Root-knot nematodes are a class of plant-parasitic nematodes that cause roots to form roots and are more susceptible to other fungal and bacterial diseases.
Root-knot nematodes parasitize on many different crops (more than 2,000 plants) and can multiply quickly, coupled with a relatively short life history, the damage is quite large.
Morphological characteristics
Root knot nematodes are very small and invisible to the naked eye.
1 egg
Root knot nematode eggs, such as silkworm cocoons, are more transparent and have a tough outer shell with a length of about 0.1 mm and a width of about 0.05 mm.
2 larvae
The 1st instar larvae curled in the egg after hatching; the 2nd instar larva enters the infecting stage, and after invading the host, the worm body gradually expands and becomes a pod-like shape; the 3rd instar larvae resembles an eggplant and begins to differentiate between male and female; 4th instar The larvae have completed male-female differentiation, and the females are egg-shaped or pear-shaped, and the males are curved.
3 adults
The male adult is linear, the tail is slightly round, the color is transparent, and the body is small.
The female adult is pear-shaped or lemon-shaped, milky white, and is buried in the host tissue.
Living habit
Root-knot nematodes mainly use eggs and 2nd instar larvae to grow in the soil with root nodules, or directly in the soil, and survive for 3 years without soil host plants.
The 2nd instar larvae are infested by root-knot nematodes and usually invade by the root tip. The nematode grows to the 4th instar in the root knot or nodule of the host. The male and the female mate with each other. After the mating, the female lays eggs in the root knot, and the male worms out the host tissue and enter the soil to die naturally.
The eggs in the root knot hatch into 2nd instar larvae, leave the host and enter the soil, and re-invade the host for a while or stay in the soil for winter.
Biological characteristics
When the soil temperature reaches 10 °C or above, the eggs can hatch and the larvae move more than 1 to 20 cm in the soil layer. Soil temperature above 40 ° C or below 10 ° C rarely active, temperature 55 ° C, 10 minutes to death.
Suitable soil relative humidity of 40% to 70%. In dry or wet soils, its activity is inhibited. Suitable soil pH 4 ~ 8. The conditions of loose soil texture and low salt content are suitable for nematode activity, which is beneficial to the disease. Generally, sand is heavier than clay, and the incidence of continuous cropping is heavy.
Root-knot nematodes occur in the shed for about 10 generations a year, and each female lays about 300 eggs. The larvae are mobile endoparasites, and the females are fixed internally. The 2nd instar larva punctures into the root of the host plant, forming a feeding site near the vascular bundle, and the cells around the head region fuse to form giant cells.
The distribution of nematodes in the soil of the greenhouse is common. As the distance from the front edge of the greenhouse increases, it shows a trend of increasing first and then decreasing gradually. In other words, the edge and center of the shed are less distributed.
Root knot nematode damage
Root-knot nematodes are often more than 30 kinds of vegetables such as melons, solanes, beans and radishes, carrots, lettuce and cabbage. It is not to be underestimated for grapes, citrus, bananas, dragon fruit and so on.
1 Vegetable victimization
The root-knot nematode directly harms the roots of the vegetables, and the roots of the affected crops are knob-like, poorly growing, and the roots are rotted. Due to the influence of the root system, most of the affected plants had slow growth in the early part of the ground, and the leaves became smaller and yellower. They were in the form of no-fat, no-healing or poorly-growing. In severe cases, the growth was stagnant, the internodes were shortened, and the plants were short or even wilting.
Root-knot nematode destroys the normal differentiation and physiological activities of root tissue, the transportation of water and nutrients is hindered, the photosynthesis is reduced, the fruit often deforms or the coloration is uneven, resulting in a decrease in yield and a decrease in quality.
Symptoms are similar to those of cruciferous clubroots. In 1855, Berkeley MJ first reported that the pathogen of cucumber root knot disease in the greenhouse was root-knot nematode. At this point, root knot nematodes and clubroot disease are distinguished.
Tomato, eggplant: The root tip of the root forms a mung bean or millet-sized spheroidal tumor and a small root knot, and no small lateral roots are produced on the root knot. In severe cases, multiple root nodes are connected together to form tumors of different diameters.
Bitter gourd and cucumber: nodules or roots of different sizes are formed on the lateral roots or fibrous roots. Multiple root knots are connected, which are irregular in shape, have cracks on the surface, and are rough and perishable in the late stage.
Celery, pepper and cowpea: The lateral roots and roots are the most vulnerable, and a large number of nearly spherical root knots are formed on the root of the disease, which are connected like a bead.
2 Fruit tree victimization
Mainly damages the roots, causing the root tissue to overgrow, resulting in the formation of nodules of varying sizes. The roots are nodular, which is the main symptom of the disease. Most of the nodules occur on fine roots. When the infection is severe, secondary nodules can occur, and a large number of small roots occur, causing the roots to form a mass and form a fibrous root mass. Because the root system is damaged, it affects the normal function, making the water and nutrients difficult to transport, and the old cooked root nodules rot, and finally the roots are necrotic.
