Effects of Various Soil Types and Methods of Application upon Uptake of Three Systemic Insecticides by Cotton Plants in the Greenhouse1

Abstract

Plant uptake, persistence, and insecticidal efficiency of three systemic insecticides (phorate, demeton, and dimethoate) were studied on cotton plants in the greenhouse. Materials were applied as seed treatments and as granulated formulations (on attaclay and vermiculite carriers) at time of planting and to established plants. Pour soil types were included: fine sandy loam (Moreno, pH 7.1); loamy fine sand (Indio, pH 9.1); clay loam (Imperial Valley, pH 8.1); and silty loam (San Marcos, pH 6). All seed treatments retarded germination, especially in the lighter soils; soil treatments at time of planting produced the same trend but less severely. Phytotoxicity was most pronounced with seed treatments; the effects from insecticides on vermiculite granules applied at planting were more severe than from those on clay granules. Plant injury was more severe in lighter soils. The injury caused by dimethoate seed treatment was the most severe, with phorate- and demeton-caused injury following in order of decreasing intensity. Granulated formulations applied to the soil on established plants gave typical systemic burn on the leaf margins that was most severe on dimethoatetreated plants. Bioassay with spider mites, Tetranychus cinnabarinus (Boisd.), revealed highest initial concentrations of toxicants in the plants grown from treated seed. The light soils allowed the fastest uptake of toxicants and the highest levels of toxicant concentration within the plants. Vermiculite granules released toxicants more rapidly than clay granules but residual activity did not persist as long. Granulated dimethoate reached lethal concentrations in the plant most rapidly but lost its effect most quickly; phorate showed the greatest persistence. Soil pH did not prove to be a major factor in toxicant uptake, but soil texture was important, the lighter, sandy soils allowing materials to be absorbed by plant roots more rapidly. Leaching experiments demonstrated the faster movement of the systemic insecticides in sandy soils. Similar experiments demonstrated a quicker release of toxicants from vermiculite than from clay granules.