What are the common diseases of rhododendron? How to prevent and cure?

The main diseases of rhododendron are root rot, brown spot, black spot, leaf blight, iron deficiency chlorosis and so on.

After the rhododendron suffered from root arm disease, the growth was weak, the leaves wilted and withered, the surface of the root system appeared water-stained brown fields, serious soft rot, gradually rotted and peeled, and the xylem blackened. The disease is most likely to occur in an environment with high temperature and high humidity.

The prevention and control method is to strictly disinfect Pei 10 soil before turning the basin, and keep the soil condition sulfur loose, moist, make it have good permeability, and avoid stagnant water. If the plant is found to be sick, the diseased plant and basin soil should be dealt with in time. During treatment, the diseased plant can be eluted with 0.1% potassium permanganate aqueous solution or 2% ferrous sulfate, then rinsed with clean water and put on the basin again. The basin soil can be cured by spraying basin soil with a solution of 70% topzine wettable powder and 1000 times water.

Brown spot is a major disease of rhododendron. At the beginning of the disease, small brown spots appeared on the leaf surface, which gradually developed into irregular spots, and many black or grayish brown spots were produced on the disease spots, which made the damaged leaves yellow and fall off, affecting the flowering of the current year and the development of flower buds in the coming year. This disease often occurs during the rainy season when the humidity is high.

The treatment method is to pay attention to make the plant ventilated and transparent, not to make the humidity too high, and to increase the application of organic fertilizer and nitrogen, phosphorus and potassium mixed fertilizer to enhance the plant resistance to infection and growth. If diseased leaves are found, they should be removed in time and burned centrally. At the initial stage of the disease, 0.5% Bordeaux solution or 0.4 Baume stone sulfur agent was sprayed, and 4% flour was added to increase the adhesion. Leaf spot and black spot can also be treated with the same method.

Iron deficiency chlorosis often occurs in alkaline soil areas, when the disease is mild, only the plant late green phenomenon; in severe cases, the leaf tissue can all turn yellow and the leaf edge scorched. When the disease occurs, it is most obvious in the leaves of the top tip of the plant, which is generally caused by internal iron deficiency.

The control method is to change the property of iron deficiency in soil and reduce soil alkalinity. Apply more organic fertilizer to transform clayey soil. 0.2%-0.3% ferrous sulfate liquid can be directly sprayed on iron-deficient plants. You can also poke several holes about 15 cm deep in the soil around the plant with chopsticks and slowly inject them with liquid ferrous sulfate solution at 1:30 to fill the holes to increase soil acidity and reduce alkalinity.

The incidence and environmental conditions of rhododendron black spot are similar to those of brown spot, and similar methods can be used for prevention and control.