Cold dew refers to a period of low-temperature weather characterized by an average daily temperature below 20°C for more than three consecutive days in September. This phenomenon is considered a severe weather condition that significantly affects the late growth stage of double-season late rice. The cold dew wind primarily impacts the heading and flowering stages of the rice, often causing the panicles to remain closed, improper flower opening, and obstacles in pollination and fertilization. As a result, the empty grain rate increases, which can severely reduce the yield.
To minimize the damage caused by cold dew, farmers should not only implement preventive measures such as selecting cold-tolerant rice varieties, appropriately scheduling sowing dates, and cultivating strong seedlings but also closely monitor weather conditions during the heading and flowering periods. Once a cold dew wind is detected, immediate and comprehensive protective measures should be taken:
1. **Flood with deep water for insulation**: Before the arrival of cold dew winds, maintain a water depth of 7 to 10 cm to provide insulation. After the cold dew wind subsides, gradually drain the water to avoid root damage.
2. **Apply grass ash**: Spread a certain amount of grass ash 1 to 2 days before the cold dew wind occurs. This helps improve soil temperature and promote healthy plant growth.
3. **Foliar spray of fertilizer**: Two days before the onset of cold dew, apply 200 grams of potassium dihydrogen phosphate or another suitable foliar fertilizer per acre mixed with 75 kg of water. This promotes root, stem, and leaf development, enhances plant vitality, and improves the seed setting rate and 1000-grain weight.
4. **Spray "920" (gibberellin)**: During and after the cold dew period, spray 1 to 2 grams of "920" per 50 kg of water on rice plants that are not heading properly. This can effectively prevent the necking problem in hybrid rice and improve overall productivity.
5. **Control pests and diseases**: After the cold dew wind, some plants may suffer mechanical damage or even fall over, increasing the risk of pest infestations such as rice planthoppers. Therefore, it's essential to monitor for any signs of pests or diseases and take timely action to control them.
By implementing these strategies, farmers can better protect their late rice crops from the adverse effects of cold dew, ensuring healthier plants and higher yields. It's important to stay alert and adapt farming practices based on local weather conditions and crop development stages.
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