What are the control methods of Lagerstroemia indica leaf spot?

Potted Lagerstroemia indica starts from the lower old leaves in summer, and the upper epidermis of the leaves decays like water stains, and develops inward from the edge. Spraying chlorothalonil is ineffective, and it should be a combined disease of rust and leaf spot in the early stage.

Prevention and control methods: ① Strengthening ventilation and lighting, controlling the humidity of basin soil, applying organic fertilizer on time, removing diseased leaves and burning can reduce the chance of disease. (2) spraying 50% triamcinolone acetonide wettable powder, adding 1800 ~ 2000 times of 25% triamcinolone acetonide wettable powder, mixing and spraying; Or 600 times of 75% chlorothalonil wettable powder and 800 times of 65% zineb wettable powder. Both should be given once every 7 days, 3 ~ 4 times in a row, which can inhibit the development of the disease.