Azaleas prefer cool, humid climates and require humus-rich, loose, moist and acidic soils with a pH between 5.5 and 5.6. There is a certain requirement for light, but it does not tolerate exposure, and the leaves burn easily and die under the hot sun. The optimal growth temperature is 15°C to 20°C, and the growth tends to stagnate if the temperature exceeds 30°C or falls below 5°C. In order to better grow azaleas in the north, we now discuss the common diseases of rhododendrons based on our experience and habits over the years: Physiological diseases Moisture disorders Because the roots of azaleas are shallow rooted and delicate, they are afraid of drought and fear. Hey, improper watering, when fallen leaves, heavy, then died, so watering is a key to raising azaleas. 1. The soil is kept moist for the degree of water in the upper soil, the lack of oxygen in the root causes an anaerobic call, so that the accumulation of ethanol will lead to black root rot and necrosis. 2. The lack of water in the soil for a long time leads to the disappearance of the contraction of the plant cells, drooping of the shoots, which in turn affect the growth of the flowers, until the leaves wither, destroy the circulation, and cause death in severe cases. 3. Rhododendrons are light and slender, and have poor sucking ability. Fertilization is too thick or the dilution of chemical fertilizers is not enough. When the concentration of fertilizer solution exceeds the concentration of cell fluid in the root, the water in the plant body reversely infiltrates into the soil and causes loss. water. The main measures for preventing and controlling water imbalance are: Watering in spring, summer and autumn, potting and irrigating, and watering in 2 to 3 days, but it should be checked once a day and proper water supply should be provided. In the winter, water is less in the room until the pot is dry and then watered. Fertilization should adhere to the principle of “thin-fat and diligent applicationâ€. Do not apply too thick fertilizer, and do not mix manure, apply thin liquid fertilizer, and must be fully decomposed before use. The lack of nutrients causes a lack of nutrition in rhododendron plants, such as water imbalance, lack of light or burns, poor soil nutrients, alkali salt containing Glauber's salt or gradual alkalization, and so on. Another example is the lack of some trace elements in the soil, such as copper, sulfur, iron, manganese and other elements lack, the plants are all chlorotic chlorosis, known as the lack of disease. Symptoms and solutions can be found in the paper. There are roughly three stages of fertilization. That is, before the spring flower application long bud fertilizer, post-flower fertilization and differentiation of fertilizer; Shichang Lei fertilizer is mainly to promote flower bud differentiation, phosphate fertilizer should be the main. Chang Lei Fei Chunyu applied 1 or 2 times before March. Xia Xi should be applied before and after April. It must not apply more nitrogen. Otherwise, it will cause the branches and leaves to become long and cause the buds to shrink or drop buds. After the azaleas have been given flowers, they should immediately remove the stray flowers to avoid their sturdiness, and timely apply nitrogen fertilizer-based fertilizers 2 to 3 times, and apply them once every other week to promote the growth of new shoots, lush foliage, and compensation. Nutrients consumed by the plants at flowering. In order to prevent yellowing of azalea leaves, ferric sulphate + citric acid + water (1:1:100) should be added. Fertilizers are applied for 2 to 3 consecutive times; or 0.03% sulphur can turn yellow leaves green. Under normal circumstances, topdressing once a month, deciduous azalea into the greenhouse, the dormant period can not fertilize, and evergreen azalea once a month as usual fertilization. The amount of fertilizer depends on the growth potential of the plant and the size of the plant. Generally speaking, the plant is large and robust, and can be diluted with 2 to 3 parts of fertilizer and 7 to 8 parts of water. If the plants are small, then the concentration of fertilizer solution should be lighter, the ratio of fertilizer to water is 1:9. As for poor growth, it should be even lighter, or even not fertilized. The following diseases are only a few of them. Although the diseases caused by germs are different, the prevention and control methods are basically the same. Except for long-term ventilation, the common agents are as follows: 1. Root diseases. Roots that are caused by parasites of various bacteria rot or grow into tumors. Root rot and rhizotomy are common. For example, root nodule disease: damage to the roots of diseased plants, causing growth and decline in the aboveground parts, leaf atrophy and dryness. After brown spots, soft rot and other symptoms appeared on the roots, they were rotted and peeled. The xylem was blackish brown. After drying, sometimes darker brownish granular material appeared, which was the sclerotium of the pathogen. Medications are usually sprayed with 70% thiophanate-methyl or 50% carbendazim at the onset of the disease, and are also treated with 20% methyl-tocopherol 300 to 500 times. 2. Branch diseases. Common stem rot, ulcer disease and so on. Symptoms are branches rot, epidermis dehiscence, dendritic lipids, branches, spots, stains, and tumors. 3. Control methods: A. Lime sulfur agent. A red-brown, transparent liquid tanned with lime, sulfur, and water (1:2:10) for about 50 minutes. The Baume degree is 27 to 28 degrees. Mixing water makes Baume degrees 5 degrees. Spraying before the spring can prevent a variety of diseases. B. Spray polyhydrazine sulphide (70%) 400 times. C. Carbendazim. Generally use 50% wettable powder 1∶250 and 1∶500 two kinds of solutions, with the protection and treatment of plants. 3. Mosaic disease. Common leaf spot, yellowing, leafy swollen disease and so on. The agents used are: A. Bordeaux mixture (1:1:200). The sky blue liquid formulated with copper sulfate and lime milk is alkaline. Can prevent diseases caused by a variety of germs. B. 80% M-45 wet powder 600 times, spray once every 10 days. C. 70% Antai WP 600 times, spray once every 7 days. Du Fu deficiency symptoms and solutions: Rhododendrons lack of nitrogen, plants from the lower yellow from the green, veins light red. Treatment measures: topdressing urea 0.2 ~ 0.5 (application concentration %); Rhododendrons lack of phosphorus, the old leaves were dark green, stems and veins become purple, appear necrotic area. Treatment measures: top-dressing of potassium Dihydrogen Phosphate 0.2~0.5 (application concentration %); Rhododendron lack of potassium, mottled green areas of leaves, leaf margins and tip of the leaves produce necrosis area. Treatment measures: topdressing of potassium dihydrogen phosphate 0.2~0.5 outside the root (application concentration %); Rhododendron iron deficiency, from the young leaves and the growth of the top of the yellow, the edges of the leaves become brown and dead. Treatment measures: external root dressing, spraying and watering at the same time, ferrous sulfate 0.02 ~ 0.05 (application concentration%); Azalea sulfur, young leaves began to lose green, but not wither, the leaves edge brown dead. Treatment measures: The root topdressing ferrous sulfate 0.02 ~ 0.05 (application concentration%); Copper deficiency in the azaleas, the young leaves and the growth of the top began to lose green, young leaves withered. Treatment measures: Copper sulfate outside the root 0.02 ~ 0.05 (application concentration%); Rhododendron lack of manganese, necrotic lesions between young leaves began to occur, the young leaves do not wither. Treatment measures: Apply manganese sulfate 0.05~1 (application concentration %) outside the root;
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