Western Rhododendron Disease Prevention and Control
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Western rhododendrons are more demanding on the environment, sour and wet, and afraid of the sun, they are not able to tolerate water, and are slightly careless, that is, abnormal growth and disease. Common diseases of Western azaleas include: brown spot, tip blight, blight, red leaf disease, and lobular disease. After the occurrence of these diseases, the light leaves were distorted and discolored, the flowers were small and dark, the flowering period was shortened, and the growth rate was slowed down; in serious cases, the whole plant withered and died, seriously affecting the ornamental effect. According to the observation and research in recent years, the common diseases of Rhododendron orientalis have certain symptom characteristics and incidence rules, and effective measures can be taken to prevent and treat it. First, brown spot 1. Identification characteristics: This disease is a kind of leaf disease that is more likely to occur in Rhododendron arundinacea. It can occur in almost all cultivated species and regions. The diseased leaf initially produces round spots of varying sizes on the surface and soon expands into round, elongated or irregular lesions, with a diameter of about 2 mm to 10 mm. The lesion is dark brown on the edge, and the middle is yellow-white or off-white. , Slightly uplift, the middle of the late lesions dry, the formation of circular holes, adjacent lesions can form irregular large spots, severe leaves dead, the central scattered small black spots. 2. Occurrence characteristics: Brown spot is a fungal disease, caused by the infection of leaf spot mold. The germs are mainly derived from the diseased bodies in the soil. Overwintering germs can produce propagules when the climatic conditions are appropriate, spread by airflow, and invade from plant stomata, lenticels, or wounds, and are widespread and severe at 25°C-28°C and high humidity conditions. In addition, soil moisture content, fertilizer is insufficient, plant growth is weak, it is easy to induce the disease. 3. Control measures: 1 Strengthen field management and enhance plant resistance to disease. Using sawdust that has been rotted or steam sterilized as the cultivation substrate can reduce the source of pathogenic bacteria, keep the soil moist, loose, breathable, and free of stagnant water, cultivate robust plants, and enhance disease resistance. 2 Clean the potted soil and remove the diseased leaves. In combination with topdressing, the diseased leaves are removed from the field or buried deep underground to reduce the source of the disease. 3 timely spraying or watering 800 times to 1000 times the ferrous sulfate solution, adjust the soil pH. 4 chemical control. The drug is protected at the beginning of the disease to prevent the spread of the disease. 70% thiophanate-methyl wettable powder 1000 times, or 80% mancozeb wettable powder 600 times liquid, sprayed 7 days to 10 days, 2 times to 3 times. Can also be used carbendazim or chlorothalonil and thiophanate-methyl alternately used to improve the efficacy of the drug, reducing the resistance of bacteria. Second, blight 1. Identifying characteristics: The disease mainly occurs in the rhododendron plants that have been transplanted soon or an annual. At the time of initial onset, an elliptic dark brown lesion developed on the base of the stem near the ground, and the disease progressed slowly. As the lesion progressed, the depression appeared. When the lesion circled the stem for one week, the stem base contracted and dried up. When the humidity is high, the diseased part often has light brown spider web-like hyphae, and sometimes it can form brown sclerotia with different sizes. 2. Occurrence characteristics: Blight is also a fungal disease, caused by Rhizoctonia infection. The pathogenic bacteria mainly threw up mycelia and sclerotia on the remnants of the diseased plants or in the soil. After the temperature rose again the following year, the disease began to occur when the soil moisture content was too high, the light was insufficient, and the plant growth was thin and weak. If the watering is too much or the rainwater is not drained in time, the cultivation matrix will be too stuffy; or the doors and windows will not open in time, so that the earth temperature of the seedbed will change too much; or the insulation will be poor, which will cause the soil in the bed to easily induce the disease. 3. Control measures: 1 Cultivation substrate preparation. For potted plants, 2/3 of the sawdust and 1/3 of pebbles with good water absorption and drainage capacity should be selected as the matrix. Sterilization and sterilization should be performed before cutting and organic fertilizer should be applied to enhance fertility. 2 seedling management. The most important is the control of temperature and humidity. At low temperature, attention should be paid to the insulation in the shed to avoid freezing. When the humidity is high, it is necessary to pay attention to ground ventilation. During the day, in the case of seedlings not affected by freezing, ventilation and air ventilation should be as much as possible. 