When there is a lot of rain, prevent the cotton from drying up
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In 2008, the Hubei Jianghan Plain experienced a sudden and intense rainfall in mid to late August, which led to an early withering phenomenon in some cotton fields. This resulted in a significant drop in cotton production. According to surveys conducted by the author and agricultural experts, approximately 30% to 40% of the cotton fields suffered from this issue, with varying degrees of severity. On average, the dead seedling rate reached 35.9%, and in severe cases, it exceeded 70%. Some plants recovered after the rain but still experienced substantial yield losses. According to data from a typical household survey, cotton fields that were heavily affected saw a short-term reduction in output ranging from 30% to 50%, with the most extreme cases exceeding 70%. To prevent such issues from recurring in our province, we now provide a detailed description of the situation.
I. Symptoms of Early Wilt
The problem was triggered by two consecutive heavy rains on August 15–16 and August 28, with total rainfall exceeding 150 mm. After the rains, some cotton plants showed partial wilting, turning brown and eventually dying. Others wilted from the top down, gradually dying, while some managed to recover but still suffered from reduced yields. Additionally, some plants developed blue discoloration and dryness after wilting.
II. Factors Related to Early Wilt
1. Variety Sensitivity: A survey of 54 local cotton varieties at the Qianjiang Experimental Station revealed that the average dead seedling rate was 39.5%. Among these, 9 varieties had less than 10% mortality (16.6%), 15 varieties had 10%–30% (27.8%), 23 varieties had 30%–70% (42.6%), and 7 varieties had over 70% (12.9%). Under similar conditions, there were significant differences between varieties. Generally, varieties with fewer bolls and longer growth periods had lighter damage, while those with more bolls and pods had heavier losses. Varieties with stronger resistance to yellowing and wilting also showed lower mortality.
2. Topography Influence: Surveys indicated that areas with high groundwater levels (less than 1 meter) and poor drainage had higher rates of plant death.
3. Fertilization Impact: Most farmers applied top-dressing during the flowering period, typically between July 15 and 20, using 20–25 kg of urea per mu. This was not directly linked to early wilt, but insufficient fertilization or excessive application at the wrong time could worsen the condition. In particular, sandy soils with low potassium levels were more vulnerable. Some farmers applied fertilizer too late or in excess, leading to further damage even after recovery. Potassium deficiency was often associated with yellow or red leaf blight, especially in under-fertilized fields.
III. Causes of Early Wilt
Experts concluded that the sudden rainstorms caused premature aging in cotton plants, particularly in susceptible, early-maturing varieties. High groundwater levels and poor drainage were key contributing factors. Excessive urea application before the rains led to high soil concentrations, which prevented proper nutrient uptake and caused root burn. Some plants could recover, but others showed symptoms like yellowing or reddening of leaves. These diseases spread from the top down and were often mistaken for wilting, though no stem discoloration was observed upon cutting.
IV. Prevention and Management Strategies
1. Use Resistant Varieties: Selecting disease-resistant and drought-tolerant varieties is crucial. Local conditions should guide variety choice, with longer-season varieties planted earlier to avoid peak rain periods. For wheat and rapeseed, early-maturing varieties are recommended to prevent yield loss due to late ripening.
2. Improve Drainage: Fields with good drainage systems experienced fewer problems. In areas with high water tables, proper ditching and drainage are essential to prevent waterlogging after rain.
3. Delay Root Aging: The peak period for root development is during the bud and early flowering stages. After flowering, management should focus on maintaining root health and delaying senescence. Avoid deep cultivation, use small amounts of fertilizer, and apply it strategically. Foliar sprays of 2% compound fertilizer every seven days can help reduce root stress.
4. Increase Potassium Application: If potassium levels are low, additional applications should be made. After August, spray 0.3% potassium dihydrogen phosphate every seven days to improve plant resilience.
5. Post-Event Recovery: After early wilt occurs, immediate action is needed. Drain excess water, remove dead plants, and enhance air circulation. For fertilizer-related damage, water the field to dilute soil concentration and promote recovery. Field management should aim to restore healthy growth as quickly as possible.