Insecticide and Fungicide Residues Following Foliar Application to Cotton and Soybean

The control of target pests and impact on non-target arthropods, including pollinators, is affected by the persistence of pesticides on plants following an application. A study was conducted in Tennessee to investigate the levels of pesticide residues on cotton, Gossypium hirsutum L., and soybean, Glycine max (L.), following a foliar application made during early flowering. Residues of four classes of insecticides and three classes of fungicides were assessed at 1, 24, 72, 144, and 216 h after application on cotton leaves, anthers of cotton flowers, and soybean flowers. Active ingredients included acephate, imidacloprid, lambda-cyhalothrin, chlorantraniliprole, fluxapyroxad, pyraclostrobin, and propiconazole. Initial pesticide residues on cotton leaves were many times greater than those on cotton anthers or soybean flowers. With the exception of chlorantraniliprole on cotton leaves, fungicide residues persisted longer than insecticides. Also, pesticide residues on soybean flowers degraded more slowly than those on cotton leaves or anthers. For cotton leaves, insecticide residues decreased sharply within 24 h after application except for chlorantraniliprole. All pesticide residues on cotton anthers were dramatically lower 24 h after application, indicating little systemic movement to pollen. By 216 h after application, and considerably sooner in most scenarios, pesticide residues on cotton and soybean had diminished by 90% or more. The implications of these results on pest management and pollinator safety are discussed.