What is the disease of a lot of dirt on citrus leaves?

Sometimes, in the citrus orchard, we will find that a layer of black things will appear on the leaves or branches of the citrus, and it will disappear after gently wiping it off, making us think that it is just dust on the side of the road. Is this really just dust? Or is it a disease that affects fruit yield?

Actually, it could be citrus soot disease! In some places, it is called coal stain disease, which is a fungal disease, mainly affecting leaves, branches and fruits, and affecting the healthy growth of citrus.

SymptomsIn the early stage of the disease, a layer of dark brown mold spots will grow on the diseased area, and gradually expand, and finally a fluffy black and dark brown mold layer will be formed, and small black dots will be scattered.

Soot disease can seriously affect the plantPhotosynthesis, which leads to an obstacle in the nutrient supply of fruit trees, which weakens the tree and affects fruit yield.

The causative agent of regular soot disease is overwintering in the diseased parts of citrus through mycelium, conidia, closed cyst shell and other forms. By the spring of the following year, it spread through wind and rain.

The pathogens are mainly aphids and scale insects.

The secretion of whiteflies acts as nutrients**. It is generally found in shady, damp or poorly managed citrus orchards.

Soot disease can occur throughout the year, but the high incidence period is mainly concentrated from May to September.

The main reasons for this are that the park management and cultivation planning are not done well, the management is not in place, the planting is too dense, the concealment is not ventilated, and even the excessive application of nitrogen fertilizer will lead to the occurrence of soot disease.

Prevention and control methods1.Agricultural control: strengthen the management of orange orchards, and wash the mold layer with water when possible.

First of all, it is necessary to ensure that the orchard has good ventilation and light transmission, which requires attention to the pruning of the orchard. At the same time, pay attention to reducing the humidity in the orchard. And we must enhance the stress resistance of fruit trees and do a good job in pest control.

2.Clearing the garden: Eliminate the source of insects and reduce the probability of pests and diseases.

After the fruit is picked every year, pay attention to collect the diseased branches and dead branches in the park, take them out of the orchard and burn them intensively, and then spray 3-5 degrees of stone sulfur mixture in the orchard.

You can even sprinkle lime powder on the foliage.

Promotes the shedding of mold layers.

3.Chemical control:25% difenoconazole can be used.

2000 times + 20% fluridine 2000 times, 25% pyraclostrobin.

2000 times + 30 thiamethoxam.

2000 times, 80% mancozeb 1000 times + prochloraz 750 times + 26% chloroflurididol 1000 times for control.

It's citrus soot disease. It is a fungal disease that mainly damages leaves, branches and fruits, and affects the healthy growth of citrus. If the cultivation planning is not done well, the management is not in place, the planting is too dense, the concealment is not ventilated, and even the excessive application of nitrogen fertilizer will lead to the occurrence of soot disease.

It is necessary to pay attention to the pruning of the orchard, pay attention to reducing the humidity of the orchard, and do a good job in pest control.

Citrus leaves have a lot of dirt, which is often referred to as bituminous coal disease. Citrus bituminous coal disease often occurs on the surface of leaves, branches and fruits, like a layer of brown bituminous coal, which can be wiped by hand. Bituminous coal disease is a fungal disease, the fungus attaches to the surface of the leaves and fruits, feeds on the secretions of pests such as scale insects, whiteflies, aphids, etc., and produces a layer of black-brown things.

And then through the reproduction of germs, the bituminous coal disease continues to expand. Although bituminous coal disease is not as serious as other pests and diseases, it also seriously affects photosynthesis and affects fruit quality. The high incidence of citrus bituminous coal disease, generally speaking, there are two main factors, one is that the orchard is closed and not ventilated, and the interior is humid and warm, which is conducive to the reproduction of pathogens, and the control effect of the medicine is poor.

Second, there is a high incidence of scale insects, whiteflies, aphids and other pests, which provide abundant food for pathogens.

This is citrus red (spider disease).

It mainly damages citrus leaves, branches and fruits. When the damaged leaves and fruits are severe, they turn gray and white, lose their luster, until they turn yellow and fall off. The peak seasons are from April to June and September to November. [9]

Control measures: strengthen inspection, an average of 5-6 insects per leaf should be controlled.

Do a good job of clearing the garden in winter, and choose 100 times the liquid of spraying oil emulsion or Baumé stone sulfur mixture before germination in the next year in winter.

When the insect population reaches the control index, it can be controlled or treated with acaricides, and broad-spectrum household drugs are used less to protect natural enemies.

tatter leaf virus

Symptoms (Figure 2-3).

Figure 2-3 Citrus leaf crushing disease.

1.Trunk pathology (citrus aurantium anvil) 2Diseased leaves (Citrus aurantium) 3Normal leaves (Citrus aurantium).

