(1) Rhizoctonia solani
Rhizoctonia solani mainly harms the seedlings of cabbage, Chinese cabbage and celery, and both newly unearthed cotyledon seedlings and large seedlings can be harmed, generally occurring in the middle and late stage of seedling raising. Dark brown lesions appeared at the stem base of susceptible seedlings, which were obviously depressed, and the lesions spread horizontally. After a circle around the stem, the diseased parts of young stems gradually contracted and died.
Rhizoctonia solani can be spread through soil, seeds, organic fertilizer, irrigation water, rain and so on. High temperature and high humidity in seedbed are beneficial to the occurrence and spread of the disease. Poor ventilation of seedbed, excessive growth of seedlings, or high and low soil moisture and insufficient light are all easy to get sick; Sometimes it is easy to get sick at high temperature and dry early.
The control methods of damping-off disease are as follows: first, strict selection of seedbed and application of fully decomposed organic fertilizer. Second, disinfect the seedbed and seeds in the same way as the fruit and vegetable damping-off. Third, strengthen the management of seedbed, timely ventilate, cool and remove moisture, and move seedlings early. Fourthly, chemical control can be sprayed with 600 times solution of 75% chlorothalonil wettable powder and 500 times solution of 70% zineb wettable powder.
(2) Viral diseases
Virus diseases mainly harm vegetable seedlings such as cabbage, cabbage, mustard and lettuce. The heart leaves of infected seedlings show bright veins or leaves lose green, or produce uneven mottles, mostly mosaic, and in severe cases, the heart leaves are deformed. Sometimes there are not obvious brown necrotic spots and flowers and leaves on lettuce and other seedlings.
Viral diseases are mostly caused by virus-carrying seeds or the spread of aphids. The prevention and control methods are as follows: First, disinfect the seeds before sowing, and generally soak the seeds with 1% potassium permanganate or 10% trisodium phosphate for 15 minutes. Second, timely prevention and control of aphids, see the method of prevention and control of aphids in fruits and vegetables; Silver-gray film can also be used to avoid aphids; Mustard vegetables are often raised with mesh. Third, at the initial stage of the disease, 500 times of 20% virus A wettable powder and 500 times of 20% virus spirit can be sprayed once every 10 day for 2 ~ 3 times in a row.
(3) gray mold
Gray mold is an important disease that harms the seedlings of cabbage, lettuce and other crops, and its control method is similar to that of fruit and vegetable gray mold.
(4) Hagen disease
Black root disease is the main disease of cabbage vegetables during seedling raising. The pathogen mainly infects the root and neck of seedlings, and the diseased part turns black or shrinks, and white mold grows on the diseased part when it is wet. A few days after the seedlings were infected, the leaves wilted and dried up until they died.
The pathogen of black root disease overwinters in soil or disease residues, and seeds, farm tools and compost with bacteria can also spread the pathogen. If the soil temperature is too high, the soil is sticky and wet, which is beneficial to the disease.
The control methods of black root disease are as follows: first, choose the field with high and dry terrain and good drainage as the seedbed, and apply fully decomposed organic fertilizer as the base fertilizer. Sowing should be thin and covering soil should not be too thick. Second, strengthen seedling management, pay attention to ventilation, shade should be covered early and uncovered late, and replenish water should be sprinkled less for many times. Third, the seeds and seedbed soil are disinfected. For specific methods, see the fruit and vegetable damping-off disease. Fourthly, chemical control, commonly used chemicals are 75% chlorothalonil wettable powder 600 times solution, 65% zineb wettable powder 600 times solution, 20% methyl-chloropicrin EC 1200 times solution, etc.