International Journal of Aquaculture, 2025, Vol.15, No.4, 208-220 http://www.aquapublisher.com/index.php/ija 214 Agricultural prevention and control measures: including the selection of pest-resistant varieties, cleaning the countryside and reasonable rotation of crops and stubborns. Promoting disease-resistant varieties such as the "Babu Water Chest" that is relatively tolerant to blight, according to the experiment, its incidence rate is reduced by 25.5% compared with local varieties. After harvesting each season, remove the remaining shepherds in the fields in a timely manner, and buried in depth or burn it to eliminate the source of overwintering bacteria. At the same time, the "bacterial land" elimination system was implemented, and water chestnut planting was suspended for 1 to 2 years in severely ill fields, and the planting of dry crops or rice was changed to purify the soil (Khairullah et al., 2020). 6 Optimization of Harvesting and Primary Processing Technology 6.1 Judgment of maturity and optimal harvesting time The harvesting period of water chestnuts varies according to the variety and planting period. Generally, the bulbs mature 120 to 150 days after sowing. From the external morphology, when the foliar stems on the ground are yellow and lofty and the stolon at the base are loose, it indicates that the underground bulbs have fully developed. Traditional experience uses the harvest signal of "seedlings with dry sounds and crisp sounds", that is, pull up the stems and listen to the crisp sounds of breaking, indicating that the water chestnut skin is thick and hard and can be harvested and dug. If harvested too early, the bulbs have not grown enough and the starch accumulation is insufficient, which will affect yield and taste (Zhang et al., 2021); if harvested too late, the bulbs will easily regenerate or rot in the mud, and the bulbs will not be easily found after the upper part of the ground is completely dead. Therefore, it is very important to choose appropriate harvesting. Studies have shown that nutrient accumulation of water chestnuts reaches its peak around one week before full maturity, and at this time, the best balance between yield and quality can be achieved by harvesting. For commercial fresh water chestnuts on the market, they should be dug appropriately in advance to ensure full appearance and bright skin color; for starch processing, they can be harvested a few days later to make the starch content higher (Figure 1) (Chen et al., 2024). In the main production areas in the south, water chestnuts sown in autumn are usually harvested from January to February of the following year, and the weather is cool at this time, which is conducive to storage and transportation. All localities should flexibly determine the harvest period based on local climate and market demand. 6.2 Comparison of artificial and mechanical harvesting methods Traditional water chestnut harvesting is mainly artificial. Usually, the field water is drained first, and the topsoil is turned manually with a hoe or an iron rake, and the bulbs in the mud are turned off the surface, and then the shepherds are picked manually. The advantages of artificial methods are that they are highly adaptable to different soils, have a low damage rate (the damage rate of manual mining is about 5%~10%), and can be selected simultaneously in grading. But the disadvantage is that the labor intensity is extremely high. A skilled worker can only harvest 200 to 300 kilograms of water chestnuts per day, and it needs to bend over and work in the mud for a long time, which is inefficient. With the shortage of rural labor and rising costs, artificial harvesting has become a bottleneck in the development of the water chestnut industry. The demand for mechanical harvesting is becoming increasingly urgent. In recent years, various places have developed various types of water chestnut harvesting machinery: vibration screening excavator, paddy field harvester, and layered harvesting technology. Based on this, enterprises in Guangxi and other places have developed a double-layer shovel harvester: the front shovel pushes the upper layer of mud, and the rear shovel digs out the lower layer of water chestnut-containing soil for screening and separation. 6.3 Standardization of cleaning, brushing and grading processes The main links of water chestnut processing include cleaning, peeling and grading packaging. In the past, it was mostly done by hand, but is currently improving in the direction of standardization and mechanization: the surface of water chestnuts is often covered with soil after harvest, and must be thoroughly cleaned before sale or processing. Nowadays, bubbling cleaning machines or high-pressure spray cleaning lines are mostly used, and water chestnuts are put into batches of water chestnuts into the sink with bubbles and spray devices to roll and
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