Influence of humidity and rain on uptake and metabolism of 14C-azinphos-methyl in bean plants.

In several experiments the influence of relative humidity and rain on uptake and metabolism of carbonyl-14C-azinphos-methyl was examined in bean plants under the following environmental conditions: Growth room with 35/80%, 65/85% and 95/95% (day/night) relative humidity and open field with and without rain. Increasing relative humidity had an enhancing effect on the rate of uptake and metabolism. A higher portion of water-soluble compounds was found in the bean tissue, although the azinphos-methyl itself is relatively non-polar. Low relative humidity and possible dry periods in summer will reduce the uptake and will leave the azinphos-methyl relatively persistent on the leaf surface. Rain or spray irrigation easily removed azinphos-methyl from the leaves. The rate of this removal seemed to depend on the intensity and time of rainfall after application. However, repeated wettings by rain may simultaneously stimulate uptake and metabolism of azinphos-methyl by the leaves.