Fungal infections may cause brown leaves on ornamental trees or shrubs.
Crape myrtle was first introduced to the United States from China in the mid-1700s. Its showy flowers, attractive fall foliage and lush canopy make it an excellent ornamental shrub or tree for a home garden. One of the most common diseases of crape myrtle is cercospora leaf spot. If your crape myrtle is getting brown leaves, this fungus could be the problem.
Symptoms
In its early stages, cercospora leaf spot causes circular or irregular brown spots on leaves. Eventually the spots will enlarge, and on some cultivars they will turn from brown to yellow or bright red. Leaves infected with the fungus may become distorted before prematurely dropping off the plant. Typically, spots start to form on lower leaves near the base of branches and will spread upward and outward through the canopy until all the leaves are gone except for new growth at branch tips.
Disease Spread
The cercospora fungus is found in both nurseries and landscapes. Diseased cuttings are most likely the source of the fungus in home gardens and other landscapes. Spores overwinter on fallen leaves of infected crape myrtles and are spread by wind in the spring, re-infecting the same tree. In late summer, spore formation speeds up, and this is when you'll see the fungus spread from lower limbs up through the rest of the tree. Frequent rain showers and heavy dews can also facilitate the spread of cercospora leaf spot.
Cultural Control
If cercospora leaf spot is a persistent problem, you may want to consider removing your infected crape myrtle and replacing it with a resistant variety like "Fantasy" or "Carolina Beauty." At the end of the summer, collect and destroy all fallen leaves and twigs, as they may harbor overwintering fungus. You may need to thin out plantings around your crape myrtle; overcrowding reduces air flow and can facilitate the spread of the fungus. Frequent applications of low-rate nitrogen fertilizer, as opposed to one large application, can also help avoid cercospora leaf spot.
Chemical Control
Properly timed fungicide applications can be helpful for susceptible cultivars. Make the first application as soon as leaf spots begin to form on the lower leaves, usually in early to mid-July. Depending on the fungicide you choose to use, make followup applications at either one- or two-week intervals until September. Always read manufacturer's labels carefully.
Tags: cercospora leaf, cercospora leaf spot, leaf spot, brown leaves, crape myrtle