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Multiple Cottonseed Treatments: Effect of Sequence of Application of Pesticides on Germination, Seedling Growth, and Survival¹

This study evaluates the effect of the sequence of application of pesticides used as seed treatments on germination, seedling growth, and field survival of cotton (Gossypium hirsutum L.). In separate tests three protectant fungicides, 2-(thiocyanomethylthio)benzothiazole (Busan 72), pentachloronitrobenzene + 5-ethoxy-3-trichloromethyl- l,2,4-thiadiazole (Terracoat L21), or bis(dimethylthiocarbamyl) disulfide (thiram) were used with the systematic fungicide l,4-dichloro-2,5-dimethoxybenzene (chloroneb) and the systemic insecticide 0,0-diethyl S [2-(ethylthio)ethyl] phosphorodithioate (disulfoton), and were applied in all feasible combinations of the various pesticides. Evaluations included germination tests at standard conditions, at constant 20 C, and a constant 30 C. Dry weight transfer (DWT) determinations were made at 20 and 30 C, and seedling survival in the field at Stoneville, Miss. 42 days after planting.

In all three studies the results indicated that the sequence of pesticide treatment affected subsequent performance of cottonseed. In the case of Terracoat L21, only seedling survival in the field was not significantly affected by the sequence of pesticide application. ‘Traditional’ sequence of application — protectant fungicide followed by the systemic fungicide and then by the systemic insecticide — was the best sequence with these pesticides. When Busan 72 was used, alternative sequences proved to be more effective. When thiram was used, application of disulfoton first, irrespective of the application sequence of the other pesticides, reduced seedling survival and germination values at 20 C. Our results indicate that any change in pesticide usage, where multiple pesticides are used for seed treatment, may require a change in the sequence of pesticide application to obtain optimum results. In some instances, germination values may be affected to the point that treated seed would be rejected for certification and possible sale because of substandard germination, whereas untreated seed would have been acceptable.

Key Words: Fungicides • Thiram • PCNB • Chloroneb • Systemic insecticides • Disulfoton • Chemical interactions • Gossypium hirsutum L

² Research Plant Pathologist and Research Assistant, ARS, USDA, Plant Industry Station, Beltsville, Md. 20705.

Received for publication May 19, 1972.