Controlling Powdery Mildew Organically in an Apple Tree

Apple trees can develop the fungal disease known as powdery mildew.

Powdery mildew is a fungal disease that strikes many different types of plants. The pathogen known as Podosphaera leucotricha causes the fungal spores that result in a white, fuzzy coating on apple tree leaves. When a tree is infected, its new growth is often stunted and distorted. The amount of fruit the tree produces can be seriously affected, and fruit that does set is often reddish brown and stunted. You can do several things to prevent this disease and after it strikes, you can treat it with organic methods.

Things You'll Need

• Pruning shears or clippers
• Sulfur
• Spray apparatus
• Milk
• Water
• Biological control (optional)

Instructions

1. Prevent powdery mildew by planting your tree in an area where it will have good air circulation. Do not plant an apple tree closer than 15 to 20 feet of other apple trees or any kind of large plant. You can also keep your apple tree well pruned to enable it to receive good airflow among its branches.

2. Prune infected shoots on your apple tree when it is dormant in winter. You can use garden clippers or your fingernails to pinch off the ends of twigs and branches that have a fuzzy white coating. Dispose of these infected shoots by bagging them tightly and sending them to your landfill.

3. Spray infected trees with organic sulfur as soon as you notice the powdery mildew problem. Spring is a good time to spray, but you can perform this operation at any time. Sulfur comes in several different forms and is sometimes combined with lime. Follow label instructions on your product for correct mixing and application.

4. Spray your apple tree with a combination of whole or skim milk and water. Mix ½ cup milk in 1 gallon of water and pour it into a sprayer that is strong enough to reach the top of the tree. Many people believe that this folk remedy works against powdery mildew because the milk's lactobacillus spores form colonies on the apple leaves, out-competing the powdery mildew spores.

5. Use a biological control if possible. Oregon State University's website describes two strains of Bacillus, which are bacteria gathered from soil, water and decomposing plants. The products Serenade MAX and Sonata contain these bacteria and are reportedly effective in controlling powdery mildew on apple trees and other plants.

Tips & Warnings

• Prune your tree in the fall or winter when it has lost its leaves and entered its dormant period. Always cut dead or damaged branches back to the trunk and always take care not to cut into the trunk or branch collar.

• Serenade MAX and Sonata are available commercially at selected nurseries and online sources. Organic bacillus products can be expensive, with Serenade costing $169 for a 12-pound bag through one online distributor.

• Do not use sulfur spray on your apple tree if the temperature is 90 degrees F or above.

References

• University of California, Davis: Apple: Powdery Mildew
• Colorado State University: Some Pesticides Permitted in Organic Gardening
• West Virginia University: Disease Management Guidelines For Organic Apple Production In Ohio
• U.S. Envrionmental Protection Agency: Bacillus Subtilis Final Risk Assessment
• Oregon State University: Apple---Powdery Mildew Control

Resources

• Weekend Gardener: How to Prune an Apple Tree