How to harvest sweet potatoes at the right time and store them safely?

? (1) Timely and safe harvesting

1. The best harvest time for sweet potatoes

Sweet potato tubers have no clear ripening period and are usually harvested according to the local temperature. Harvesting too early affects fresh tuber yield, while harvesting too late makes them prone to chilling injury and affects storage. Different harvest times produce obvious differences in yield, quality and storability. For different uses and situations, such as clearing the field for the next crop, processing sweet potatoes, fresh eating, or saving seed, the harvest period should be treated separately.

First, look at the temperature: the normal harvest period should begin when the local average daily temperature drops to 15°C and end at 12°C. Generally, harvest before Frost's Descent.

Second, look at the use of the sweet potatoes: 1) Spring sweet potato processing areas mainly use them for drying and starch processing, so they should be harvested from early October to mid-October. During this period, sweet potato yield and drying rate are both relatively high, and the weather is good, which is favorable for processing. 2) If the field needs to be cleared early, harvest can be done in late September, but sweet potato yield decreases by about 10%. 3) Sweet potatoes for seed must be harvested before Frost's Descent (that is, October 23-24), so the sweet potatoes are not affected by chilling injury; harvesting too early with high temperatures makes them prone to disease after being placed in the cellar. For other uses, such as commercial sweet potatoes for fresh eating, early harvest is possible (spring sweet potatoes reach a growth period of 120 days by late August), allowing early marketing with high prices and good returns. Extra-early-maturing varieties such as Sushu No. 8, Anping No. 1, and Yushu No. 10, with 100 days of growth, can be marketed by mid-August for spring sweet potatoes, at 1 yuan per kilogram, with a yield of 2000 kg per mu and an output value of 2000 yuan per mu, and a season of winter vegetables can still be planted.

2. Safe harvesting

(1) When digging, achieve "four gentles" and "five preventions." "Four gentles" means gentle digging, gentle loading, gentle transporting, and gentle placing; "five preventions" means preventing frost damage, preventing rain soaking, preventing overnight storage, preventing bruising, and preventing disease. Harvesting must be done on sunny days, and the sweet potatoes must be placed in the cellar the same day they are harvested.

(2) When loading and transporting, line the baskets with straw to avoid bruising.

? (2) Safe storage

1. Carefully select before putting into the cellar; separate tubers of different varieties and sizes and put them into the cellar separately. Achieve "ten not into the cellar": tubers that are muddy, damaged, diseased, insect-bitten, frost-damaged, rain-soaked, water-soaked, sprouted, green from exposure, or cracked are not allowed into the cellar.

2. Choose a good cellar site: when building a cellar, choose a place that is sheltered from the wind and faces the sun, with high and dry terrain, no wind pocket, hard soil, and a low groundwater level. Various cellar types can be used, such as semi-underground high-temperature small house cellars, improved well cellars, fixed arched large cellars, well cellars, and shed cellars.

3. Chemical treatment of seed tubers: chemical treatment can kill pathogens on the tuber surface and in shallow wounds, playing a role in disease prevention and freshness preservation. However, it has no effect on physiological changes such as low temperature, wet damage, or bruising. Suitable temperature must still be maintained.

(1) Sweet potato freshness-preserving powder is a compound preparation of multiple pesticides, with relatively ideal disease-prevention effects.

(2) 50% carbendazim 300-fold solution. Seed soaking: it is a systemic

fungicide with high efficiency, low toxicity, low residue, and a broad sterilization range, and has good effects on preventing and controlling black spot disease and soft rot.

(3) 70% thiophanate-methyl 500-fold solution. Seed soaking: it is also a high-efficiency, low-toxicity pesticide. Its properties are the same as carbendazim, but its disease-prevention effect is better than carbendazim.

4. Management of the sweet potato cellar: the suitable temperature for tubers during storage is 10-14°C. Below 9°C they are prone to chilling injury; above 15°C respiration is vigorous, consuming large amounts of nutrients and water, causing tuber weight loss; when the temperature is above 16°C, tubers are prone to sprouting and disease development. According to the characteristics of the tubers and weather changes, cellar management is divided into three stages:

(1) Early stage: in the initial period after the tubers are put into the cellar, focus on ventilation, cooling, and moisture removal. Because the outside temperature is high just after being put into the cellar, the tubers have strong respiration and release large amounts of water vapor, carbon dioxide, and heat, causing high temperature and high humidity in the cellar. This creates good conditions for tuber sprouting and disease infection, especially for diseased tubers, as pathogens infect and spread, causing

large-scale tuber rot, commonly known as "cellar burning." If the temperature is suitable, the tubers will only sprout and not rot. Within 30 days after the tubers are put into the cellar (especially within 20 days), frequently pay attention to changes in temperature and humidity in the cellar and adjust them accordingly. In the first 5-7 days after being put into the cellar, to promote wound healing, keep the cellar temperature at 15-18°C, and be careful not to let the cellar temperature rise above 20°C. After 5-7 days, the cellar temperature should be controlled not to exceed 15°C, preferably 12-14°C, and relative humidity should be kept at 85%-90%.

(2) Middle stage: this period refers to from 30 days after the tubers are put into the cellar to around the Beginning of Spring of the following year, focusing on heat preservation and cold prevention. In this stage, the temperature is low, tuber respiration is weak, and heat release is small, making it the period when tubers are most susceptible to chilling injury. Note that when the cellar temperature drops to 12-13°C, begin heat preservation. For example, seal the soil, close doors, windows, and ventilation openings, and cover the tuber pile with dry grass (which also prevents condensed water from soaking the tubers and causing wet damage). If in severe winter the cellar temperature drops to 9-10°C, heat appropriately according to the cellar temperature.

(3) Late stage: from the Beginning of Spring to before removal from the cellar, ventilation and air exchange should be strengthened. During this period, because the temperature gradually rises, but cold waves continue and the weather changes unpredictably, and because the tubers have been stored for a long time, respiration is weak, and resistance is greatly weakened, they cannot withstand large changes in cellar temperature or low-temperature invasion. Therefore, always pay attention to weather changes, adjust doors, windows, and ventilation openings in time, and keep the cellar temperature at 12-14°C and relative humidity not lower than 85%-90%.