Rhododendron yellowing disease is a physiological disease, but the formation of yellowing disease is complicated. If prevention and control of the disease are often futile, it must be carefully observed to determine the disease condition, identify the cause of the disease, and then treat the disease. The various symptoms, etiology, and effective control measures for rhododendrons are described as follows: 1. Iron deficiency. 1. Iron deficiency in soil: The formation of chlorophyll requires iron and nitrogen and other elements. The phenomenon of yellowing caused by iron deficiency in the soil often occurs. Therefore, it is very important to supplement the iron elements in the soil. Ferrous sulphate powder can be evenly distributed into the basin. Soil surface, 1.5 centimeters in diameter can be used 1.5 grams of pots, and so on, and then sprayed with water to dissolve the water, soluble in water can also be watered, the concentration of 1%, or add zinc sulfate, borax, etc. can also be restored until recovery. Plants with thicker trunks can also be slowly injected into the trunk with 0.75% ferrous sulfate for control. 2. When the pH of the soil or soil is slightly alkaline, the pH of the soil will affect the absorption of nitrogen and iron in the roots. The leaves will gradually yellow off from the bottom. The vinegar should be used to neutralize the alkalinity of the water to reduce the pH value. Between 5 and 6 rooms, water again. The soil can be used to modify or replace the pots and earths as described in Items 1 and 2. In serious cases, 0.3% citric acid can be added to the ferrous sulfate solution, stir and apply to increase the long-lasting effect of adhesion. Second, choose a good soil. It is advisable to use loose, well-drained, acidic sandy loam rich in humus, which can be selected from 7 parts of humus, 2 parts of garden soil, 1 part of sand, mixed preparation, and a small amount (about 50 grams per pot) of hemp sauce residue. Bone meal, etc., is used as cultivated soil; avoid the use of calcareous alkaline earth or poorly drained clay soil; in the course of cultivation and management, it is necessary to dry without cracking, tide and not wet, in order to promote the germination of new roots. Third, pay attention to prevent fertilizer. The rhizome is fine and silky. It responds extremely sensitively to fertilizer concentrations. If it is too strong, yellowing, shedding, or even death may occur. Especially once yellowing disease occurs, fertilization should be stopped immediately; fertilization outside the roots has a certain role, but it does not solve fundamentals. The problem is to be stabilized for a period of time. After the lignification of the new green branches is completed, fertilization can be carried out. Otherwise, it is still possible to yellow again. Fourth, to be willing to remove buds. Plants suffering from yellowing disease, even if the flower buds are ripe to open flowers, but due to flowering to consume a large number of nutrients, affect disease recovery, it should be as early as possible regardless of the size of all buds, are removed. Fifth, light must be suitable. The formation of chlorophyll requires light, and only sufficient sunlight can make the leaves appear normal green. Insufficient light will yellow the leaves. However, the roots of the diseased plants are weak and the leaves are easy to wilt under strong light. Therefore, the summer and autumn light must be shaded during the high temperature season, and the light should be increased in late autumn and winter and spring to restore the diseased plants. In short, once the rhododendron has yellowing disease, it should patiently improve the curing conditions, symptomatic use of the above-mentioned effective prevention and treatment measures, preparation for half a year to a year or so, intensive care, can make the disease plant reproduce vitality.
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