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Be aware: Powdery mildew plagues dogwood trees
0424POWDERY-MILDEW
Powdery mildew is a fungus that coats a tree’s leaves.

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Just the other day, I was looking at a dogwood tree at the house and saw it was in pretty good shape.

However over time, things change, making it worth keeping an eye on the tree to see if it becomes infected.

Three main foliar diseases that dogwoods tend to get this time of year. I’m going to focus on one this week.

Powdery mildew is a fungus that shows up not only on the tree’s leaves but on its tender shoots. New growth becomes covered in a white coating usually on the upper surface of the leaves.

As the disease progresses, the leaves tend to look scorched along the edges or have dead patches. They also yellow out and drop off the tree.

The disease is very common in a dense, shady area with poor air circulation.

Usually when we see powdery mildew, they come late in the year and generally do not pose a big threat to the plant’s health. But when they are present in the spring — as it does on dogwood — the disease should be treated with a fungicide.

Before going straight to chemical warfare on the disease, try some things to discourage it. Start by raking up and getting rid of all fallen leaves. Prune out dead and infected branches. If you can, improve air circulation and sunlight by removing overhanging branches.

If disease is severe enough to warrant the use of fungicides, be sure the dogwood is a valuable specimen and the spray equipment can provide good coverage. Very effective fungicides for dogwood powdery mildew control include myclobutanil and propiconazole. Some control can also be obtained with thiophanate methyl.

Product labels will provide information on how often to spray. When powdery mildew persists and sprays are repeated, it is recommended to alternate fungicides to decrease the chance of fungi developing resistance.

Resistant species and cultivars are available and should be considered for new plantings. Cultivars of the oriental dogwood Cornus kousa such as “Milky Way,” “Milky Way Select,” and “National” and Cornus florida x Cornus kousa hybrids such as “Aurora,” “Constellation,” “Celestial” and “Stellar Pink” are generally resistant to powdery mildew. The flowering dogwood (Cornus florida) cultivars “Appalachian Joy,” “Appalachian Blush,” “Appalachian Snow” and “Appalachian Mist” are very resistant to powdery mildew.

Check out next week’s column on the disease spot anthracnose.

Michael Wheeler is county extension coordinator for the UGA Cooperative Extension office in Hall County. You can contact him at 770-535-8293, www.hallcounty.org/extension. His column appears weekly and on gainesvilletimes.com/life.

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