in 6-inch diameter clay pots. They were watered with a drip irrigation system three times per week. On 8 Apr the plants were infested with twospotted spider mites raised from a bean culture in the laboratory by placing infested leaves on the test plants. The precounts were made on 29 Apr by collecting 4 leaves from each plant and counting the number of mites on the underside of each leaf with a dissecting microscope. Plants were sprayed to runoff on 29 Apr with a R&D C02 sprayer with an 80° #3 nozzle at 50 psi. Postcounts were made on 5, 12, and 26 May in the same manner as the precounts.