In the general incidence, there is no obvious disease in the aboveground part of the diseased plant, but as the root system becomes more and more serious, the crown has weak conditions such as weak branches, small leaves and declining growth. When the damage is heavier, the leaves are yellowish, the veins are swollen, dull, and the leaves are curled, showing a lack of water.
Citrus damage: its young root tissue overgrows, forming root nodules of different sizes, with the most severe damage to fine roots and small roots, forming nodules of varying sizes on the root tip, spinning or irregular shape, near sesame seeds The mung bean is large, initially milky white, and then turns yellow-brown to dark brown, and the root hair is thin.
In severe cases, secondary nodules can also occur, causing the entire root system to form a fibrous root group with a fibrous nodule, old root nodules, and root necrosis. There is no obvious symptom in the early part of the diseased plant. As the disease is aggravated, the crown shows weak branches, yellowing, curling, falling off, and even the branches die.
Grape damage: Root knot nematodes in the soil through the sensitive tissue of the head to find the grape roots, mainly invading the young parts of the roots, it can pierce the root cell wall, and inject toxic substances secreted by the esophagus, causing changes in the grape roots, and then affecting The upper part of the grape grows.
The nucleus divides but the cytoplasm does not separate, forming multinucleated giant cells. This easily causes tumor formation and excessive branching in the roots, which easily leads to cell death, and also facilitates the infestation of grapes by other pathogens.
Banana damage: mainly damage the roots. A nodule (root knot) of different sizes is formed in the root, and the end of the thick root is swollen into a drum-like shape or a longitudinally curved shape, and the roots are less, dark brown, and the epidermis rots in severe cases. Because the 2nd instar larvae are young and invasive to the new roots, after invading the roots, they grow with the roots, absorb nutrients in the banana roots, form giant cells in the affected parts, and a large amount of tissue phloem in the phloem, xylem enlargement, and obstruction of the catheter.
The growth of roots is affected and the growth of the aboveground part is weak. The initial symptoms are not obvious. Generally, the leaves are yellow, the plants are short, and they are short of water and lack of fertilizer. In the later stage, the leaves are yellow, withered, the buds are difficult, the fruits are thin, and the plants are small. Premature aging.
Pitaya is affected: root-knot nematode disease causes root tissue to become black and rot, and some roots produce globular root knots. After the nematode invades, the irregular roots and the roots of the roots and the roots produce irregular tumors of different sizes, that is, the root knots, which are yellow-white at first, smooth in appearance, brown in the back and broken and rot. After the nematode parasitization, the root function was destroyed, which caused the plant to grow weak and yellow, which affected the yield.
The roots damaged by nematodes are prone to wounds, which induce complex infection of root pathogenic fungi and bacteria, which is aggravated. Often causes ulcer disease to occur repeatedly.
Root knot nematode prevention and treatment method
For the prevention and control of root-knot nematodes, it is necessary to clarify the central idea of ​​“preventing prevention and supplementing by treatmentâ€. The following precautions are described below.
For shed vegetables:
(1) high temperature shack, soil treatment
Use most of the summer heat to kill most nematodes. At the same time, the plant residues that the root knot nematode lives on can be decomposed.
It is mainly treated with a quenching soil treatment agent. After treatment, the biological fertilizer and organic fertilizer are applied before the squat.
(2) Deeply turning the soil
It is required to plow the depth of 25 cm or more, so that the nematodes in the deep layers of the soil turn to the soil surface, and the surface soil is loose, and the soil water content after sun exposure is reduced, which is not conducive to the survival of the nematodes.
(3) timely removal of sick bodies, grafting cultivation in seriously ill
Timely remove the roots, diseased plants, sick bodies, weeds and concentrated burning in the vegetable shed, and wipe or disinfect the agricultural tools used in the ward to prevent the spread of root-knot nematode disease.
In the case of serious disease, the grafting method can effectively improve the disease resistance of the plant, and the symptoms of the aboveground part are obviously alleviated, and the effect is better.
For fruit trees:
(1) It is strictly forbidden to transfer seedlings from the ward and disinfect the seedlings before transplanting.
It can be immersed in hot water at 48 ° C for 15 minutes before transplanting.
(2) Adding organic fertilizer and strengthening cultivation management
Appropriate application of organic fertilizer to enhance the tree's potential and reduce damage. In addition, if the soil is heavier, the soil can be effectively reduced every year.
(3) After killing the nematodes, raise the roots in time
Traditional nematode drugs can only cure diseases and cannot raise roots, which can not bring real benefits to farmers. Therefore, after taking the medicine, the roots should be raised in time to ensure roots and restore root activity.
More pesticide knowledge , please pay attention to China Pesticide Network
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