by Dr. James H. Blake, Director, Home & Garden Information Center, Clemson University, 2009
Hi, I'm James Blake, Director of the Clemson Extension Home & Garden Information Center. Today we're looking at powdery mildew on dogwood.
We're in the South Carolina Botanical Garden on the campus of Clemson University back in front of a dogwood that we visited just six weeks ago that was severely infected with the disease known as spot anthracnose. Today it is severely infected with another disease known as powdery mildew. In the southeast, powdery mildew on dogwood is known to be caused by two different fungi, Microsphaera and Phyllactinia.
There are many powdery mildew diseases on many of the different plants that we grow but they don’t go back and forth across the different species. They are generally host specific.
The disease gets its name from this white, powdery-like growth that is on the upper leaf surfaces and the young shoots. This white material consists of the fungus body, the mycelium, and the numerous spores that it produces that are easily spread by the wind.
Young leaves with severe infection can be stunted and deformed. Older leaves may have just a purplish discoloration on the upper leaf surface. In the case of severe infection you may also see some dead spots on the leaves or some marginal browning. Early leaf drop may also occur.
Favorable conditions for this disease are warm days, cool nights and high humidity.
In the fall, these fungi produce over-wintering structures that survive the cold temperatures and are there next spring and produce spores to initiate new infections in the spring.
To manage this disease, you can rake up and destroy fallen leaves. You should also choose resistant varieties such as 'Jean's Appalachian Snow', 'Karen's Appalachian Blush', and 'Kay's Appalachian Mist'. There are also varieties of Cornus kousa that are resistant.
We don’t recommend homeowners try to spray fungicides on these very large trees. You don’t have the proper equipment and it’s difficult to get the adequate coverage to manage the disease. If you would like some information on fungicides if you have a specimen plant, check out our Dogwood Diseases and Insect Pests fact sheet on the Home & Garden Information Center web site.
For more information on gardening, landscaping, insect and disease problems on your plants, visit the Home & Garden Information Center web site at www.clemson.edu/hgic.
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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.