How to prevent and cure the disease caused by "hunger" of growing citrus

Zinc deficiency causes leaf spot disease. Citrus leaf spot disease is a common disease, and the typical symptom is mottled leaflet. At the beginning of the green stage of the new leaves, the main veins and lateral veins were significantly green, and the rest of the tissues were light green to yellowish white and shiny. In severe cases, only the main veins or thick lateral veins are green, and the new leaves are narrow, mottled and erect, short internodes and clumps. Mottling is caused by zinc deficiency. Zinc deficiency in a variety of soils, such as granite, gneiss and serpentine, the soil formed by granite, gneiss and serpentine contains less zinc; acidic sandy soil is easy to lose zinc; alkaline soil zinc is easy to form insoluble compounds, so zinc deficiency. In addition, the soil is too dry and wet, too little humus or too much organic matter, which hinders the contact between the root system and the soil, and heavy shearing is prone to zinc deficiency. Foliar fertilization has a good effect on the prevention and treatment of zinc deficiency. It is appropriate to spray 0.2%-0.3% zinc sulfate (with the same amount of lime) solution at the tender shoot stage, and spray 2 times for severe zinc deficiency.

Shoot blight caused by copper deficiency or boron deficiency. At the initial stage of copper deficiency, the new shoots of citrus are long, soft, slightly curved, the leaves are large and dark, and the results are few, so it is easy to be mistaken for overgrowth. In severe cases, the tip of the branch becomes tea-brown and dies, short and weak clumps occur, and it is easy to dry up and fall early and glue. When the branch is ripe, the wound is reddish brown, and the leaf part is reddish brown. Citrus needs very little copper, so it is enough to spray Bordeaux solution. However, copper deficiency is easy to occur in peat soil, acid sand, soil with high content of organic matter, grazing and grazing sites, excessive application of barnyard manure and phosphate fertilizer, and copper deficiency in newly reclaimed orange orchards without Bordeaux solution for several years. Boron deficiency of citrus: the growing point of the bud died continuously and formed clusters of buds, the veins of the leaves were swollen, corked or broken, the fruit was small and deformed, the skin was thick and hard, and there were brown resin deposits in the core and sponge layer. Boron in acid soil is easy to be lost, so it is lack of greenhouse. The boron content of soil parent materials such as granite, gneiss and schist is very low, while the solubility of alkaline soil is poor and boron is also deficient. Excessive application of phosphate fertilizer or lime, or soil drought, affect the availability of boron and the absorption of boron by roots. Limes have weak boron absorption, so citrus rootstocks are generally boron deficient. For copper deficiency, Bordeaux solution or other copper fertilizer can be sprayed. Boron supplement can be fertilized in soil, or 0.05%-0.1% boron fertilizer solution can be sprayed at budding stage, flowering stage and small fruit stage.