Katie Kosanke, Urban Forester, Parks & Recreation, No Phone Number Available
Tuesday, August 12, 2025 at 3:52 p.m.
Powdery mildew has been quite visible this summer which has been causing some concern around town. This fuzzy, white and powdery fungal disease is especially visible on maple varieties with darker leaf color – such as Crimson King. While trees covered completely in powdery mildew surely looks concerning, it is fortunately rarely damaging. At most, new small shoots can be distorted or in rare cases, early leaf drop can happen. Although spores can possibly spread to nearby maple trees – it’s important to note this strain is species specific to a few types of trees – so it won’t spread to your garden, or other plants.
The WSU Extension provides the following recommendations for monitoring and treatment:
Some chemical management options are also available as fungicides are available at most garden centers. While spraying isn’t essential, it can greatly improve aesthetics by reducing the pesky disease. See the WSU Extension website for complete information and recommendation of products. Products should be applied when leaves first emerge – so, don’t bother treating this year, as it is already late in the season. Also, Homeowners should not make foliar applications to trees over 10 ft tall. It is recommended to consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.
The local WSU Extension Master Gardener Program is a great source of information and they can assist homeowners on many tree (and plant) topics. They even have a plant clinic where samples can be brought in for diagnosis! You can contact the WSU Master Gardener Program by phone at 509.477.2181 or by email to mgardener@spokanecounty.org.
