Friends who have raised rhododendrons know that rhododendrons are very difficult plants and flowers to raise. In addition to the slightly higher requirements of the growing environment, pests and diseases are also the main factors leading to the failure of aquaculture. Below I have compiled some knowledge about rhododendron diseases and pests, I hope it will be helpful to you who like to raise flowers.
disease control:
Root rot
Rhododendron suffers from root rot and growth is blocked, the leaves are wilted, dry, water-stained brown patches appear on the surface of the root system, severe gradual decay and peeling, and the woody part slowly turns black. This disease is prone to occur in environments with high temperatures and high humidity.
Prevention and control methods: Strictly disinfect the soil before turning over the pot, and keep the soil loose, fertile, and make it permeable to avoid standing water. If a plant is found to be sick, the diseased plant and potting soil should be treated in time. During treatment, the diseased plant can be washed with 0.1% aqueous potassium permanganate or 2% ferrous sulfate, and then rinsed with water and re-potted. Spray the potting soil with a solution made of 70% tolbuzin wettable powder plus 1000 times water.
Brown spot disease
When rhododendron brown spot disease first occurs, small brown spots appear on the leaf surface, and gradually develop into irregular large spots, and many black or gray-brown dots are produced on the spots, which make the affected leaves yellow and fall off, affecting the flowering of the year and the development of buds in the following year. This disease often occurs during the rainy season and is caused by excessive humidity.
Control methods: Transfer the plants to a ventilated and ventilated environment with astigmatism, and increase the application of organic fertilizers and mixed fertilizers of nitrogen, phosphorus and potassium to enhance the resistance of plants to infection and growth ability (fertilization should not be too thick, thin fertilizer should be applied diligently). If the diseased leaves are found, they should be removed in time and burned in a concentrated manner. At the beginning of the disease, spray 0. 5% Bordeaux liquid or 0. 4 Baumedo stone sulfur compound, and add 4% flour to increase adhesion. Leaf spot disease and black spot disease can also be treated in the same way.
Yellowing disease
Iron deficiency yellowing disease often occurs in the northern region of the soil with alkaline soil, and when the disease is mild, the plant will appear late greening; in severe cases, the leaves can all turn yellow and the leaf edges are scorched. At the onset of the disease, it is most pronounced on the leaves of the plant's apex, which is usually caused by the lack of iron in the plant.
Control method: Improve the iron properties in the soil in time and reduce the alkalinity of the soil. Increase the application of organic fertilizer to improve the soil. It is also possible to spray O. 2% to 0. 3% liquid ferrous sulfate. In addition, you can also poke several holes about 15 cm deep with chopsticks on the soil around the plant, and slowly inject it with a 1:30 aqueous solution of ferrous sulfate to fill the holes to improve the acidity and alkalinity of the soil.
Pest control:
Military worms
Adult insects are small and flat, about 4 mm long, black, is the most harmful pest to the evergreen rhododendron, often in the back of the leaf sucking leaf liquid as a pest, the damage to the leaf surface appears yellow-white spots, so that the leaves fall off, causing the tree to weaken, affecting growth and flowering.
Prevention and control methods: mainly spraying with drugs. It can be sprayed with 90% dichlorvos original drug 1000 times liquid or 40% oxidized Lego emulsion 1500 times liquid or 50% borer pine emulsion 1000-1500 times liquid spray control.
aphids
It mainly harms the young branches and leaves of rhododendron, the light can make the leaves lose green, and the heavy ones make the leaves shrink, become hard and brittle, and cannot absorb nutrients, affecting growth.
Control methods: Usually pay attention to the aphids during the wintering period, after wintering, you can spray a 5-degree stone sulfur compound on the plant to eliminate the overwintering insect eggs, shovel the weeds near the flowers, and eliminate the source of insects. During the aphid infestation period, it is sprayed continuously with a solution made of 40% or oxidized fruit plus 1200 times water, and the effect can be seen 3-4 times.
Short beard
Short-bearded is one of the common pests of rhododendron, often sucking sap near the main vein on the back of the leaf, causing many patches to form on the back of the leaf, and finally causing the leaf to fall off. This worm is inverted ovate and has a body length of about 0. 3 mm, flat body, body color is red, dark red, wood red, the back of the body has irregular black spots. The insects are most common in summer when they are hot and dry, and decrease when there is a lot of rainfall.
Control methods: In mid-to-late October and early spring in March, each spray of 25% insecticidal water expanding agent 500 times liquid can be controlled by spraying a Baume 0.5 degree stone sulfur compound.