3 drug control. Planting the cutting substrate before cultivation requires chemical treatment, and 50% of carbendazim wettable powder can be used. The dosage is 8g-10g per square meter. At the beginning of the disease, 75% chlorothalonil WP can be sprayed 600 times or 64% poisonous WP can be used 500 times, 7 days to 10 days, usually 2 times to 3 times. Since spraying the liquid will cause the humidity in the bed to be too large, it is necessary to ventilate and reduce the humidity in the field. Third, tip blight 1. Identification characteristics: The disease occurs on both annual and perennial Western rhododendrons, and starts from the upper leaves or young leaves. The tips of the upper leaves turn green and yellowish-white at the tip of the leaf, and the gradient is brown and extends toward the base of the leaf. The two sides of the edge of the rewinding, the lesion length of about 2 mm to 14 mm, accounting for about 2/5 of the total length of the diseased leaf. Disease and health at the junction clearly, leaves and branches dehydration wilting. The stalks of the diseased leaves and the stalks near the diseased leaves may turn brown or dark brown in the middle, and the severe strains often wilted and die. 2. Characteristics of the disease: The disease is also caused by a fungal infestation. Under appropriate conditions, the bacteria invade from the stomata or wounds of the leaf tip, spread from the invading point into the vascular bundle tissue in the plant body, and transport the water and nutrients in the plant body. Expanding to other sites, if the bacteria spread to one side of the vascular bundle, it will show half of the plant withered and half normal. 3. Control measures: with brown spot. It is also possible to use slow-release fertilizers to reduce the number of foliar sprays and prevent germs from spreading during the water spray process. In addition, the soil is disinfected with Dixon before cuttings. After onset of cuttings, potted azaleas can be changed for pots and soils; if the disease occurs before the end of March to early April, carbendazim and thiophanate-methyl may be sprayed alternately. Fourth, red leaf disease 1. Identification characteristics: Red leaf disease is a physiological disease. At the early stage of disease, the leaf mesophyll tissue of the leaf appears dark red dots, and soon the red patch expands, the color deepens, and the veins remain green. Subsequently, the lesions turned brown and increased in size. Finally, the red, brown, and green patches of the entire leaf gradually dried out and fell off. If the drug is used at the beginning of the disease, red and brown patches can gradually disappear. If the drug is used in the middle and later stages, the symptoms cannot be eliminated, but the newly regenerated heart is green and normal. 2. Cause of disease: Red leaf disease is mainly caused by magnesium deficiency. Magnesium is an important element in the life activities of plants. If there is a deficiency of magnesium, chlorophyll cannot be formed and the photosynthetic efficiency decreases. Second, the activity of multiple enzymes in the respiratory chain is weakened, the respiration is hindered, and the energy is reduced, which seriously affects the mineral metabolism of plants. The third is the weakening of nitrogen metabolism, the reduction of synthetic amino acids, resulting in excess carbohydrates, excess carbohydrates forming more anthocyanins, red leaves, thin plants, and aggravating the occurrence of other diseases. 3. Prevention and control measures: The focus of prevention and control of red leaf disease is to cultivate robust plants, increase disease resistance, increase light, promote photosynthesis and mineral metabolism, and pay attention to the application of complete fertilizer, such as cake-flooded cake fertilizer water diluted 5 times to 10 Watering times, acupuncture dry cattle manure (not only can increase temperature and increase fertilizer, but also can keep the soil loose), the other at the beginning of the disease with 1500 times -2000 times magnesium sulfate solution spray 2 to 3 times, the effect is very good. V. Leaflet disease 1. Identification characteristics: Lobular Bing is also a physiological disease, its symptoms are as follows: the top of the branches are shortened between the nodes, the leaves are clustered, the new leaves are obviously smaller, about 1/3 to 1/2 of the normal leaves, and the leaves are darker. Slow growth. 2. Causes of etiology and prevention of lobular disease are mainly caused by zinc deficiency. In the absence of zinc, indole acetic acid and serine in the plant cannot be synthesized into tryptophan, and thus no auxin can be formed. In the absence of auxin, growth site is first suppressed. The cells divide and elongate, so they must lead to shortening of the internodes and clustering of leaves. In the prevention and control can be sprayed 800 times to 1000 times the zinc sulfate solution or mixed with 1% urea, every 7 days to 10 days 1 consecutive 2 or 3 times. Another cultivator can loosen soil, improve soil ventilation, enhance root activity, and promote the absorption of nutrients.