DISSIPATION OF AEROSOLS FROM GREENHOUSE AIR AFTER APPLICATION OF PESTICIDES USING A LOW-VOLUME TECHNIQUE - IMPLICATIONS FOR SAFE REENTRY

The application of pesticides using Low-Volume (LV) techniques (volume rate < 50 l/ha) is of growing interest for crop protection in greenhouses. An important LV-technique is the Low Volume Mister (LVM), generating fine droplets (volume mean (aerodynamic) diameter varying from 14 up to 32-mu-m). Field experiments in a commercial greenhouse have been performed to study the decline in concentration of pesticide residue with time for a non-volatile compound (thiophanate-methyl) and a volatile compound (dichlorvos). In addition, indicative measurements were done on rates of deposition. The results indicate a log-linear decrease of the concentration with time. The non-volatile pesticide tends to dissipate faster than the volatile compound. After a six hours period dichlorvos concentrations still substantially exceeded the TLV(TM). Control measures, like venting the greenhouse during one hour, are required for safe re-entry.