Identification of powdery mildew species in cucumbers and tomatoes in greenhouse and validation of control methods

Abstract: Powdery mildew is the main disease observed in tomatoes and cucumbers in
greenhouses in Quebec, Canada. Control of the disease is problematic for many producers
across the province and cause severe damages. The first objective of the project was to identify species of powdery mildew in tomatoes and cucumbers in Quebec greenhouses. The second objective was to evaluate the effectiveness of control methods already available against the disease to propose effective pest management strategy. Powdery mildew was monitored in 14 greenhouses in 2020 and 2021. Two species were observed in tomatoes, Oidium lycopersici and Neoerysiphe hiratae and Podosphaera xanthii in cucumbers. Fungicides treatments were applied in 50 to 100 % of the greenhouses by producers in 2020 and 2021, with seven different products in cucumbers and four in tomatoes. The disease was controlled in 67 % of cucumber greenhouses and 82 % of tomatoes. In 2022, four biopesticides, two different application of UV lamp and two control (water and conventional fungicide) were tried against O. lycopersici and P. xanthii in experimental greenhouses. In cucumber, citric acid and UV lamp significantly reduced the severity of powdery mildew. Phytotoxicity was however observed with UV lamp, and the reduction with both products was less effective than the conventional fungicide. In tomato, sulfur reduced the severity of infection, but not as effective than the conventional fungicide. Those results will help producers to choose the best strategy against powdery mildew in tomatoes and cucumbers.