The symptoms of black rot are common on the leaves. There are many small purple brown wet spots on the damaged leaves. There are irregular spots on the lower surface of the leaves, and then the spots gradually spread. The diameter of diseased spots can reach 3cm, some can even reach 7cm-8cm, the larger diseased spots will turn black brown or black, and water will exude when pressed hard, while the old diseased spots will turn dry black; then the leaves will become soft and black, soon become rotten, which will cause the whole leaves to turn black and die.
The pathogens live through the winter in mycelium and sporopollen disc in the remains of the diseased parts. They are transmitted by rain sputtering, rolling and infecting, and polluted planting materials and running water. The disease starts from 20 ℃ to 25 ℃, and the disease onset period is from June to September every year. It can be repeatedly infected. When the temperature is 25-28 ℃, the disease spreads rapidly, and the pathogen spreads rapidly, causing serious damage. From August to October, the incidence was more in southern China. Generally, the disease can be induced by basin soil hardening, too dense planting, poor air circulation, poor management of fertilizer and water, excessive application of nitrogen fertilizer or water sprinkling at the head. Especially at the turn of summer and autumn, when the rainfall frequency is more and the rainstorm and autumn rain are continuous, the disease is more serious.
Remove dead leaves and diseased bodies, and cut off the diseased segments.
To improve the permeability of the garden, the basin soil should be slightly acidic, and the basin soil should be fertile. The pond mud, bark and other plant materials should be used for cultivation, to increase fertilizer, pay attention to shade and avoid watering.
Protect new leaves by spraying, spray chemical agents to eliminate diseases, keep ventilation and avoid wetness.
