How to Fix Powdery Mildew on Trees

Powdery mildew forms a white or gray powderlike substance on leaves and new shoots. Although it rarely kills the tree, it disfigures the leaves and makes the tree much less attractive. Preventing powdery mildew is easier than eradicating it once a tree is infected, but the problem can be fixed with proper cultural management and time. Fungicides are the most common treatment for existing powdery mildew infections, but steps must be taken so it doesn't return.

Things You'll Need

• Fungicide
• Pruning shears

Instructions

1. Apply protectant fungicides to trees at the first sign of a powdery mildew infection. Apply it to all surfaces of the tree following label instructions and treat the tree with further applications yearly.

2. Use eradicant fungicide if the powdery mildew infection is severe. Apply following label directions and repeat as indicated until the powdery mildew is under control.

3. Thin trees if possible to provide more sunlight to the plants. Avoid planting trees too close together or in areas that receive more shade than indicated for the tree type.

4. Prune away old branches to provide ample air flow and light to the interior of the tree's canopy, where powdery mildew is likely to grow. In a healthy tree, trimming away infected branches may be adequate to fix the powdery mildew problem.

5. Mist the tree leaves with water each morning during spring and summer to wash away any powdery mildew spores. Rinse after the sun has risen so the leaves quickly dry, otherwise other fungal problems may surface on the wet leaves.

Tips & Warnings

• There are both organic and chemical fungicides available that target powdery mildew.

• There are some trees that are resistant to powdery mildew. Plant these if your area is prone to mildew infections.

• Overfertilization can also make trees susceptible to powdery mildew.

References

• University of California Extension: Powdery Mildew