One is the root rot of Chinese onion caused by soil problems.
After planting Chinese onion or Liliaceae crops in the same field for many years, the demand for nutrients of these crops is biased. In the long run, some nutrients will be lacking, and unreasonable fertilization and field management will cause a series of problems such as soil hardening and acidification, which is what we call continuous cropping obstacles or continuous cropping obstacles.
Prevention and control measures: rotation planting, re-application of high-quality decomposed farm manure or commercial organic fertilizer, and adding some biological bacterial manure to improve the soil if possible can improve the soil and naturally reduce root diseases.
Second, root rot of scallion caused by pests and diseases.
Root rot of Chinese onion caused by pests and diseases mainly includes root rot, soft rot, root maggot disease and so on.
1. Root rot of Chinese onion caused by root rot
Root rot is a fungal disease, and both soil and seeds may carry germs. Continuous cropping is the main factor causing root rot of Chinese onion, which may cause the occurrence and spread of root rot under high temperature and rainy conditions.
① Symptoms of root rot of scallion.
Root rot mainly harms Chinese onion seedlings and can also occur in adulthood. At the initial stage of the disease, the lateral roots and fibrous roots develop first, and will gradually expand to the main roots with the aggravation of the disease. There were no obvious symptoms at the initial stage of the disease, but with the aggravation of root rot, the new leaves showed yellow symptoms, and in the later stage, the whole leaves turned yellow and withered, and the root bark browned until it rotted, and finally the whole plant died without odor.
② Control measures of root rot
Rotation with non-onion and garlic vegetables; Pay attention to timely drainage after rain; Fill the roots with metalaxyl manganese and zinc, and then cultivate the soil. After cultivating the soil, if the diseased plants are found, the ridges should be opened in time, and the roots should be irrigated with Plich or hymexazol for 2~3 times.
2. Rotten roots caused by soft rot
Soft rot of scallion is a bacterial disease, which is more serious in continuous cropping, low terrain, overgrowth of plants and serious underground pests.
① Symptoms of soft rot of scallion.
Soft rot of scallion mostly occurs in the bulb expansion period. At the initial stage of the disease, the infection usually starts from the wound caused by the root maggot at the base of the pseudostem. The diseased part is soaked in water and rotten, translucent, and some diseased pseudostems are rotten and have an orange-red smell. Dirty white bacteria can be observed overflowing, the leaves are twisted and the plants are lodging.
② Control measures of soft rot
Establish a rotation system to reduce the accumulation of pathogenic bacteria; For plots with serious diseases in successive years, 50 kg of quicklime or 1~2 kg of Pinus elliottii can be sprayed per mu to disinfect the soil; At the beginning of the disease, kocide or streptomycin sulfate can be sprayed. When spraying, pay attention to spraying the base, or irrigate the roots with the above chemicals, every 7~ 10 day 1 time, 2~3 times in a row.
3. Rotten roots caused by onion flies
Onion fly is also called seed fly, and its larva is also called root maggot or ground maggot, which is a kind of pest.
① Symptoms of root rot caused by onion flies.
Damage the root system first, and then eat the fake stem. After the root maggot is damaged, it is uneven, rotten and smelly, which leads to the yellowing of leaves, the whole plant stops growing and even dies. They prefer immature fertilizers and rotten onions and garlic.
(2), onion fly prevention measures
Apply fully decomposed organic fertilizer; Fields with serious damage by larvae can inhibit the activity of root maggots or drown some larvae by flooding; After harvest, some pupae freeze to death when plowing in winter; Before planting onion seedlings, dip the roots with phoxim. When dipping the roots, ensure that the roots are submerged by liquid medicine for 30 minutes, and then take them out to dry and plant. For fields with pests, phoxim, methyl isofenphos or deltamethrin can be used to irrigate the roots.
The third is the rotten roots caused by improper field management.
Improper field management is mainly due to soil water accumulation or high temperature weather after flooding, which leads to physiological diseases of Welsh onion roots.
(1), symptoms of scallion retting roots
After retting the roots, the tissues in the roots of Welsh onion turn brown and rot, the roots gradually die, and the dry-pointed yellow leaves appear on the aboveground parts, which then shrink, eventually leading to the death of seedlings and trees of Welsh onion.
(2) Preventive measures for green onion retting.
Choose high-lying plots to facilitate irrigation and drainage; Pay attention to drainage after rain, and flood irrigation is strictly prohibited; For plots with slightly retted roots, intertillage should be done in time to increase soil permeability, and then they should be transferred to normal management after new roots grow.
It can be seen from the causes of root rot of Chinese onion that although there are many factors causing root rot of Chinese onion, the symptoms of each root rot are different. Therefore, after the occurrence of root rot, it is necessary to find out the cause of the problem by combining planting management methods with the symptoms of root rot, and then implement control measures.