Powdery mildew is rarely fatal to mature trees, although it can cause weak foliage development and create an ugly appearance. The mildew can cause major damage to young trees, though, as they simply don't have enough leaf surfaces to support them through an infection. An infected tree will have white or gray powdery growth on the leaves, which prevents proper photosynthesis.
1. Crown Thinning
Poor air circulation helps powdery mildew spores thrive, so annual pruning is one of the best defenses against the fungus. For trees, late winter is usually the best time to prune with the goal of opening up the crown. Your tree service may remove up to a quarter of the smaller branches in the tree canopy, taking out any that are growing too closely or rubbing together. This will allow more air to circulate around the remaining branches.
2. Overlap Prevention
Overlapping crowns of neighboring trees will also reduce air circulation while also making it easier for mildew spores to spread between the trees. Cutting back the branch length during pruning can eliminate overlap. Generally, a branch can be cut back by about a third of its length if necessary, so it's possible to trim back both trees enough so that their branches aren't in contact with each other.
3. Disease Removal
Branches that are already host to a severe powdery mildew infection may not be salvageable, especially on young trees. If the leaves are already beginning to die off and shrivel, then it's often necessary to trim back the most affected sections of the branches to remove the worst of the mildew. This will minimize the amount of spores being produced in the crown, which can help slow the spread of mildew.
4. Tool Sanitation
Sanitation when pruning mildew-infected trees is a must, otherwise, the disease will be spread around to healthy leaves. The simplest way to keep your tools sanitized is to dip them in a dilute bleach solution after each cut or to wipe them down with an isopropyl alcohol solution. After pruning, all the trimmed-off material should be raked up and disposed of to prevent the spread of fungal spores.
5. Fungicide Application
If trimming the tree isn't enough to clear up powdery mildew, then a fungicide treatment is necessary. Many fungicides aimed at destroying powdery mildew contain sulfur compounds, which kill the fungus and spores on contact. These must be applied early in the infection in order to be most effective.
Contact a tree service in your area if you have trees suffering from powdery mildew growth.
After thinking about how to keep some of the flowers in my yard alive, it occurred to me that we had some real problems on our hands. For starters, we had a bunch of overgrown trees that needed to be dealt with. The second thing we had to take care of was the fact that we were really behind on basic yard care. I started talking with friends and neighbors about what they did to make things better, and they recommended a local tree service company. After they came out and made some changes, my yard was gorgeous. Learn more about tree care on my blog.