Control Methods for Root-Knot Nematode Disease in Hami Melon
Root-knot nematode disease is an important disease of Hami melon, occurring and distributed in some areas. It can develop both in protected cultivation and in open fields, with more severe occurrence in autumn. Infection at the seedling stage has a great impact on production. After the disease develops, the rate of diseased plants often reaches more than 60%, significantly affecting Hami melon production.
The symptoms mainly affect the root system, producing many milky-white root knots of varying sizes on the main root and lateral roots. When the root knots are cut open, white translucent pear-shaped nematodes can be seen. In the late stage of the disease, the diseased roots darken in color and eventually rot. The aboveground parts of the plant or seedling gradually fade in leaf color as the disease progresses, wilting from bottom to top until the entire plant dies.
The pathogen Meloidogyne incognita Chitwood is called the southern root-knot nematode. The pathogenic nematode is sexually dimorphic, with larvae being slender and worm-like. The adult male is linear, slightly rounded at the tail end, colorless and transparent, measuring 1.0-1.5mm×0.03-0.04mm. The adult female is pear-shaped, and each female nematode can lay 300-800 eggs, embedded within the host tissue, measuring 0.44-1.59mm×0.26-0.81mm.
Disease characteristics: The southern root-knot nematode can overwinter by damaging and reproducing on various vegetables in winter. In northern vegetable-growing areas, the nematode mainly overwinters as adult females in egg masses discharged within root knots, together with diseased plant debris in the soil of protected cultivation. When the temperature rises, overwintering eggs hatch into larvae, or some overwintering larvae continue to develop and become active in the surface soil layer. Upon encountering a host, they invade from the young roots, stimulating host cell division and proliferation to form giant cells, and excessive division forms tumor-like root knots. The larvae develop into adults within the root knots and begin mating and laying eggs. Eggs hatch within the root knots; first-instar larvae remain inside the eggs, while second-instar larvae bore out of the host to cause secondary infection. The disease is mainly spread through diseased soil, diseased seedlings, irrigation water and farm tools. Under conditions of soil temperature of 20-30°C and humidity of 40%-70%, the nematode reproduces very quickly and easily accumulates in large numbers in the soil. Generally, plots or greenhouses with high and dry terrain, loose soil texture, and lack of water and fertilizer suffer more severe occurrence. Usually, greenhouses are more severely affected than plastic tunnels, and plastic tunnels more severely than open fields. In addition, continuous cropping of the same crop leads to more severe occurrence.
Control methods
(1) Agricultural control.
Use disease-free soil for seedling raising. In areas where the disease frequently occurs, use nematode-free soil or field soil for seedling raising, apply organic fertilizer that does not contain diseased plant debris or is fully decomposed, or use substrate for seedling raising, while also taking care to prevent human-mediated spread.
After harvesting severely affected plots, thoroughly remove diseased root debris, and deep plow the soil 30-50cm. In late spring and early summer, carry out solar high-temperature disinfection to kill pests. That is, after clearing the previous crop, apply quicklime and chopped rice straw at 4.5-7.5t/hm2 respectively, plow and mix evenly, then dig trenches and form ridges or beds, fill with water, cover with plastic film and press it down firmly, then seal the greenhouse for 10-15 days. This can kill all nematodes, pathogens and weeds in the soil. After treatment, take care to increase the application of biological bacterial fertilizer.
(2) Chemical control.
Before sowing or transplanting, carry out soil treatment according to the nature of the pesticide. You can choose 1.8% abamectin EC at 10-15L/hm2, mix with water and apply evenly to the seedbed, or apply to the transplanting furrow or transplanting hole before sowing or transplanting. You can also use 98%-100% dazomet microgranules at 75-120kg/hm2, evenly broadcast or applied in furrows within the top 20cm of soil. After application, immediately cover with soil, sprinkle water to seal or cover with film for 7-12 days, then loosen the soil to release gas for 3-10 days before sowing or transplanting. You can also use 3% miral granule at 22.5-30kg/hm2, evenly applied to the transplanting furrows or holes.