Caring for Crape Myrtles: Powdery Mildew Treatment

Depending on your region, one of the biggest challenges to growing happy and healthy crape myrtles can be battling mildew. Let's take a closer look at the cause of the problem, how to avoid mildew on a crape myrtle and how to treat the mildew once it becomes a problem.

Know Thine Enemy: Powdery Mildew Fungi

The powdery mildew that appears on crape myrtles in the spring is one of two types of fungus: Erysiphe australiana or Phyllactinia guttata. According to Oregon State University's Guide to Plant Disease Control, the fungi wait out the winter dormant on the young tissues of last years new growth and leap into the action when other fungi land on the plant the early spring. The white, dusty growth of the fungus then infects the crape myrtle, causing the loss of leaves and unsuccessful flower buds.

An Ounce of Prevention: Avoiding Powdery Mildew

As is the case with most things, it's best to avoid the try to avoid powdery mildew before it appears, if you can. One good tip for Oregon State is to plant your crate myrtles with enough open space around them to ensure good air circulation. If you've had powdery mildew plants on your crape myrtles before, it's a good bet they'll be there the next year, and it's worth treating the likely problem areas with either fungicide or your favorite organic alternative as soon as new spring growth starts and before the the fungus even rears its head.

A Pound of Cure: Treating Powdery Mildew

Once you've noticed a powdery mildew infection on your crape myrtles, it's time to whip out the fungicide. If you're gardening green and organic, I'd recommend asking a master gardener what he or she suggests as the most environmentally friendly approach. Otherwise, you may need to apply the fungicide to the infected areas until the new growth is finished for the year. Bare in mind that fungicides can often retard the flower blooming process and can cause an infection of mites, which were previously kept at bay by healthy levels of fungi.

Mildew Resistant Cultivars

Perhaps the most effective method of avoiding mildew problems with our crape myrtles is to select varieties that are particularly resistant to mildew. One of the most mildew resistant crape myrtle cultivars of all is the Sarah's Favorite crape myrtle, an upright specimen that grows around 20' tall and has fairly symmetrical bunches of white flowers. Some other mildew resistant crape myrtle varieties include Sioux, Tightwad Red, Zuni and Acoma, to name just a few.

Sources:

http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=1315

http://en.allexperts.com/q/Perennials-729/Powdery-mildew-crape-myrtle.htm

http://msucares.com/newsletters/pests/infobytes/19980519.htm