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Watch for Downy Mildew in Leafy Vegetables

November 18, 2019
This agronomic image shows downy mildew in lettuce

Seasons with high moisture in AZ growing regions can lead to higher pressure from downy mildew in leafy vegetable crops. Damp and cool weather creates the perfect conditions for downy mildew to develop in your crops, so it is important to recognize the threat posed by this disease and implement management strategies when needed.

Downy mildew is caused by the pathogen Bremia lactucae. Wind spreads spores from plant to plant, and cool temperatures and moisture on the leaf surface create the environment for this disease to develop. This disease causes green to yellow spots on the upper side of leaves and white, fluffy growth on the lower side. If left unchecked, severe infections can kill leaves.

Chris Clemens, Syngenta agronomy service manager for the Western US, discusses how weather can impact the threat from downy mildew on AZ’s leafy vegetable crops.

Managing downy mildew

This complex pathogen is constantly evolving, making a proactive resistance management plan vital. Resistant varieties are a key management tool, and they should be utilized along with a rotation of fungicide sites of action for the best control.

When downy mildew risk is high, Syngenta recommends Orondis® Ultra fungicide for excellent control of the disease. Orondis Ultra features 2 active ingredients that are highly active against Oomycete diseases like downy mildew. Revus® fungicide is an efficacious choice as well, while Actigard® 50WG fungicide activates the plant’s natural defense systems to protect itself against diseases.

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