1. Zinc deficiency in citrus
In general, new mature leaves of the new leaves are yellowed, yellow-green to yellow, and the main and lateral veins and nearby mesophyll are still normal green.
The main and lateral veins of the old leaves have an irregular green band and the rest are pale green, yellowish or orange. Some leaves only show yellow and light yellow small blocks between the main green and side veins.
In the case of severe zinc deficiency, the diseased leaves were significantly erect and narrow, and the new shoots were shortened. The branches and leaves were clustered and then the branchlets died. However, the new shoots growing on the main branches or trunks were nearly normal.
Orange is most susceptible to disease, with small and thin fruit, smooth surface, pale yellow, wood pulp, juice less tasteless, Wenzhou oranges, local as early as broad-leaved citrus disease, fruit smaller, smoother skin thickening , poor coloring, small fleshy juice.
2. Causes of zinc deficiency in citrus
In the acidic (PH4.0-5.5) red and yellow loam soil, the effective zinc content is low, and it is easily lost. Especially in acidic sandy soil, it is easily lost, and zinc deficiency occurs easily.
In weakly acidic to alkaline (PH6.0-8.5) purple and salty alkaline soils, zinc salts often become insoluble and difficult to absorb and cause zinc deficiency.
In old orange gardens that have been planted for too long, the zinc contained in the soil is absorbed and depleted of zinc.
Excessive application of nitrogen fertilizers affects the absorption of zinc and reduces the content of zinc in leaves. Excessive application of phosphate fertilizers in soils with a pH above 5.5 results in the formation of insoluble phosphate fertilizers and the formation of insoluble zinc phosphates, all of which are likely to induce zinc deficiency.
The lack of organic matter in the soil makes it difficult for zinc salts to convert into effective zinc, exacerbating the occurrence of zinc deficiency.
The lack of trace elements such as magnesium and copper in the soil can lead to root rot, affect the absorption of zinc, and zinc deficiency can also occur.
In spring and summer, there is much rain, and the effective zinc is easily lost. The autumn drought reduces the effectiveness of zinc and is prone to zinc deficiency.
3. Treatment of citrus zinc deficiency
Soil fertilization manure, cake fertilizer, green manure and other organic fertilizers can effectively cure citrus zinc deficiency. The application of zinc sulfate in soil is better, but the dosage should be controlled to prevent phytotoxicity. The application amount per mu should not exceed 2 kg.
When foliar spraying of spring shoots is started, 0.1%~0.2% of zinc sulfate is sprayed once, usually 1-2 times a year, and severe trees can be sprayed again in early summer.
4. Citrus zinc excess disease
Symptoms: Leaves burn, deciduous shoots and other symptoms. Associated with iron deficiency chlorotic yellowing disease.
Control methods: When soil zinc is excessive, it is advisable to apply superphosphate in alkaline or calcareous soils with high soil pH. Lime is preferred for acidic soils with low pH. After application, it should be watered or irrigated to promote the dissolution of superphosphate or lime, accelerate the detoxification, and can rinse and dilute the role of zinc in the soil.
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