I believe that many fruit growers who grow kiwifruit are not very unfamiliar with root knot nematodes, because this thing often occurs on the root system of kiwifruit. After the occurrence, it often causes the kiwi tree to weaken, the leaves are small and yellow, and the plant slowly dwarfs and withers to death, which has a considerable impact on the production and management of kiwifruit.
Although many fruit grower friends know that root knot nematodes often appear on the root system of kiwifruit, some people still can't tell whether this symptom is a disease or an insect pest. As a result, it is not known where to carry out control and affect the growth and production of the tree. The impact of this situation on kiwi growers is considerable, it is very troublesome to the fruit farmer friends, in order to figure out this symptom and can take effective prevention and control measures, Xiaoguo sorted out a detailed description of the kiwi root knot nematode, hoping to help the kiwi growers.
Young kiwi trees to adult trees and seedlings are infested with root-knot nematodes. The root system of the affected plant produces many round or spindle-shaped root nodules or nodules of varying sizes, i.e. galls. The small ones are like millet grains, the large ones are like soybeans, and some are also connected into beads.
Root-knot nematodes
Usually the new root nodule is small, and the old root often has a larger nodule, which is initially pale yellow, the surface is smooth and hard, and then gradually turns brown and decays. The affected root is shorter than the normal root and has fewer branches. The symptoms of the aboveground part are very similar to those of the deficiency, the plant is stunted, the growth is slow, the red-fleshed kiwi fruit is killed in May, its spring shoots are soft and sagging, the tree is weak, the leaves are small and yellow, the plant is dwarfed, the results are few, the fruit is small, and the quality and yield are seriously affected. Orchards with mild disease do not show any symptoms in the aboveground part, but yields are lower than orchards without root-knot nematode disease.
The pathogen of kiwi root-knot nematodes is root-knot nematodes, which cause harm such as southern root-knot nematodes, northern root-knot nematodes, peanut root-knot nematodes and Javan root-knot nematodes. Among them, the northern root-knot nematode has occurred in large numbers in many kiwifruit producing countries, and it is also more common in the production areas of kiwifruit in China.
The entire development stage of root-knot nematodes has three stages: eggs, larvae, and adults. The eggs are milky white and cocoon-shaped. The 1st instar larvae molt in the egg, curl in a linear shape in the egg, after hatching for the 2nd instar larvae, the 2nd instar larva invades the root system, after the invasion, it is fixed and does not move, only the head is active to feed, the 3-year larvae after molting into bean pods, the 4th instar larvae have a tail tip cone at the end of the expanded tail, at this time the sex of the insect body can be distinguished, and the 4th instar larva becomes an adult after molting.
Females of adults are spherical, pear-shaped, and lady-shaped, with the anus and reproductive foramen at the end of the worm. Females mature and lay eggs, and the eggs are in the yellow-brown colloidal egg sac outside the genital forehole at the end of the worm, and each female can generally lay 200 to 500 eggs. The male spindle-shaped, linear, roundworm-like, blunt and rounded tail end, slightly pointed front end, male reproductive system, tail end with 1 pair of mating spines, no mating.
Nematodes overwinter in the roots or soil with eggs in the egg sac and 2nd instar larvae, and some overwinter in the roots in different insect forms. Diseased soils and diseased roots became a source of infection at the beginning of the second year. Disease-susceptible seedlings or rootstocks are sources of long-distance transmission. The temperature rises in the early spring of the following year, when the new root system of kiwi fruit begins to develop, the eggs in the egg sac begin to hatch, and the hatched 2-year-old larvae move in the soil, waiting for the opportunity to invade the new roots, staying in the soil for several days before invading the roots. The distribution of nematodes in the soil is roughly the same as that of roots, and after invading the roots, they develop into 3rd, 4th and mature females and males, and the eggs of the females are laid out in the egg sacs exposed outside the roots, and the females die. This is repeated until early or late November, when the roots enter a dormant period and the nematodes overwinter. There is overlap between nematodes generations.
The length of the life history of kiwi root-knot nematodes is greatly affected by temperature, the low temperature life cycle is long, the temperature is high, the life cycle is short, and the algebra of root-knot nematodes is not exactly the same everywhere due to differences in climate.
The activity, infestation and development of root-knot nematodes are affected by soil temperature and humidity, soil temperature below 10 °C and above 30 °C affects the infestation and development of 2-year-old larvae, and soil temperature below 30 °C above 25 °C is the most suitable for the development of nematodes. Soil that is too wet or too dry is not conducive to the activity and development of nematodes, and the soil moisture content of 60% to 80% is the most suitable. Generally, as long as the soil moisture is suitable for the growth of kiwifruit, then this humidity is also suitable for the activity of nematodes. Continuous flooding inhibits the development and infestation of nematodes, but does not kill all nematodes.
Sandy soils are more severely affected than cohesive soils; in kiwi orchards where the disease occurs in a long age, the incidence of root-knot nematode disease is serious; on the contrary, orchards with a small number of root knots on the root system and short planting age have a mild incidence. Kiwi orchards converted from rice paddies have the lowest incidence of root-knot nematode disease. In addition, the root infested roots of root knot nematodes and the wounds caused by them are conducive to the invasion of Phytophthora, Fusarium and Filigree bacteria, thereby aggravating the occurrence of diseases.
Severely damaged roots are infected with root-knot nematodes
1. Strict quarantine system
It is strictly forbidden to introduce diseased seedlings into disease-free areas, and seedlings infected with rhizoma nematode disease should not be planted. This is an important measure for the control of root-knot nematode disease.
2. Disinfect the mildly ill seedlings
Seedlings infected with a very small number of root-knot nematodes, first cut off the root knots on the diseased roots, and then disinfect the seedlings for insecticidal treatment, soak them in hot water of 44 to 46 ° C for 5 minutes, or soak them with gram line phosphorus or gram line dan nervide of 1% active ingredient for 1 hour.
Seedlings disinfection and root impregnation treatment
3. Soil disinfection
For orchards with severe root-knot nematode disease, according to the occurrence law of local nematode disease, at the peak of overwintering egg hatching, on the eve of invading new roots, use 10% g of line phosphorus granules per mu, or 3 kg of octyl thiophosphorus, or 5 kg of root line phosphorus mixed with 30 kg of fine soil in the garden, and then shallow tillage. If the humidity is not enough, the appropriate amount of water is irrigated, and the prevention and control effect is better. Or apply 100 g of octyl thiophos to the rhizosphere per plant. Or irrigate with 1.8% avermectin emulsion 1000 times solution.
Soil disinfection prevention
4. Increase the application of organic fertilizer and cover the orchard with grass
Organic fertilizer humus decomposition process will secrete some substances, which is not good for nematodes, including fungi, bacteria and carnivorous nematodes that catch nematodes, especially a large number of saprophytic nematodes in the orchard rotting grass after grass covering, which can prey on root-knot nematodes and play a biological control role, thereby reducing the density of the insect mouth of root-knot nematodes.
Essentially, the root-knot nematode of kiwifruit is a pest, but it is too small to be seen with the naked eye, and it will be very obvious if viewed with a microscope. It is precisely because of this insect infestation that the root system will be easily infected with other diseases, so it is also called root-knot nematode disease. In fact, whether it is an insect pest or a disease, as long as the prevention and control method is found, targeted preventive measures will achieve a multiplier effect with half the effort.