Rainfall brings plant life much needed relief of summer temperatures. However, an abundance of moisture in a short period of time can have side effects, especially in the case of the fungal pathogen anthracnose on Panhandle dogwoods.
The flowering dogwood, Cornus florida, is a native to North America and a landscape favorite in southern states. Dogwoods are readily available for purchase at virtually any garden center and once planted, quickly thrive in our environment. However, disease management can be an issue in the spring and fall, when cooler temperatures emerge, coupled with extended periods of heavy rainfall. We’ve had an anomaly of recent, as a similar condition has arose this summer with rainfall surpassing 10 inches in some areas, within 30 days or less, as temperatures have slightly dipped.
Anthracnose may be the most concerning issue in our region, regarding dogwoods. Anthracnose is a common fugal pathogen that can be found in flowering plants, shrubs, trees, vegetables and even field crops. Older trees with less vigor, and stressed trees are the most affected. Trees and other plants can be treated for the disease, but consecutive years of infection with inadequate care can cause demise.
There are two types of anthracnose that can affect dogwoods, spot anthracnose and dogwood anthracnose. Spot anthracnose is caused by the fungus Elsinoe corni. The disease produces small, rounded purple areas on dogwood leaves (figure 1). Spot anthracnose is sometimes considered more of a cosmetic issue, and does not usually have adverse impacts, if treated. However, dogwood anthracnose is caused by the fungus Discula destructive. This disease is much more severe and can lead to mortality. Symptoms of dogwood anthracnose are leaf lesions, which are blotchy in pattern, to twig blight and stem canker. Young leaves are very susceptible.
What can be done to curb an anthracnose infestation in dogwoods? Taking rainfall events and irrigation scheduling into consideration is a helpful management measure to avoid excess moisture in the environment. An automated irrigation system should have rain sensors to help manage moisture levels. Avoid overhead watering during cool seasons as well.
What if anthracnose has been diagnosed in dogwoods? First, prune all dying or dead limbs, twigs and leaves. The next step is to protect new tissues of expanding leaves and twigs from fungal activity. Spray an application of a systemic fungicide labeled to control dogwood anthracnose. Fungicides containing propiconazole or tebuconazole are recommended. Fungicide products marketed for roses, flowers and shrubs tend to have one of these chemicals in the formula. After at least two weeks of the application, apply a protectant fungicide labeled to control dogwood anthracnose. Fungicide containing chlorothalonil are particularly effective. Be sure to cover the entire tree with the applications. This is essential to control the fungus.
Other conditions like crown canker or collar rot, as well as powdery mildew are also associated with lingering wet, cool conditions. An effective management plan always begins with an accurate diagnosis. Please contact Gulf County Extension at 639-3200 for more information.
Supporting information for this article is from the UF/IFAS EDIS publication: “Cornus florida: Flowering Dogwood” by Edward F. Gilman and Dennis G. Watson: http://edis.ifas.ufl.edu/pdffiles/ST/ST18500.pdf and the University of Arkansas Extension publication, “Anthracnose Diseases of Dogwood” by Sherrie Smith and Janet Carson: https://www.uaex.edu/publications/pdf/fsa-7564.pdf
UF/IFAS Extension is an Equal Opportunity Institution.