What are the multiple control methods for sweet potato black spot disease

Sweet potato black spot disease, also known as sweet potato black scar disease, has become one of the most widespread and serious diseases in sweet potato producing areas of China. According to statistics, the annual yield loss caused by this disease in China is 5%-10%, and livestock eating diseased tubers can also cause poisoning, with severe cases leading to death.

I. Symptoms It can occur at the seedling stage, growth stage and storage stage, mainly harming sweet potato seedlings and tubers, but not the green parts. During storage, the lesions on tubers mostly occur on wounds and root eyes, initially as small black dots, gradually expanding into round, oval or irregular plaster-like lesions, slightly sunken, with a diameter ranging from 1-5 cm, with clear outlines. The diseased tissue is hard, can extend 2-3 mm into the tuber flesh, and the tuber flesh is dark green and bitter in taste. In the later storage period, it often occurs together with other fungal and bacterial diseases, causing rot.

II. Integrated control The control strategy should adopt integrated control measures based on disease-free seed tubers, centered on cultivating disease-free strong seedlings, with safe storage as the guarantee, and chemical control as an auxiliary measure.

1. Strictly implement the quarantine system. It is strictly forbidden to transfer seed tubers and seed seedlings from diseased areas.

2. Select disease-free seed tubers. The following routes and methods can be used to obtain disease-free seed tubers.

1) Disease-free seed production field. It is required that seedlings, soil and manure do not carry the pathogen, and attention should be paid to preventing the introduction of the pathogen through farming operations. Therefore, the following must be done: ① Use high-cut seedlings, combined with dipping seedlings in chemicals, or cut vines from spring sweet potato vines and plant them as summer sweet potatoes. ② The seed production field should be selected from land where sweet potatoes have not been planted for 3 years. ③ Seed tubers harvested from the seed production field must be harvested, transported and stored separately, and the harvesting and transport tools and storage cellars should not carry the pathogen; chemical disinfection can be used when necessary. ④ Be careful that manure does not carry the pathogen.

2) Carefully select seed tubers. After the seed tubers are taken out of the cellar, diseased, injured and frost-damaged tubers must be strictly removed before raising seedlings.

3) Safe storage. Seed tubers should be harvested at the right time, strictly protected from frost injury, carefully selected and put into the cellar, and damage should be avoided. After the seed tubers are put into the cellar, high-temperature treatment should be carried out at 35-37 °C for 4 days and nights, with relative humidity maintained at 90%, to promote wound healing and prevent pathogen infection.

3. Cultivate disease-free strong seedlings.

1) Disinfection of seed tubers. Carry out disinfection of seed tubers to remove the carried pathogen. The methods are: ① Hot water seed soaking: after pre-soaking the tubers in warm water at 40 °C-50 °C for 1-2 minutes, transfer them into warm water at 50 °C-54 °C and soak for 10 minutes. The water temperature and treatment time must be strictly controlled, and care should be taken that the water temperature at the top and bottom is consistent. After treatment of new varieties, a germination test should be carried out. After soaking, the tubers should be immediately placed on the seedbed for sowing, and the seedbed temperature must not be lower than 20 °C. ② Chemical seed soaking: 45% amobam aqueous solution, 70% thiophanate-methyl wettable powder, 88% ethylicin (402 antibacterial agent), etc. can be used for chemical treatment of seed tubers.

2) Use new seedbeds for raising seedlings as much as possible. When using old seedbeds, all the old soil should be removed and disinfected by spraying. Apply sterile fertilizer. In the early stage of seedling raising, high-temperature treatment of seed tubers can be used to promote the formation of suberized callus tissue and prevent the pathogen from invading through wounds. High-temperature treatment means that after the seed tubers are placed on the seedbed for seedling raising, the hotbed is kept at 34 °C-38 °C, then lowered to about 30 °C, and after sprouting lowered to 25 °C-28 °C. An intermittent high-temperature (alternating watering and heating) seedling raising method can also be used, that is, before the seed tubers are placed on the seedbed, water thoroughly once. After the seed tubers are placed on the seedbed, the temperature is quickly raised to 34 °C-38 °C and maintained for 4 days, after which the bed temperature is maintained at 28 °C-30 °C. Before pulling seedlings, lower the temperature to 20 °C-22 °C. After that, each time seedlings are pulled, water thoroughly once and raise the temperature to 28 °C-30 °C. Implement high-cut seedlings to obtain seedlings that do not carry the pathogen or carry little of it. For spring sweet potato seedlings on the seedbed (heated bed), cut the seedlings 3-6 cm above the ground for planting. The cut seedlings are then planted densely in a place with good water and fertilizer conditions, with strengthened fertilizer and water management, and then cut high again 10-15 cm above the ground and planted in the field; this is the second high cutting of seedlings. In some places, cutting sweet potato vines from spring sweet potato fields to plant summer sweet potatoes is also a disease-preventing measure of high cutting of seedlings. During the seedling raising process, the methods of spraying the bed with chemicals and dipping seedlings in chemicals can be used to control black spot disease. The chemicals include: 70% or 50% thiophanate-methyl wettable powder. When dipping seedlings, the chemical solution should be required to soak about 10 cm of the base of the seedlings.

4. Select disease-resistant varieties.

5. Strengthen cultivation management. Implement crop rotation, apply more organic fertilizer that does not contain diseased residues, and control underground pests in a timely manner.