Posted by Brent Wilson on 8/1/2017 to FAQ (Frequently Asked Questions)
If during summer some or all of the leaves on your crape myrtle bush or tree are developing small spots and turning red and prematurely dropping from the plant this is most likely Cercospora leaf spot. This condition usually occurs during hot summers with more than average rainfall. While some crape myrtle varieties have more resistance to the spot than others all can be affected during an unusually rainy and wet summer.
Cercospora Leaf Spot
The Cercospora leaf spots form on crape myrtle and other types of plants due to water drops from rain or irrigation that sit on leaves during hot and humid conditions. This is especially true in large plant nurseries and residential or commercial landscapes that use overhead irrigation frequently. When using overhead irrigation it is best to water in early to mid morning so the sun can dry the water from foliage.
While Cercospora leaf spot rarely if ever kills the target plant, heavy spotting and/or discoloration of the leaves and premature leaf shed is unsightly and may reduce plant vigor during the current season.
What Can Be Done Control & Prevent Cercospora Leaf Spot on Crape Myrtle?
In the landscape, there are several things you can do to prevent or slow the development and spread of Cercospora leaf spot:
- If possible, avoid splashing of water on leaves by watering around the base of your crape myrtle. Also, when watering provide only enough water to keep the soil around the roots moist but not constantly soggy or wet, which can lead to other harmful plant diseases such as root rot. Rather than splash a little water around plants every day it's best to deep soak less frequently, allowing soil to dry somewhat between watering.
- Remove dead or heavily spotted leaves and discard them.
- Apply a slow-release shrub and tree type fertilizer to maintain a moderate growth rate. That said, cease fertilization two months prior to the average first-frost date in your area.
- Since the appearance of symptoms doesn't occur until mid to late summer, protective fungicide sprays are rarely needed for the control of this disease. That said, on plants that suffer noticeable damage every year, treatment with a copper-based fungicide can be helpful. Begin treatment in late spring or early summer if and when symptoms appear. Refer to the product label for mixing and application instructions.
Hope this information was helpful.
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