1. 1 Soil acidification and hardening are serious.

Soil acidification in southern China is quite serious, on the one hand, it is caused by acid rain under the influence of weather, on the other hand, it is caused by long-term single use of chemical fertilizer. The pH value of soil is between 3 and 5, which is not conducive to the growth and reproduction of beneficial bacteria. When the activity of beneficial bacteria in soil decreases, it will cause soil hardening and poor ventilation, which will make the root system in sugar orange unable to grow and renew normally, leading to root system aging and yellow tree body.

1.2 Soil organic matter content is insufficient.

The content of soil organic matter in southern China is mostly below 1%. Only when the content is about 3%, crops can grow and develop normally. Organic matter can not only provide carbon and other nutrients for plants, but also provide a place for biological bacteria to survive and reproduce, and improve our soil water and fertilizer conservation ability. Some farmers only applied chemical fertilizer 2-3 times in 1a, but did not apply organic fertilizer. Therefore, if there is no reasonable and sufficient nutrient supply in the sugar orange, the slow-growing trees will become weak and yellow.

Trace elements in 1.3 are insufficient.

Most farmers only pay attention to the application of nitrogen, phosphorus and potassium, and do not supplement medium and trace elements. Sugar oranges will turn yellow due to the lack of magnesium, zinc and iron. The symptom of magnesium deficiency in sugar orange is that the mesophyll of old leaves begins to appear mottled yellowing, and the main vein and leaf bottom remain green, forming an inverted V-shaped yellowing; Iron deficiency is mostly manifested in new leaves, which are normal in size, but the whole new leaves are yellow-green; The symptoms of zinc deficiency are also manifested in the new leaves, which turn yellow evenly and the severe leaves become slender. The lack of elements is sometimes caused by the lack of multiple elements at the same time, especially in orchards that have just started production. Every year, fruit trees will take away a lot of medium and trace elements when they bloom and set fruit. Once the fruit trees are short of boron and magnesium fertilizer, they can't blossom and set fruit normally. Even if the hormone is used to keep fresh, the fruit will be rough and dull, and the taste is not good, so it can't sell at a good price. If the medium and trace elements are not supplemented in time, the fruit trees will soon turn yellow.

1.4 Yellow caused by poor drainage

Many farmers plant sugar oranges in rice fields to achieve premature delivery and high yield. Because paddy fields are mostly low-lying and high-water, and the drainage is not smooth, if it rains heavily continuously, the whole orchard will be soaked by water. In addition, sugar oranges are dryland crops. If the accumulated water is serious for a long time, it will make the roots retch and rot, causing the trees to turn yellow. After the rain, some farmers saw that the fruit trees were not growing well, thinking that they were short of fertilizer, so they bought some chemical fertilizers to apply. If improperly applied, it will accelerate root rot.

1.5 Bad healing of marriage interface leads to yellowing.

Because the sugar orange seedlings planted now are grafted seedlings, sometimes they turn yellow because of poor affinity, poor transportation of nutrients, or poor transportation caused by dislocation of the cambium during grafting.

1.6 nematodes cause yellowing.

Rhizobia absorbed all the nutrients in the root system of sugar orange, and released a toxin, which made the root system sick, formed nodules, lost its absorption ability, and turned the nutrient supply in sugar orange yellow.

1.7 production management is not in place, which leads to yellowing.

Sometimes unreasonable pruning and ring incision are too wide and too deep to heal, and improper spraying will also cause sugar to turn yellow, too many leaves and too dense nutrients to supply, and too many fruits to supply.

1.8 Yellowing caused by virus infection

Yellowing caused by virus infection, also known as citrus Huanglongbing, is the most important disease of citrus at present. At the early stage of the disease, there were 1 ~ 2 branches in the middle and upper part of the crown, including uniform yellowing and mottled yellowing. Huanglongbing leaves become hard, brittle and dull. If the infected sugar orange is not well managed, the whole plant will turn yellow and the root system will rot seriously within 1 ~ 2a. Huanglongbing is a devastating disease because it is spread by seedlings and insects. Once you get sick, there is no cure, and the disease spreads quickly.