Watermelon root knot nematode disease control
At present, it is the grafting season for watermelon seedlings in greenhouses. Many readers report that in recent years, root knot nematode disease of watermelons in greenhouses has been very serious. Especially in old watermelon sheds, most of them have nematode diseases. I do not know how to control them.
Jia Dengsan, Senior Agronomist, Changle County Agriculture Bureau: Watermelon root knot nematode disease is a nematode disease caused by nematode infestation. It harms the roots of watermelons, with the heaviest damage to lateral roots and fibrous roots. The author investigated watermelons produced in Changle, Shouguang, Qingzhou and other counties and cities, and planted watermelons for more than 10 years. The sheds accounted for about 70%, of which half of the sheds were more than 20 years old. Most of these old watermelon sheds have nematode disease, which is generally reduced by 20% due to illness, and severely reduced by more than 50%%. In addition to endangering watermelon, the disease also harms crops such as tomato, melon, cucumber, eggplant, lettuce, kidney bean, celery, and cabbage, and has become a major disease in the roots of melons and various vegetables.
First, the harm symptoms and pathogenesis. The roots of the affected watermelon produce spherical or conical shaped root nodules of varying sizes. They are initially white, soft, and later turn to light yellow or dark brown. The surface is rough and sometimes cracked. The nodules can be seen in milky white or light yellow. Small insect body. The larvae suck the nutrients in the crops and hinder the absorption of water and fertilizers by the roots, which seriously affects the growth and development of the plants. At the early stage of disease, the symptoms of the plant were not obvious. The culms with severe disease grew slowly, the leaves became smaller, and the leaves turned green and turned yellow. The results were small and small. The wilting occurred at noon on sunny days, and the disease gradually became yellow and finally died. Because the environment of the greenhouse is suitable for the breeding of nematodes, it occurs throughout the year and the incidence is more severe than that of the open field. In recent years, with the expansion of the watermelon area in the greenhouse, the phenomenon of heavy cropping and continuous cropping has become more and more common. In addition, prevention and control have not kept pace, and the damage caused by watermelon nematode disease in greenhouses has become increasingly serious.
Watermelon root-knot nematode disease winters in eggs and two-instar larvae in the soil of watermelons and other hosts. Larvae suck nutrients in the roots of crops and continue to spawn, creating new generation larvae. Infested soil, diseased roots, agricultural operations, irrigation, and running water are the main routes of transmission. Unripe organic fertilizer with disease, and diseased seedlings is the primary source of infection of the disease, it can survive in the soil for 1-3 years, the longer the duration of continuous illness, the heavier the disease. The soil temperature was 25°C-30°C and the water holding capacity was 40%-50%. The nematode was rapidly bred. The larvae stopped their activities when the soil temperature was lower than 10°C and higher than 36°C, and died at 55°C for 10 minutes. High-desert terrain, loose soil, and neutral sandy loam are the most suitable for their activities and can easily explode. Soil wet sticking is not conducive to its activity and reproduction.
Second, prevention and control measures: Root knot nematode disease belongs to soil diseases, spread widely, once the soil is contaminated by it, it is difficult to remove, relying on a single prevention and treatment measures, it is difficult to achieve the desired results. According to the characteristics of its disease, we must implement the principle of "prevention first, comprehensive prevention and control" before we can receive good results:
(I) Restoring the soil's good ecological environment is a fundamental prevention and control measure. The extensive use of chemical fertilizers leads to a deterioration of soil ecology, which is the root cause of soil-borne diseases and nematodes. The microorganisms in the soil are divided into probiotics and harmful bacteria (including nematodes). Beneficial bacteria can improve the soil and promote crop growth. However, they need to rely on organic matter to survive and reproduce. The extensive use of chemical fertilizers results in a significant reduction in soil organic matter, which leads to a deterioration of the living environment of beneficial bacteria. In the absence of organic matter, harmful bacteria enter the plant body to absorb the nutrient survival and reproduction of the crop, and the formation of beneficial bacteria and harmful bacteria is in a negative relationship. Without the inhibition of beneficial bacteria, harmful bacteria will multiply, which will inevitably damage the survival of crops. Therefore, increasing the use of organic fertilizer, improving soil organic matter, and restoring the soil's good ecological environment are fundamental to the prevention and control of soil-borne diseases. The 4 mu greenhouse watermelon in Zhangnan Village of Changle County, Guanong Zhang Qirui, although it was planted for 22 years, he insisted on increasing organic manure and reducing the amount of chemical fertilizer to increase soil organic matter content and cooperate with crop rotation. Effectively control the harm of nematodes and ensure the high yield and quality of watermelon.
(b) Rational rotation for change. More than two years of crop rotation with grasses or onions and garlic crops have good control effect, and the effect of the implementation of crop rotation is better. Rotation can break the food source of nematodes, making it impossible to survive. In Changle County, it was investigated that the sheds with more severe disease were changed to planting onions and garlic crops and grass crops three years later.
(c) Frozen treatment of soil. After the crop is harvested, plow water is poured before and after the harvest, and the shed film is removed. After two months of freezing, the nematode can be effectively killed.
(d) high temperature stuffy shed. After the summer crops are harvested, the greenhouses are cleaned and high-temperature stuffy sheds are used: 50-100 kg of calcium cyanide ac are evenly spread on the ground per acre, and 4-6 cm long wheat straw 600-1000 kg per acre is scattered. , and then deeper than 20 cm, and then ridge, film, irrigation seal the shed after the room. When the temperature of 20 cm soil layer reaches 45 °C, it will continue to drench for not less than 7 days. After the boring shed, the film is uncovered and the sun cools. It is better to use sun exposure for 5-7 days.
(five) use disease-free strong seedlings. When purchasing seedlings from other places, we must quarantine and prevent the introduction of diseased seedlings. This is a key measure to prevent the spread of disease. Nursery should use disease-free soil, use disease-free fertilizer, and cultivate disease-free strong seedlings.
(f) Strengthen field management. In combination with site preparation, turning topsoil to less than 30 cm can reduce nematode damage. Rational fertilization water, enhance plant disease resistance. Dispose of diseased plant residues and field hosts in a timely manner and focus on incineration or deep burial to prevent transmission hazards.
(7) Control of biological agents. Most of the nematicidal chemical pesticides used in the past were environmentally polluting and unsafe to humans and animals. Most of them have now been banned. In recent years, some of the green, environmental-friendly, highly-effective, and low-toxic biopesticides such as avermectin emulsifiable concentrate have shown good efficacy. Before watermelon seedlings and planting, use 1 ml of 1.8% avermectin EC per square meter, mix well with appropriate amount of fine soil and spread the seedbed or planting ditch. When diseased plants occur in the field, the diseased plants can be watered with 1.8% avermectin EC 1500 times, 250-300 ml per plant liquid, once every 7-10 days, depending on the situation, continuous irrigation 3-4 times, can be effective Control nematode damage.
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