Is soil nematode a worm? What are the hazards? How to kill? (with prevention and control methods)

The number and species of nematodes in soil are abundant. Soil nematodes are widely distributed in all kinds of soils, and the number of soil nematodes varies with different soil depths, among which the soil nematodes distributed in the 10-20cm soil layer are the most. As one of the leading killers of common soil-borne diseases, nematodes do great harm to agriculture. With a length of only 0.3-6mm, it is almost invisible, but it is related to more than 50% of soil diseases, such as perforated nematodes, root-knot nematodes, cyst nematodes, stem nematodes. A variety of nematodes have reduced the production of agricultural industries in related fields by 5%, 20%, and local production by 60% or even no harvest. Is soil nematode a worm? What are its harms? How to kill and prevent?

1. Harm of nematode disease

"the most important feature of nematode disease is that it has no characteristics." Said Wang Xinrong, a professor in the Plant nematode Research Office of the School of Agriculture, South China Agricultural University. It is said that it has no characteristics, in fact, because it does not pay enough attention to make nematode disease often confused with other pathogenic diseases, can not prescribe the right medicine for natural prevention. The neglect of nematode diseases and improper response methods have seriously challenged the agricultural economy.

On the one hand, the harm of plant nematodes to plants comes from the mechanical damage caused by mouthparts to the roots, stems and leaves of plants during parasitism. The exogenous wounds caused by these physical attacks promote the infection of pathogens such as fungi, bacteria and viruses to plants, making them "susceptible" to a variety of plant diseases. On the other hand, the "biochemical skills" of nematodes also make plants miserable. Digestive juices and a variety of enzymes secreted during eating enter the circulatory system of plants, disrupt and destroy the normal metabolic function of plants, and affect their growth and development.

two。 The symptom of nematode disease is not obvious

Most plant nematode diseases have no obvious specific symptoms, which are similar to element deficiency in the field, mainly for plant growth weakness, dwarfism and yellowing, and yield decline. But if you observe carefully, the "ghost" of the nematode has nowhere to hide. The activity of plant parasitic nematodes is limited, and the ability of autonomous migration in the process of parasitism is weak. without the interference of human factors, the maximum radius of influence is only 1 meter in a year. The plant community parasitized by nematodes was distributed as a small block and withered and yellowed in the field, which was different from plant deficiency and soil water and fertilizer deficiency, while the wilting and yellowing of the latter was distributed in whole or whole rows.

Nematodes can not only harm plant roots, but also destroy stems, flowers and seeds to be harvested. The typical symptom types of plant nematode diseases can be divided into aboveground and underground parts. Among them, the aboveground parts are mainly characterized by twisted leaves (daffodils, strawberries, rice, etc.); stem swelling, distortion and decay (coconut, potato, sweet potato, etc.); flowers change color and rot, inflorescences become shorter, sterile florets increase (chrysanthemum, etc.); galls are formed, seeds do not form starch (wheat, etc.), or even the whole plant dies (pine, etc.). The underground symptoms are mainly root knot (cucumber, peanut, citrus, etc.) and root necrosis and decay (banana, etc.). These seemingly frequent symptoms of the disease often make growers take it lightly, thinking that spraying pesticides is done, but nematodes cannot be killed, and no matter how much investment is in vain.

3. How to simply distinguish whether it is a nematode disease?

In terms of the highest incidence of root-knot nematode disease, the plant roots and underground organs harmed by parasites form tumors, called root knot, with irregular distribution. The adventitious whisker root can also grow on the root knot, and the fibrous root forms a root knot after being infected repeatedly, thus forming a disorderly hair-like whisker root mass, while the aboveground part shows declining symptoms such as growth dwarfism and yellowing. If the root knot is cut open for sampling, a large number of worms can be observed under the microscope. Compared with the root knot, the common root nodule of legume is caused by the symbiosis of rhizobium and plant. the shape of the root nodule is regular and often grows on one side, and the red-green bacterial liquid overflows in the open nodule.

4. Prevention in advance is the key.

Wang Xinrong said that nematode diseases are really at the later stage of the disease, and it is very difficult to control them, so prevention should be given priority. "Farm tools can be a medium for transmission of water contaminated by nematode eggs." At the same time, the daily planting management is not standard, will also become an "accomplice". Inadvertently bringing the soil, seedlings and farm tools from the infected place to the healthy plants can lead to the rapid spread of the disease. Therefore, the land should be disinfected by drying, fumigating, stuffing, mixing tea and lime before sowing, and the permafrost in Northeast China also has a similar effect. Conditional addition of microbial line-killing organic fertilizer after disinfection, the most important thing is to strictly check the water source and agricultural tools, while ensuring disease-free flow into seedlings and seeds.

5. How to kill soil nematodes? Control methods of nematodes

Plant quarantine: prevention and control of overseas nematode invasion

Agricultural control: disease-resistant varieties, disease-resistant rootstocks, rotation, soil improvement

Physical prevention and control: high temperature greenhouse, water flooding treatment, lime nitrogen, ultrasonic wave, ray

Biological control: plant sources, microbial sources, predatory nematodes, insects, mites

Chemical control: the most effective method, fumigation and non-fumigation agents.

Among them, chemical control is still the most important control method, and the utilization rate accounts for more than 80% of the total control methods. The commonly used avermectins are trigger nematodes with fast killing speed and low dosage, but they are easily absorbed by soil aggregates in the soil and rapidly degraded by microorganisms. the advantage is less pollution, but the disadvantage is that the duration of nematode prevention is short. it can only kill nematodes in rhizosphere soil and is ineffective for invading plant roots. In addition to contact, thiazophos can also be absorbed and transmitted to plants to kill nematodes in roots, but excessive dosage can burn roots. Generally, the combination of avermectin and thiazophos can make the efficacy complementary and avoid the emergence of insect resistance, and chitin, which can induce crops to produce chitinase, is also often combined with them. Chitinase can decompose the chitooligosaccharides in nematodes and eggs and dissolve the nematode walls and eggshells. Since the life history of nematodes is about 20 days, it takes a generation for drug efficacy statistics to be accurate.

In addition to chemical control, environment-friendly biological control dominated by microbial insecticides has also become a hot spot year by year. Safety, growth promotion, sustainability and soil improvement, biological agents have obvious advantages, but high costs, can not be mixed with fungicides and high technical requirements are also testing the forerunners in the industry.