Brown spot is a common issue during the growing season of crape myrtle plants. When the disease becomes severe, it causes an excessive number of yellowing leaves and premature leaf drop, which significantly reduces the plant's ornamental value and flowering potential.
The pathogen responsible for Lagerstroemia brown spot is a fungus that primarily affects the leaves. The infection usually starts on the lower leaves and gradually moves upward. In the early stages, the lesions appear as irregularly shaped, round or nearly circular spots, ranging in color from purple-black to black, with lighter margins. As the disease progresses, the lesions darken, and the boundary between infected and healthy tissue becomes more distinct. A grayish or black mold may develop on the center of the lesions. In advanced cases, the spots merge, causing the entire leaf to turn yellow and fall off quickly.
The disease is caused by the fungal pathogen *Cercospora littoralis*. The pathogen overwinters on infected plant debris in the form of mycelium or conidia. In the following growing season, the conidia are the main source of initial infection and reinfection. These spores are easily spread by wind, rain, or air currents. The disease tends to occur more frequently during hot and rainy periods, especially when storms are common. Lower leaves are generally more vulnerable than upper ones.
To manage Lagerstroemia brown spot, early detection and cultural control are essential. Infected branches and leaves should be removed promptly and either burned or buried to reduce the inoculum. Proper pruning helps improve air circulation and light penetration, which can help prevent disease development.
In the early stages of infection, fungicides such as 50% carbendazim wettable powder diluted at 500 times, 65% dexamethasone wettable powder at 1000 times, or 75% chlorothalonil wettable powder at 800 times can be applied to control the spread of the disease. Regular monitoring and timely intervention are key to effective management.
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