How to prevent sweet potato storage diseases? These methods are very practical

Safe storage of fresh-eating sweet potatoes over winter and off-season sales bring potato farmers relatively high economic benefits. In the sweet potato-producing areas on the outskirts of Beijing, storing sweet potatoes has become fashionable. 

Fresh potatoes are large in volume, high in water content, tender in tissue, and thin-skinned, easily damaged, susceptible to chilling injury and disease infection, which leads to rot. Sweet potatoes like warmth and fear cold and dampness. During storage, the main sweet potato diseases include black spot disease, soft rot, nematode disease, wet injury and dry injury. The main causes of disease: potato tubers and potato stems carry bacteria, old cellars cause infection, and potato tubers are frozen, waterlogged or wounded. Whether temperature, humidity, air and other environmental factors are well controlled during storage directly affects the preservation quality of potato tubers. Poor handling causes the above sweet potato diseases and brings relatively large economic losses to storers. 

I. Sweet potato diseases 

1) Sweet potato wet injury and dry injury. Wet injury is mainly caused by long-term water accumulation in the field, or water vapor rising in the potato pile, or rain and snow leaking into the cellar and soaking the potato tubers, causing cellar rot. Dry injury is mainly caused by excessively low relative humidity in the cellar, causing physiological shrinkage and decay. Sweet potato oxygen deficiency is mainly caused by higher temperatures in the early stage of cellaring, or loading potatoes too full, or sealing the cellar too early, all of which can cause cellar rot. 

2) Sweet potato soft rot. It mainly occurs on potato tubers during storage. Improper storage will lead to the rapid spread of this disease. After the potato tuber is infected, the external symptoms are not obvious at first, only the potato tuber becomes soft and water-soaked. Soon, abundant cottony mycelium grows on the surface of the potato tuber, with small black particles on it, namely the sporangia of the pathogen. After the skin breaks, yellow juice flows out with a wine aroma. If later invading pathogens enter, it becomes musty, sour and smelly, and later shrinks into a hard block. 

3) Black spot disease. On diseased potato tubers, plaster-like blue-black sunken spots appear and extend deep into the potato flesh, tasting bitter. When moist, a gray mold layer first appears on the spot surface, then black spiny structures appear. Diseased potatoes are unfit for consumption. The storage period is when black spot disease causes heavy damage and large losses. The source of bacteria mainly comes from diseased potato tubers in the field. The pathogen invades potato tubers through wounds caused by transportation. In the early storage period, high temperature and high humidity can promote disease development. Above 15 degrees Celsius, the pathogen develops relatively quickly. 

4) Sweet potato nematodes. They mainly harm potato tubers. Diseased potato symptoms are divided into the pithy core type and the cracked skin type: (1) Pithy core type. Caused by diseased sweet potato seedlings and seed potatoes. Nematodes invade the tuberous roots from the stem. The disease starts from the top of the potato tuber and gradually develops downward or around it. First, the inside of the longitudinal section of the tuberous root shows cotton-like white pithy tracts, and later forms brown pithy tracts, commonly known as "pithy core" and "pithy flesh". Sometimes, although the inside has been destroyed, the outside is no different from healthy ones, only the weight is reduced. (2) Cracked skin type. Nematodes pierce the outer skin with their mouthparts and enter the interior of the tuberous root to cause damage. Early symptoms are not easy to see with the naked eye. At first the outer skin fades, soon turns blue, some are slightly sunken, some have small cracks, and inside there is dry rot alternating brown and white. The two types often occur together. 

II. Disease prevention 

(1) Before storage, use sulfur, formalin or carbendazim to disinfect and sterilize the surroundings and floor of the storage room, and select potato tubers that are disease-free, injury-free and free of insect holes for storage.

(2) The volume of potato tubers should not exceed two-thirds of the storage space.

(3) Control environmental factors such as temperature, humidity and ventilation in the storage room well. The storage period can be artificially divided into three stages. The first 20 days are the early stage, also called the "sweating stage". Due to high outside temperatures and the physiological activities of the potato tubers themselves, respiration is relatively vigorous and a large amount of water is released. Management in this stage should focus on ventilation and moisture dispersion. The middle storage stage is from 20 days onward to February of the following year, and is also the key period for management. The optimum temperature should be maintained at 10-14 degrees Celsius, and the relative humidity at 85%-90%. When the temperature reaches above 15 degrees Celsius, potato tubers are prone to sprouting, reducing commodity quality. However, if the temperature in the storage room remains below 9 degrees Celsius for a long time, chilling injury is likely to occur. The inside of the potato tubers turns brown and black, hard cores form, they remain tough when steamed or boiled, and they have an off odor, and they may also be invaded by low-temperature pathogens. When humidity is too high and reaches saturation (water droplets appear on the potato tubers), black spot disease and soft rot are likely to occur. When humidity is below 80%, potato tubers begin to lose water, the potato skin color darkens, and dry shrinkage and pithy core appear. If the storage room is poorly ventilated for a long time, the carbon dioxide concentration increases, and the potato tubers will rot. After March of the following year is the late storage stage. Outside temperatures gradually rise. The focus in this stage is ventilation and cooling so that the temperature does not exceed 15 degrees Celsius. Temperature and humidity meters should be placed separately in different parts of the storage room, observed regularly, and timely and effective management measures should be taken according to different conditions to achieve the purpose of safe storage.