The Use of Systemic Insecticides on Potted Chrysanthemums in the Greenhouse

Abstract

Four series of experiments to control the two-spotted spider unite, Tetranychus telarius (L.), with systemic insecticides applied only on the soil show significant results. Test plants were potted chrysanthemums grown in a greenhouse under usual commercial conditions. Demeton at the rate of 32 milliliters of the commercial preparation in 32 gallons of water per 100 square feet of soil surface protected the plants from mites for approximately 5 weeks. Ten per cent phorate granules at the rate of 2.50 grams per 100 square feet required 1 week to become effective, but usually protected the plants from mites until blooms appeared. It was the most effective chemical tested in control of flower thrips, Frankliniella tritici (Fitch). Phosphamidon and Zectran® (4-dimethylarnino-3. 5-xylyl methylcarbamate) remained effective in control of mites for a shorter period of time than phorate, and a stronger dosage of granules of Di-Syston® ( O,O -diethyl S -[2-(ethy]thio)ethyl] phosphorodithioate) was required to control mites adequately. Dimethoate burned the plants severely at all concentrations used.