Granulated systemic insecticides applied into the soil are more selective than conventional spray or dust applications as only certain phytophagous species are exposed. Soil moisture and water solubility of the chemicals were studied as to effect upon absorption and translocation in insecticidal quantities. The materials of very low water-solubility studied (phorate and Di-Syston®(O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate )) took as much as two or more weeks longer to attain aphid mortalities obtained in a few days with moderately water-soluble dimethoate (O,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorodithioate) and Di-Syston sulfoxide (O,O-diethyl S-2- (ethylsulfinyl)ethyl phosphorodithioate) and water miscible OS-1836 (diethyl 2-chlorovinyl phosphate). Furrow irrigation increased the speed of absorption markedly by carrying toxicant as the moisture moves through the soil towards the roots if granules are banded between the irrigation furrow and the plant row. From these data it is theorized that compounds of extremely low water solubility move too slowly into the root zone to attain optimum insecticidal value from soil applications; conversely, readily soluble or water miscible compounds might lose effectiveness more quickly by widespread movement in the soil and thus become lost to the root zone.
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Reynolds et al. (1962) studied this question.
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