I’ll be the first to admit that I’m not the most observant person — there is plenty that gets past me. Because of this, I quickly realized that the crape myrtles are having a tough time with powdery mildew this year. There is plenty that I miss going 60 miles per hour down the road, but the grayish tips on these ornamentals isn’t one of them.
As the name suggests, the disease is characterized by a powdery grayish fungus. It has been most evident to me on the young, tender shoots at the tops of the plants and the new root suckers emerging at the base of the plants. Often this new growth will become distorted and misshapen. If flowers become infected, in more severe cases, the blooms could fail to open. The disease is very evident on many ornamentals besides crape myrtles. Dogwoods, euonymus, oaks, phlox, monarda and many others also can be susceptible.
The development of the powdery mildew fungus, Erysiphe lagerstroemia, is favored by dry, sunny days followed by cool, moist nights. As you might imagine, as spores mature, they are easily dispersed to surrounding plants by wind, rain and insects. Interestingly, unlike many other landscape diseases, powdery mildew does not require the crape myrtle leaves to be moist for infection to occur.
Prevention goes a long way with powdery mildew, as with other landscape problems. Always plant crape myrtles in full sun. Additionally, when establishing a new planting, consider purchasing resistant varieties.
In our local garden centers, cultivars with good resistance to powdery mildew are available. Some of these include “Dynamite,” “Red Rocket,” “Tonto,” “Tuscarora,” “Natchez,” “Zuni” and “Muscogee.”
There are many crape myrtle varieties to choose from. Consider visiting the website of one of our Southeastern land grant universities for a more comprehensive list. These links include information about plant size, flower color and disease resistance: athenaeum.libs.uga.edu/bitstream/handle/10724/12262/C944.pdf (University of Georgia), clemson.edu/extension/hgic/plants/landscape/trees/hgic1023.html (Clemson) or edis.ifas.ufl.edu/mg266 (University of Florida).
If your crape myrtles are already established, determine if there is any selective pruning of the crape myrtle — or other nearby trees — that might improve light penetration and air flow. Remove the tender sprouts, or suckers, at the base of the plant. Since this new growth is particularly susceptible to the fungus, it can quickly move up into the tree canopy. Remove and dispose of other diseased stems and branches, if the disease has progressed too far.
Fungicides can be applied, but are most effective when applied at the first sign of the disease. Choose products containing active ingredients such as chlorothalonil (found in Daconil, Ortho Garden Disease Control, Fertilome Landscape & Garden Fungicide, etc.), myclobutanil (found in Spectracide Immunox Fungicide, Spectracide Multi-purpose Fungicide, etc.), or sulfur (found in Safer Garden Fungicide, Bonide Sulfur Plant Fungicide, Hi-Yield Wettable Dusting Sulfur). Remember, the trade names aren’t the important part; the active ingredients are. If your favorite garden center doesn’t carry the tradenames mentioned, check the front of the label, usually on the lower left side, for the ingredients.
As always, follow the directions on the label. Contact your local county extension office if you need any more information on this or other topics.
Bibb County Master Gardeners will be at Macon Ace Hardware stores (6173 Houston Road, 3600 Riverside Drive and 5020 Forsyth Road) to help with your gardening questions from 9 a.m.-noon June 25.
Contact county Extension agent Karol Kelly at firstname.lastname@example.org.