How do I treat a powdery mildew infected plant/tree?

Asked August 5, 2015, 9:43 PM EDT

I have aspen trees in my backyard. Every year about this time of the year the leaves develop powdery mildew. I practice good hygiene by removing all the leaves that drop and in the fall. I don't fertilize the trees at all. I water in the morning so that everything has a chance to dry out.

What do I do to treat the powdery mildew on my trees and/or any other existing plant in the garden? Or do I just learn to live with it?
Thank you.

Arapahoe County Colorado trees and shrubs

1 Response

Powdery mildew is a fungus that can occur on aspen trees and many other landscape plants.

Powdery mildews overwinter on leaf debris as partially developed spores. As spring arrives, the spores mature and are released. Spores are blown or splashed onto newly emerging foliage where they germinate on the leaf surface. So it is very important to rake up the leaf debris in the fall and get rid of it. Do not put the leaves in your compost pile if you have one, home compost piles rarely get hot enough to kill the fungus.

Fungicides labeled for use on powdery mildew can be used, but will not improve already affected leaves. Alternative chemical controls include neem oil or a combination of baking soda and horticultural oil (e.g. 1 tbsp. baking soda plus 2.5 tbsp horticultural oil per 1 gallon of water.) Be sure to read the label carefully and use only as directed.

Certainly the size of your tree will determine how easily it can be sprayed with any substance. Powdery mildew rarely kills a tree and good cultural practices especially in the fall may help to reduce repeat outbreaks.

Here is a fact sheet on powdery mildews:

http://www.ext.colostate.edu/pubs/garden/02902.html

Other plants that have powdery mildew are treated in a similar fashion. Cultural practices are important regardless of the species of plant, remove and destroy all leaf matter from plants that have powdery mildew.