Issue 12, September 22, 2021

Septoria Leaf Spot on Dogwood

Photo 1 Suspected septoria leaf spot on midwinter fire bloodtwig dogwood

I recently came across a planting of midwinter fire blood-twigged dogwoods heavily damaged by septoria leaf spot, a common fungal disease of dogwoods in our area. Several Septoria species infect dogwoods. The bloodtwig dogwood (Cornus sanquinea) is a host to Septoria cornicola and Septaria cornina, with the latter more common in North America (Farr 1991).

The disease typically appears as circular, angular or irregular shaped spots with olive-gray to brown centers surrounded by dark purple or reddish borders. Septoria spots are similar to but larger than those of spot anthracnose on flowering dogwood, reaching about 1/4 inch in diameter. Heavily infected leaves often turn yellow and prematurely drop from the plant. Fortunately, septoria leaf spot does not seriously harm dogwoods. The damage is mainly aesthetic, as the resulting spotted foliage and partially defoliated shrubs are not very attractive

Septoria overwinters in leaf litter left around the plant. Wind and rain spread the pathogen’s spores to susceptible plant tissues. Symptoms become evident near the end of summer and are more common in wet conditions or high humidity.

Rake and dispose of leaf debris to help reduce the potential for future infections. Most people can tolerate septoria leaf spot on dogwoods without any fungicide sprays. When justified, septoria may be treated preventatively with a Chlorothalonil, Chlorothalonil + propiconazole, Myclobutanil, or Thiophanate-methyl. Begin sprays at bud break. Two to three more applications may be needed at 14-day intervals if conditions are favorable for disease development.

Travis Cleveland

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