A trial evaluating new biological and synthetic fungicides for stemphylium leaf blight control in onions aims to find solutions to strengthen resistance management strategies for this disease.
The current season trial, which is co-funded by A Lighter Touch and Onions New Zealand, is being harvested, and results are pending. Seven biological and five synthetic control options have been evaluated through the trial which is located in Pukekohe.
Stemphylium leaf blight is a foliar disease that New Zealand onions growers have combatted for several years. In bad seasons, losses to onion crops can be considerable, severely impacting both quality and yield.
Following feedback from growers that they were not seeing the expected level of control from several fungicide products used to help prevent and manage stemphylium infection, Onions NZ and Plant and Food Research completed extensive sensitivity screening of fungicides to stemphylium.
Credit: Onions NZ.
Results from this work showed resistance was found in three modes of action and was detected across all growing regions. Remaining effective control options are limited, and strong resistance management is required to protect the remaining chemistry. An industry-led strategy, developed with support from registrants and PFR, was communicated to growers last winter and have informed crop protection programmes for the current season.
However, with only two registered options for control of stemphylium, the ability to rotate chemistry to achieve disease control and follow resistance management guidelines is limited.
Cultural practices, such as managing water stress, correct nutrition and reducing pressure from other pests and diseases, are important components of prolonging the life of existing chemistry, and finding alternative control options will also be a key element in further refining onion spray programme development.
Results from the trial will provide onion growers with a guide to what successful candidates could be incorporated into spray programmes, and will also be shared with all ALT partners.
