1. Causes of sugar orange yellowing

1.1 Severe soil acidification and hardening

Soil acidification in southern my country is quite serious. On the one hand, it is caused by acid rain under the influence of weather. , on the other hand caused by the long-term single use of chemical fertilizers. A soil pH value between 3 and 5 is not conducive to the growth and reproduction of beneficial bacteria. Reduced activity of beneficial bacteria in the soil will cause soil hardening and poor ventilation, causing the sugar orange root system to fail to grow and renew normally, causing root aging and tree decline and yellowing. .

1.2 Insufficient soil organic matter content

Most soil organic matter content in southern my country is less than 1%, and only when the content is around 3% can crops grow and develop normally. Organic matter not only provides carbon and other nutrients to plants, but also provides a place for biological bacteria to live and reproduce, improving the ability of our soil to retain water and fertilizer. For the sake of convenience and trouble, some farmers only apply chemical fertilizers 2 to 3 times a year and do not apply organic fertilizers. Therefore, the sugar oranges do not receive a reasonable and sufficient nutrient supply and grow slowly, causing the tree to become weak and yellow.

1.3 Insufficient medium and trace elements

Most farmers only focus on the application of nitrogen, phosphorus and potassium without supplementing the medium and trace elements. Sugar oranges will turn yellow due to lack of magnesium, zinc, iron and other elements. . Symptoms of magnesium deficiency in sugar oranges include mottled yellowing on the mesophyll of old leaves, while the main veins and bottoms of leaves remain green, forming an inverted V-shaped yellowing; iron deficiency is mostly seen on new leaves, which are normal in size, but the entire leaf surface remains green. The new leaves are chlorotic and uniformly yellow; the symptoms of zinc deficiency are also shown on the new leaves, the leaves are uniformly yellow, and the severe leaves become slender. Elemental deficiencies are sometimes caused by a lack of multiple elements at the same time, especially in orchards that have just begun production. Fruit trees will take away a large amount of medium and trace elements every year when they bloom and bear fruit. Once fruit trees lack boron and magnesium fertilizers, they will not be able to bloom and bear fruit normally. Using hormones to preserve the fruit, the fruit will have rough skin, dull texture, poor taste, and cannot be sold at a good price. If the medium and trace elements cannot be supplemented in time, the fruit trees will quickly turn yellow.

1.4 Yellowing caused by poor drainage

Many farmers plant sugar oranges in paddy fields in order to obtain early and high yields. Since most of the paddy fields are low-lying and have high water levels and poor drainage, if it rains continuously, the entire orchard will be soaked by water. In addition, sugar oranges are originally dry land crops. If the water is seriously accumulated for too long, the roots will rot and cause the tree to turn yellow. After the rain, some farmers saw that the fruit trees were not growing well and thought it was a lack of fertilizer, so they bought some chemical fertilizer and applied it. If applied improperly, it will accelerate the rot of the root system.

1.5 Yellowing caused by poor grafting interface healing

Since the sugar orange seedlings currently planted are all grafted seedlings, sometimes yellowing may occur due to poor nutrient transport due to poor affinity. yellowing, or the cambium layer is not aligned during grafting, causing poor transportation and causing yellowing.

1.6 Yellowing caused by nematode damage

The root nodule nematode absorbs all the nutrients in the sugar orange root system and releases a toxin that causes the root system to become diseased and form nodules, losing the ability to absorb, causing Sugar oranges turn yellow due to insufficient nutritional supply.

1.7 Yellowing caused by improper production management

Sometimes unreasonable pruning and excessively wide and deep girth cannot heal, causing yellowing. Improper spraying can also cause yellowing of sugar. If the remaining shoots are too dense and too dense and the nutrients are not supplied, it will also cause yellowing. If the fruit is too dense and the nutrients are not supplied, it will also cause yellowing.

1.8 Yellowing caused by virus infection

Yellowing caused by virus infection is also called citrus greening disease. It is currently the most important citrus disease. In the early stage of the disease, it is mostly from the crown of the tree. 1 to 2 branches in the upper part begin to turn yellow, with uniform yellowing and mottled yellowing. The leaves of Huanglongbing become hard, brittle, and dull. If susceptible sugar oranges are not managed properly, the entire plant will turn yellow within 1 to 2 years, and the root system will rot seriously. Huanglongbing can be caused by the virus in seedlings or by insects. Once infected, there is no way to treat it, and the disease spreads quickly, making it a devastating disease.