Sick Maple?

Question

Last year my three year old maple got thick white mold on every leaf. What could have caused this? I don't want it to come back this year. I have hundreds of perennials and lots of other trees and shrubs and it was only on this one tree.

Answer 1

It sounds like you've described a disease called "Powdery Mildew". Although it's not often found on most varieties of Maples, it can attack Silver Maple quite severely.

Powdery Mildew spores can over-winter on dead leaves and attack your tree when those humid days begin to appear. Here are some cultural practices you should follow so that your tree doesn't suffer;

1) Remove all fallen leaves in fall/winter
2) Avoid overhead watering on your maple tree--try using a soaker hose rather than sprinkler irrigation. It's better to deep-water than to provide frequent shallow waterings.
3) Make sure you have proper drainage of the soil around your maple
4) Provide proper air circulation within the tree. Too much foilage within the tree itself or too many trees around it will prevent air from circulating and keep it constantly shaded. Therefore, you may have to do some pruning to allow air movement. Shade and high humidity are condusive to Powdery Mildew establishment and growth.
5) Avoid handling the leaves when they're wet.

Once you begin to see Powdery Mildew on your tree, you should spray one of the following; "Bayleton (active ingredient is called Triademefon) or "Triforine (active ingredient is called Funginex). Both are available in most hardware stores and I'd recommend you mix in some spreader-sticker to insure proper coverage. Make sure you spray ALL the foilage!

Also keep in mind that some trees may not be susceptible to Powdery Mildew and there are various forms of Powdery Mildew out there that attack only certain species of trees/shrubs.

Hope this information was helpful. Good luck in protecting your maple tree this year!

-Professional Certified Crop Consultant with over 30 years of experience and a Degree in Plant Science

Answer 2

POWDERY MILDEW:

Causal Agent: Several genera of fungi (e.g., Uncinula, Phyllactinia).

Symptoms: Leaves develop a somewhat "dirty" appearance due to the presence of a white to grayish, powdery growth on the leaf surface. Symptoms are usually first evident on the upper surface of the leaf and can result in premature fall coloration. Unlike many other foliar diseases, powdery mildew typically develops late in the growing season. It can result in defoliation when infection is severe.

Management:
Control of anthracnose, leaf spots, and powdery mildews can be achieved using a multifaceted approach. These diseases are often effectively controlled by following good sanitary and cultural practices and are rarely serious enough to warrant chemical control. Since many of these fungi overwinter on fallen leaves, it is important to rake and remove fallen leaves from the vicinity of the tree in autumn. This reduces the number of spores available to infect emerging leaves in spring or during the following growing season. Tree vigor should also be maintained by proper watering, fertilizing, and pruning. Although foliar diseases are usually considered to be more aesthetic than life-threatening, there are situations where they can be serious and cause permanent damage or even tree death. Newly transplanted trees or trees weakened by stress are particularly sensitive to repeated defoliation. In such cases, chemical control can be beneficial. Among the fungicides registered for homeowner use in Connecticut are thiophanate-methyl, chlorothalonil, and mancozeb. The pesticide label will contain information on dosage rates, application intervals, and safety precautions. Since most of these fungi infect in spring as leaves are unfolding, the first fungicide spray is applied at budbreak. Two or three additional sprays are subsequently applied at 7- to 14-day intervals. Additional applications may also be necessary in unusually wet springs. For anthracnose and leaf spots, once symptoms are visible on the leaves it is too late for chemical control. (The exception to early-season infections are the powdery mildews. They usually infect in mid-season so applications of fungicides for control would be applied as soon as symptoms are visible.)