Multiple Control of Black spot of Sweet Potato

Sweet potato black spot, also known as sweet potato black scar disease, has become one of the common and serious diseases in sweet potato producing areas in China. According to statistics, the annual production loss caused by the disease in our country is 5% to 10%. The consumption of diseased potatoes by livestock can also cause poisoning, and serious cases die.

First, symptoms can occur in seedling stage, growth period and storage period, which mainly harm potato seedlings and potato pieces, but do not harm the green part. During the storage period, the disease spot on the potato block mostly occurred in the wound and root eye, initially a small black spot, and gradually expanded into a round, oval or irregular plaster-shaped spot, slightly sunken, with a diameter of 1cm to 5cm, and a clear outline. The tissue of the disease department is hard, which can go deep into the potato meat 2mm to 3mm. The potato meat is dark green and bitter. In the later stage of storage, it is often complicated with other fungal and bacterial diseases, resulting in decay.

Second, the comprehensive control strategy should take the disease-free seed potato as the basis, the cultivation of disease-free and strong seedlings as the center, safe storage as the guarantee, and chemical control as the auxiliary comprehensive control measures.

1. Strictly implement the quarantine system. It is strictly forbidden to transfer seed potatoes and seedlings from the disease area.

two。 Choose disease-free seed potato. Disease-free seed potato can be obtained by the following ways and methods.

1) stay in the field without disease. Seedlings, soil and manure are required to be free of bacteria, and attention should be paid to prevent the introduction of germs into agricultural operations. Therefore, it must be done: ① uses high cutting seedlings, soaking seedlings with chemicals, or cutting vines and planting summer potatoes on spring potato vines. ② should choose the growing land that has not been planted for 3 years. The seed potato harvested by ③ should be harvested, transported and stored separately. The means of harvest, transportation and storage cellar should be free of bacteria and can be sterilized if necessary. ④, be careful not to carry bacteria in manure.

2) selection of seed potatoes. After the seed potato comes out of the cellar, the sick, injured and frozen potato pieces should be strictly removed before raising seedlings.

3) safe storage. Seed potato pieces should be harvested in time, frostbite should be strictly prevented, and selected into the cellar to avoid damage. After entering the cellar, the seed potato was treated with high temperature, 35-37 ℃ for 4 days and nights, and the relative humidity was maintained at 90% to promote wound healing and prevent bacterial infection.

3. Cultivate disease-free and strong seedlings.

1) seed potato disinfection. The methods of seed potato disinfection and removal of pathogenic bacteria are as follows: soaking seeds in ① warm soup: pre-soaking potato pieces in 40 ℃ ~ 50 ℃ warm water for 1 minute and soaking seeds in 50 ℃ ~ 54 ℃ warm water for 10 minutes, water temperature and treatment time should be strictly controlled, attention should be paid to the same temperature in upper and lower water, and germination test should be carried out after new varieties are treated. Soaking seeds should be put to bed immediately, and the temperature of seedling bed should not be lower than 20 ℃. Soaking seeds with ② agents: 45% Dysenamine water agent, 70% methyl thiophanate wettable powder, 88% allicin (402antimicrobial agent) can be used to treat seed potatoes.

2) raise seedlings with new seedbed as far as possible. When using the old seedbed, all the old soil should be removed and sterilized by spraying. Apply sterile fertilizer. At the initial stage of seedling cultivation, seed potato can be treated with high temperature to promote the formation of callus cork and prevent bacteria from invading from the wound. The high temperature treatment kept the hotbed for 34 ℃ ~ 38 ℃, then decreased to about 30 ℃, and then decreased to 25 ℃ ~ 28 ℃ after budding. The method of raising seedlings with intermittent high temperature (sudden water and fire) can also be used, that is, before the seed potato goes to bed, pour enough water at one time. After the seed potato went to bed, the temperature was rapidly raised to 34 ℃ ~ 38 ℃ and kept for 4 days, and then the Kang temperature was kept at 28 ℃ ~ 30 ℃. Before pulling out the seedlings, the temperature decreased to 20 ℃ ~ 22 ℃. After that, the seedlings were fully watered every time they were pulled out, and the temperature was raised to 28 ℃ ~ 30 ℃. High shearing seedlings were carried out to obtain potato seedlings with or without bacteria. The spring potato seedlings on the seedbed (Kang) should be cut and planted 3-6 cm from the ground. Plant the cut seedlings in places with good water and fertilizer conditions, strengthen fertilizer and water management, and then cut them 10-15 cm from the ground and plant them in the field, which is the second high-cut seedlings. In some places, cutting potato seedlings from spring potato fields and planting summer potatoes is also a disease prevention measure of high cutting seedlings. In the process of raising seedlings, the method of spraying bed and soaking seedlings can be used to control black spot. Drugs are: 70% or 50% methyl thiophanate wettable powder. When soaking the seedlings, the solution is required to soak to about 10 cm at the base of the seedlings.

4. Disease resistant varieties were selected.

5. Strengthen cultivation management. Implement crop rotation, increase the application of organic fertilizer without disease residue, and control underground pests in time.