Woolly Rhododendron Pest and Disease Control Methods and Key Technical Points

I. Brown Spot Disease

This disease may cause the woolly rhododendron to drop its leaves prematurely and to wilt and turn yellow, thereby reducing its ornamental value and worth. The disease starts from the lowest part of the plant and then affects the leaves. In the early stage of infection, numerous reddish-brown spots appear, which then evolve into a more rounded shape, and finally turn into dark brown angular spots. It generally occurs mostly in April and May, and symptoms only begin to decrease in December. However, if rhododendrons are grown at warm room temperatures, the disease may occur throughout the year. This disease is especially severe during the rainy season; after rain stops, as long as some water remains on the leaves when night falls, the disease may be triggered. In artificial cultivation, plants with stronger resistance can be selected for growing as far as possible, or in winter and spring, care should be taken to promptly clear standing water and diseased leaves.

II. Chlorosis

The main cause of this disease is a lack of iron in the woolly rhododendron, and it is also a common disease of rhododendrons. When the plant develops this symptom, its leaves turn white and thin, and then as the condition gradually worsens, the leaves may turn yellow or die. If we want to prevent and control this disease, we need from the very beginning to choose acidic soil with mountain soil as the growing medium for planting. When watering, we need to avoid using water that is too alkaline, and it is best to use normal rainwater. If infection occurs accidentally, we can irrigate it with black alum water, using it again each time the leaves become wrinkled, repeating this cycle until it returns to normal.

III. Stem Base Rot

The main cause of this disease is that during the seedling stage, the growing medium repeatedly used by workers later produced pathogenic bacteria, or because the pH value of the medium was too high, or because wounds were produced when transplanting the rhododendron and were not sterilized in time. This then affects the plant's growth and development, causing its leaves to drop. The way to prevent this disease is to first disinfect the medium to be used before transplanting the rhododendron and adjust its pH to about 5.0, and during transplanting take care not to let pathogens invade through its wounds.