Why are there white spots on the leaves of the rhododendron?

There may be several reasons: 1. Insect pests: spider mites, also known as red spider mites. Spider mites are small, red and difficult to see with the naked eye. It likes to suck sap from the underside of leaves. The infected leaves will turn yellow with many small white spots appearing, and will soon wither and fall off. Spider mites have a strong reproductive capacity and can produce more than 10 generations a year. They often breed in high temperature and low humidity environments.

Control methods: Remove weeds in the pot and eliminate overwintering eggs. When causing damage, use 1,000-1,500 times of dimethoate emulsion containing 40% dimethoate (i.e. add 1 to 1.5 grams of dimethoate to 1 kilogram of water), or spray scale insects with 2,000 times of dimethoate emulsion containing 40% dicofol. Like blood lice, they suck the sap of plants, thus causing great harm to flowers and trees. Not only do the affected plants have poor growth, but their leaves will turn yellow and fall prematurely. In severe cases, the plants will wither and die. During the process of cultivating flowers, if scale insects are found on individual branches or leaves, you can gently brush them off with a soft brush, or combine them with pruning to remove insect branches and leaves. It is required to brush, cut, and burn them together, and do not throw them away.

2. Disease: Powdery mildew

Symptoms: Powdery mildew is a fungal disease, which is a common disease on flower plants. It mainly occurs on plant leaves and can cause infection in severe cases. The most prominent feature of the plant's young leaves, young buds, young shoots and flower buds is that a layer of powdery substance appears on the back or both sides of the leaves during the disease. In the early stages of the disease, nearly round or irregular white powdery spots appear on the infected parts. And slightly chlorotic or deformed. Under suitable conditions, the powdery spots expand rapidly and connect into sheets, leaving the leaves covered with white powdery mildew. In the later stages of the disease, the diseased leaves will appear wrinkled and uneven, curling back, and the flowering period will be significantly shortened or the flower buds will not expand normally. In severe cases, the plants will be dwarfed, the flowers will be few and small, the leaves will shrink and dry up, and even the entire plant will die. Cut off diseased branches, diseased buds, and diseased leaves in a timely manner, and clean up rotten branches and leaves in the garden to reduce the source of infection; strengthen cultivation management, and avoid excessive planting density and potted flower placement; pay attention to ventilation and light transmission; apply more phosphorus and potassium fertilizers , an appropriate amount of nitrogen fertilizer should be used; chemicals such as thiophanate and carbendazim can be sprayed.