Causes of Citrus Tree Yellowing and Control Methods

Citrus is one of the most popular and very common fruits. But in fact, growing citrus is not easy, and yellowing is very prone to occur. So what causes citrus tree yellowing, and are there any ways to control it? Regarding these, the Tuliu.com editor will give growers a brief introduction, hoping to bring help to growers.

I. Causes of citrus tree yellowing

1. Soil waterlogging

When citrus is planted in some low-lying areas, because the water table underground is high, and then the rainy season comes, it is easy for the citrus root system to be waterlogged and suffer for a long time, resulting in poor root absorption capacity. The citrus tree is in a yellowing state, which is what people call an “aging tree”. There is also the fact that southern soil is generally acidic, so citrus tree roots cannot effectively absorb nutrients, directly leading to reduced growth of branches and leaves, and the tree body remains yellowing and stagnant for a long time.

2. Phytophthora in the soil

Citrus tree yellowing is also caused by rampant activity of harmful microorganisms such as Phytophthora in the soil, directly leading to phenomena such as root rot, loss of the absorption capacity of citrus roots, and the citrus tree remaining in a semi-starved state for a long time, so yellowing naturally occurs. There is also the fact that even if bio-fertilizer is used, if it is not decomposed, when the raw fertilizer dissolves and ferments, the harmful microorganisms produced cause damage to the root system; especially when the fertilizer is excessive or the concentration is too high, root rot is particularly likely to occur. And it is difficult to recover, which leads to the slow growth of the citrus tree body, and the branches and leaves are sparse; over time, tree yellowing will appear.

3. Improper pesticide application

Another issue is improper pesticide application to citrus trees, for example when the concentration used is relatively high, especially when the temperature is too high, causing citrus trees to drop leaves or produce mottled yellowing leaves, resulting in overall yellowing of the citrus tree. Citrus root-knot nematodes parasitize under the root bark, mainly harming the citrus tree roots, causing the root tissue to divide because of the root-knot nematodes, forming root galls of different sizes, reducing fibrous roots, and finally causing the old roots to rot because of the root galls, with the root bark becoming moldy and rotten, weak attracting ability, and nutrients in the soil not being absorbed; if this continues for a long time, yellowing will appear, and when yellowing reaches a certain degree, it will directly affect yield.

4. Improper use of herbicides

Some growers, in order to save labor and time, use large doses of herbicides; the pesticide residues will continuously accumulate in the soil, destroy the soil's physical and chemical properties, aggregate structure and porosity, kill beneficial microorganisms, and affect the absorption of citrus tree roots; over time, yellowing will naturally appear. Finally, the branches and leaves of the entire citrus tree turn yellow, and the symptoms are similar to the yellowing type harmed by root-knot nematodes, making it very difficult to distinguish.

II. Countermeasures for citrus tree yellowing

1. Soil improvement

Creating a good living environment for the root system is the most important thing. At the same time, carry out timely drainage and irrigation, especially in rainy seasons, pay special attention to the roots of citrus trees and observe whether soaking has occurred, and at the same time open ditches well to thoroughly drain the accumulated water at the citrus tree roots, preventing soil oxygen deficiency and causing root mildew and rot. Be patient and meticulous with citrus trees, observe at all times, and solve problems promptly when they arise. Only in this way can citrus tree yellowing be effectively prevented.

2. Scientific fertilization

For scientific fertilization, the topdressing method should be changed: dry application, raw application, water application and decomposed application. When opening fertilization ditches, be careful not to reach many roots; for mature fruiting orchards, broadcast outside the drip line of the tree canopy, and at the same time remember to mix well with soil, then cover with loose soil. If the weather is dry, irrigate promptly after fertilizing. The fertilizer types should mainly be organic fertilizers with various elements, and bio-organic fertilizer plus trace elements can also be used and applied together. In this way, conditions such as yellowing caused by nutrient deficiency and fertilizer damage can be alleviated. There is also tree yellowing caused by root-knot nematodes: Bordeaux mixture granular insecticide can be used, scattered around the citrus tree roots, so that root-knot nematodes will be killed, effectively reducing the harm of root-knot nematodes in the soil.

3. Standardized use of pesticides

For the standardized use of pesticides on citrus trees, special attention should be paid to high temperatures and to controlling pesticide use during the young shoot and young leaf stage, especially pesticides prohibited for use on citrus trees as stipulated, which must be strictly prohibited according to the instructions; special attention should also be paid to the wide variety of pesticides on the agricultural input market, which must not be used casually. It is even more necessary to avoid using counterfeit and inferior pesticides, and even more so not to randomly add and mix various pesticides for use. This is to avoid harming citrus tree leaves and causing yellowing. Only by strengthening cultivation management and improving tree resistance can citrus tree yellowing be effectively controlled.

I do not know whether introducing so much is helpful to growers; I hope that under scientific management, growers can have a good harvest.