A particular fungal spore is responsible for the developing emergence of white fungus on dogwood trees. Though the culprit, powdery mildew, attacks a wide variety of hosts, its history with dogwoods is not longstanding. For example, this fungal infection did not begin to appear on flowering dogwoods in Virginia until 1993. Fortunately, effective control methods are available.
Vigorous flowering dogwoods are less likely to fall ill to powdery mildew than weakened or stressed trees. Plant your flowering dogwood trees in areas that provide full sun to light shade; extreme shade creates sparse foliage and dull color, according to the University of Florida IFAS Extension. Grow these trees in the nutrient-rich, moist, well-drained loam or sandy soil they prefer with the addition of organic content.
Powdery mildew affects many ornamental trees, but on flowering dogwoods, the particular fungal pathogen is Microsphaeria pulchra. This fungus spreads sporadically on the wind from infected sites to new leaf growth on dogwoods during spring. Ideal conditions for germination include high moisture content with warm daytime temperatures and cool temperatures at night, according to the Virginia Cooperative Extension. Trees kept in the shade are also more susceptible.
Symptoms and Damage
A white mildewlike fungus develops on the surfaces of leaves and flower buds on infected flowering dogwood trees. As the disease progresses, the white substance becomes more pronounced and leaves may turn red, experience stunted growth, wilt or curl, according to the Virginia Cooperative Extension. Damage includes potential stunted growth of the root system as well as of the entire tree if infection persists for several years.
Planting resistant flowering dogwood varieties offers reliable control. Even though "resistant" does not mean trees are immune, the chance of infection is greatly reduced. Resistant options include Cherokee Brave and Sweetwater Red, according to the Virginia Cooperative Extension.
For chemical control of powdery mildew white fungus on flowering dogwood trees, apply a fungicide formulated for use on dogwoods with an active ingredient of triadimefon, trifloxystrobin or neem oil extract, according to the Virginia Cooperative Extension. If in need of assistance, contact your county extension agent.