Preventive fungicide sprays for Phytophthora infestans using drift-reducing techniques

Preventive fungicide sprays are vital for protecting potatoes against Phytophthora infestans. Recent research funded by BO Akkerbouw shows drift-reducing nozzles and pulsed nozzles (PWM) can match conventional methods. Seven techniques were tested, including nozzles with 50%, 75%, and 90% drift reduction, lowered boom height, air assistance, and drag cloths (e.g. Wingspreader, Wave). Trials included a controlled spray booth and real-world field conditions. Inoculation with spores measured infection levels and spray coverage. Lower dosage in the booth highlighted differences; field trials used label-recommended rates. Spray volume (200 or 300 l/ha) had minimal impact except for the 90%-drift-reducing Lechler ID3 nozzle, which performed better at 300 l/ha. PWM nozzles matched conventional nozzles when properly selected, with knoet nozzles outperforming injection types. Protection declined significantly over time: top leaves showed reduced protection after 7 days, and by 11 days, protection was substantially reduced across all leaves. Drag cloth use showed lower effectiveness on upper leaves in the booth due to crop contact, but field results were comparable as contact was limited to plant tips. Illustrated: potato plant in spray booth, field application, and untreated infected leaf. Contact: gerrit.vansteenebergen@wur.nl; K.Wilhelm@delphy.nl; www.wur.nl; www.delphy.nl. FEDCOM WAGENINGEN UNIVERSITY & RESEARCH BO