LEACHING OF PESTICIDES THROUGH CONTAINER PEAT MEDIUM IN FOREST SEEDLING PRODUCTION

Most of the pesticides used in container production are sprayed on the very densely growing forest seedlings. Therefore pesticide load into the ground is composed of leachates from the growing medium in the containers and the amounts sprayed outside seedlings. Leaching of propiconazole (Tilt 250 EC^®) and chlorothalonil (Bravo 500^®) through light Sphagnum peat medium in containers was monitored in nursery production of Scots pine (Pinus sylvestris L.) seedlings. The data concerning the leaching of the fungicide triadimefon (Bayleton 25^®) and the insecticides cypermethrin (Ripcord ^®) and alpha-cypermethrin (Fastac^®) was collected from silver birch (Betula pendula Roth) production. In addition, leaching of these pesticides was studied in experiments with simulated rainfall. The seedling canopy and light Sphagnum peat medium adsorbed pesticides effectively. During the growing period, less than 4% of the applied chlorothalonil, triadimefon, cypermethrin and alpha-cypermethrin leached from the container trays. Propiconazole was an exception; almost 30% of applied amounts leached. Fluctuations were typical for the concentrations of the pesticides in leachates; the concentrations were usually highest after application and decreased before new applications. In experimental studies the concentrations were highest on the first day after application and then decreased rapidly during the following ten days. Greater proportion of the applied pesticide amounts leached under experimental conditions than did in field studies. In conclusion, irrigation and rain removed pesticides from seedlings and leached them from containers, especially during the first three days after pesticide application, therefore it is important to plan the irrigation schedules so that the percolation of water from containers is as small as possible during these days.