Keeping powdery mildew in apples under control

In short... 

• Spot and stop early: Learn when and where powdery mildew attacks to protect leaves, fruit, and terminal buds. 
• Protect new growth: Apply timely IPM and fungicide strategies during rapid growth to prevent infections from taking hold. 
• Plan for the season: Rotate fungicides and use long-term cultural practices to safeguard yield and maintain fruit quality year after year. 

Powdery mildew continues to challenge even the best-managed orchards. An IPM approach combining cultural and chemical strategies remains key to maintaining fruit quality and long-term orchard success. 

Powdery mildew remains a perennial challenge for Canadian apple growers, despite careful orchard management.  

Caused by the fungus Podosphaera leucotricha, this disease attacks the leaves and fruit of apple trees, causing a white, powdery growth that can affect tree development and leave fruit unmarketable. Because the fungus overwinters in infected buds, it’s ready to strike as soon as new growth begins each spring.  

For apple growers across Canada, understanding and managing powdery is essential to protect tree vigour, overall yield and fruit quality season after season. 

Get to know it, so you can control it 

Powdery mildew infections begin in the spring, and infections can occur from about three weeks before bloom to three weeks after bloom. Both leaves and fruit are susceptible to infection. Leaf infections can cause reduced photosynthetic ability, potentially leading to smaller fruit, while fruit infections can cause russeting or mis-formed fruit.  

Powdery mildew can have multiple generations per growing season, meaning it spreads throughout the season. Trees are susceptible as long as they are actively growing. This is known as before terminal bud set and if terminal buds are infected, the disease can quickly affect the tree and fruit again the following season. Due to the perennial nature of powdery mildew and its ability to infect multiple sites, it’s important to establish disease control between tight cluster and bud set to prevent powdery mildew infections from overwintering in the terminal bud. 

The disease thrives in moderate temperatures (10-25°C) and high relative humidity. These ideal weather conditions typically occur near the end of the primary scab infection window, making it essential to protect trees from powdery mildew, even when scab may be the management focus.  

Controlling powdery mildew

It’s essential to protect trees against powdery mildew during the stage of rapid new growth – from the tight cluster stage until the terminal buds have set – especially if weather conditions are favourable to disease development. This can include fungicide applications on a regular basis to provide necessary control.

Since powdery mildew fungus overwinters in terminal buds, growers must take an annual approach to managing the disease. This includes a long-term minded integrated pest management (IPM) program that includes cultural and chemical control methods.

The rotation of fungicide FRAC groups, including the use of sulphur and cultural control practices, like pruning and variety selection are key to long term success of apple orchards. 

Syngenta Solutions  

With an effective and flexible lineup of fungicide control options, Syngenta supports the management and control of powdery mildew while providing control of apple scab (Venturia inaequalis), as these diseases commonly overlap in infection timing.

*Suppression 
**Use rate for apple scab 

How can these tools be used in your integrated pest management program?  

• Applying Inspire Super (Group 3) early in the growing season offers growers a head start on disease prevention while saving other FRAC groups for later in the season. 
• Apply Aprovia Top (Group 7) at pink and bloom stages for powerful scab and powdery mildew control. 

The management of powdery mildew should be approached with a long-term mindset, covering new tissue during rapid growth, and ensuring terminal buds are free of infection. Syngenta is proud to offer Aprovia Top and Inspire Super to help growers battle this disease. For more information, reach out to your local inputs supplier or talk to your local Syngenta rep.  

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