The scion above the ring and interface at the citrus grafting joint is swollen, and the leaf veins are yellowed, similar to the yellowing caused by annular peeling, and the plant is dwarfed. Driven by external forces such as strong winds, the joint (grafting joint) of the rootstock of the diseased tree is easy to break, and the section is smooth. After infection with citrus aurantium citrus orange as rootstock, the new leaves showed yellow spots and the leaf margins were defected and distorted.

When citrus excelsa is used as a rootstock, the new leaves appear yellow spots, twisted and broken into unevenness, so it is named. The Mexican lemon was used as the rootstock, and yellow-white spots and bright veins appeared on the leaves. When the local orange was grafted on the orange in the early stage, the leaves appeared yellow-white spots, deformed, shrunken, and smallened, and the yellow-white spots appeared on the stems, which were distorted, and the yellow-white spots never faded and changed.

When the local early grafting on Citrus aurantium, the anvil part of the panicle appeared large at the top and small at the bottom, the leaves were yellowed or yellow and white spots, shrunken, deformed, small leaves, dead branches, and the plants were dwarf, and did not flower and bear fruit. The graft is hanged, broken, and finally dies.

The pathogenic citrus leaf crushing disease is a virus with virion-shaped particles, with a size of 450-920 19 nm.

Patterns of occurrence. Citrus aurantium, citrus aurantium, Troia citrus orange, Mexican lemon and thick-skinned lemon are easy to develop diseases when they are used as rootstocks, and wolfhead orange is disease resistant. The above varieties were used as rootstocks to graft local early oranges, machines, milk oranges, ponkans, banana oranges, oranges, crystal pomelo, Beijing lemons, Wenzhou mandarins, early oranges and vermilion varieties. Citrus aurantium and pachyderma citrus can be used as indicator plants to identify leaf crushing virus, and the shortest time to show symptoms is 25 days, generally about 60 days.

Citrus aurantium is more sensitive to leaf crushing virus than thick-skinned lemon, and the symptoms are easy to manifest when the temperature is low, and the symptoms can be manifested in late March and mid to late May. Symptoms are not easy to show during high temperatures from June to August, and they do not show symptoms until the following year. Cowpea was used as an indicator plant, and the symptoms of reddish-brown blight showed 3-5 days after inoculation.

The rootstock was grafted early, and it showed yellowing, weakness and death at the seedling stage in Zhejiang, while it took 6-8 years to show obvious and serious symptoms in the Neijiang area of Sichuan. The local grafting with red orange and wolfhead orange as rootstocks is early, showing disease resistance, and the tree is vigorous and abundant.

In Taiwan, citrus aurantium is used as the rootstock of citrus, banana mandarin, orange and crystal pomelo, and the leaf crushing disease is serious; In Sichuan, citrus aurantium is used as the rootstock of mandarin orange, banana mandarin and orange, and it almost does not show symptoms, which may be related to the environment, climate, soil quality, etc.

Prevention and control methods1.Choose disease-resistant (resistant) rootstocks.

In Zhejiang, the local varieties such as early orange, early orange, milk orange and mallete orange are rarely grafted with wolfhead orange as rootstock. In Sichuan, red oranges can be used as rootstocks; Ponkan and orange can be used as rootstocks. In Taiwan and southern China, sour oranges are used as rootstocks for banana mandarins, ponkans, and Xinhui oranges, and symptoms are rare.

2.Cultivating disease-free seedlings.

Through the identification of indicator plants such as cowpea, disease-free mother trees were selected to collect scion and cultivate disease-free seedlings.

3.Cutting down seriously diseased trees and managing lightly diseased trees requires the use of special tools to prevent contact infection.

Leaf crushing disease is a disease of citrus trees that use citrus aurantium and orange as rootstocks. After the infection of Citrus aurantium anvil, the grafting joint is annularly shrunk, the interface is swollen, and the obvious yellow ring appears, and the rootstock part is atrophied, resulting in separation, hand push or strong wind, easy to break at the grafting interface, and the crack surface is smooth. The crown yellowing of the diseased plant was obvious, from the yellowing of some leaf veins in short strips to the yellowing of all leaf veins and leaves, and the root system was aging and necrosis.

Diseased plants grow and dwarf, and even die. The new leaves of citrus aurantium (such as Rusk, Troya, etc.) showed yellow spots and leaf margin defects and distortions after infection, among which C. lusk was the most sensitive to this disease and could be used as an indicator plant. After Pachyderm lime infection, new leaves appear yellow spots and leaf margin defects.

Other general varieties have no obvious symptoms after being infected. In addition, the virus infects cowpea and broad beans with withered spots on inoculated leaves, and produces yellow spots on inoculated leaves and new leaves after infection with Quinoa, and infects Cleveland smoke, causing mild mottling and mosaic symptoms in the system.