Pesticide behaviour in pumice and rockwool growth media; behaviour of metalaxyl and oxamyl in glasshouse cultivation systems

The behaviour of pesticides in substrates is studied to attain adequate low-dosage and low-emission crop protection. The pesticide solution flowed relatively fast through the pumice systems, because less water had to be replaced than in the rock-wool systems. The concentrations in the substrate and in the outflowing solution rose above the concentration supplied because the tomato plant roots took up less pesticide than what corresponds to water uptake. Initially, the transformation rates were low, but they increased as the root systems developed. By pouring the outflowing solution back into the supply tanks, the concentration supplied was maintained high for a long time.