Comparative efficiency and residue levels of spraying programs against powdery mildew in grape varieties

Powdery mildew (Erysiphe necator Schw.) fungal disease in vineyards is becoming an increasingly important concern due to climate change and the emergence of resistant populations after heavy spraying. Recently, new disease control methods based on phenological development, disease development, and meteorological data have been established in Türkiye. These models can provide sufficient protection with minimal fungicide use and minimize residue problems due to excessive fungicide use. In this study, the activities of the UC Davis risk index model, decision support strategy (DSS) models, and classical model, based on plant phenological development stages suggested by the Turkish Ministry of Agriculture and Forestry, were used to protect against powdery mildew. Three alternative control strategies were investigated for 2 years using two grape varieties. In addition, the amount of pesticide residue in the final product by the spraying models was also evaluated. The UC Davis risk index model was applicable in places with similar climatic conditions, such as Bursa Province, and showed better results than other spraying programs. Although the classical model proposed by the Ministry of Agriculture and Forestry is generally less effective than the UC Davis risk index model, once less spraying achieved high effectiveness rates each season. The UC Davis risk index model considerably lowered the disease incidence rate in clusters below the 5% limit. The DSS model provided poorer protection than the other two models evaluated in this study. Among the fungicides with active ingredients, thiophanate-methyl, kresoxim-methyl, and penconazole, only thiophanate-methyl exceeded the 0.1 ppm (mg/kg) limit specified in the European Union Pesticide Maximum Residue Limits and Turkish Food Codex Pesticide Maximum Residue Limits for both grape varieties. Alternating fungicides with different active ingredients instead of a single fungicide at regular intervals throughout the season can reduce residue problems of grapes and the risk of pathogen resistance to fungicides.