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Diseases in dogwoods

POSTED: June 5, 2013 4:00 a.m.

The flowering dogwood, or Cornus florida, is a popular species of tree in home landscapes all over Georgia. It is native to the southeastern United States and is well adapted for many landscape locations.

However, flowering dogwoods are still susceptible to some fungal diseases. Fortunately, these can be managed to prevent long-term damage.

Powdery mildew is a fungal disease that appears on leaves and new shoots of dogwood trees. New growth becomes covered in a ‘powdery' white coating, most often on the upper surface of the leaves.

As the disease spreads, dead spots will appear on the leaves, as well as "scorched" areas around the leaf edges. Heavily-diseased leaves may turn yellow and drop to the ground. Trees planted in shady areas with poor air circulation are more prone to powdery mildew.

Powdery mildew normally shows up later in the year, but if found in the spring, fungicide treatment is suggested.

Fungicides containing the active ingredients propiconazole and myclobutanil will provide some control over powdery mildew spread. Dead and diseased material should be removed from the tree as soon as possible to prevent spreading to young leaves.

Spot anthracnose is another common fungal disease of flowering dogwoods. This disease attacks flowers and leaves, especially during wet spring weather. Spot anthracnose spots are tan with purple or red borders. Flowers and leaves can become distorted by heavy infections.

In most cases, spot anthracnose will not result in severe damage, but repeat infections in successive years can weaken a tree. To lessen damage, thin the canopy to increase air circulation. If spotting is severe, fungicides may be used at bud break and continued until the tree is fully leafed-out.

Dogwood anthracnose is a fungal disease that is most significant only in areas of Georgia more than 2,000 feet. It is a serious disease capable of killing several trees, and most species of dogwoods are susceptible. Symptoms appear in the spring with spots on leaves and flower petals. Dogwood anthracnose spots will show up as tan with purple edges, brown leaf margins or large blotches.

Drooping leaves hanging from twigs can be seen in early spring during cool, wet conditions. The fungus will then spread to the stems and trunk, causing sunken cankers in the bark. These cankers can girdle and kill individual branches, and even the entire tree.

Dogwood anthracnose can be managed if caught before branch dieback occurs. During dry summer conditions, prune out all dead or cankered material. Rake up and dispose of fallen leaves. Thin the canopy to improve air flow. Avoid high amounts of nitrogen fertilizer.

Fungicides can provide protection to new leaves when applied in the early spring. There are even some resistant varieties of dogwood now available, which are usually hybrid crosses of flowering dogwood and Kousa dogwood.

Clark MacAllister is the Dawson County extension agent. For more information, call (706) 265-2442.

 

 

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