Cotton aphids are a significant pest that affects cotton seedlings, found throughout the country and considered one of the major threats in cotton-growing regions. These pests cluster on the underside of leaves and tender shoots, feeding on plant sap, which damages the cells and causes leaf curling, stunted growth, and the secretion of honeydew. This sticky substance promotes fungal growth and hinders photosynthesis, further weakening the plants.
In northern cotton regions, cotton aphids can complete 10 to 20 generations per year. They begin damaging cotton fields in April and May, attacking young seedlings before reproducing within the fields. The peak damage period occurs from May to June, with populations declining after June, though drought conditions may extend the infestation. Miao Miao typically appears at the end of June, while Fuxi emerges in late July and August, thriving in high temperatures. Heavy rain has a strong inhibitory effect on aphid populations, making wet seasons less favorable for their survival. However, during sunny weather, aphids multiply rapidly—typically completing one generation every 4 to 5 days. In contrast, Miao Miao requires over 10 days for one generation, leading to overlapping life cycles. Cotton aphids thrive in temperatures between 17°C and 24°C with humidity below 70%. Early sowing of cotton can lead to severe infestations, while intercropping with wheat, rapeseed, or broad beans can delay and reduce aphid occurrence.
Two effective prevention methods are commonly used:
1. **Seed Treatment**:
(1) Treating seeds with imidacloprid is an effective approach. For example, using 10% imidacloprid EC or WP at a rate of 100g per 3-5kg of seeds, or Weiyuan Fudie (70% imidacloprid dispersible powder) at 15g per 3-5kg of seeds. The insecticide should be dissolved and evenly sprayed onto the seeds, then mixed thoroughly and left to soak for more than 24 hours. The longer the soaking time, the better the absorption.
(2) Seed treatment significantly reduces seedling pests, minimizing pesticide use during early growth stages. This not only protects the plants but also helps maintain natural predators, allowing them to control aphid populations effectively. Farmers who have used this method report earlier budding and healthier plants. For instance, in Qiuqiu County, farmers observed that treated cotton started budding about seven days earlier than untreated crops. Dong Xinghua, who planted 120 mu of land in Jixi, said he didn’t need to spray any insecticides from April 27th to May 31st after seed treatment. He plans to improve mixing next year for better results. In contrast, neighboring farmer Chen Fusheng had to spray four times by the same date, experiencing physical exhaustion. Seed treatment not only saves costs but also reduces labor, making it a crucial practice for sustainable farming.
2. **Chemical Control**:
Monitoring key indicators is essential. When 2-3 leaf stage cotton shows a 45% leaf rolling rate, with approximately 4,500 aphids per 100 plants, or when 3-leaf stage plants show 50% leaf rolling with around 6,000 aphids per 100 plants, action is needed. For cotton fumonium, if there are 680 aphids per plant in early July or 200 in late July, it’s time to apply pesticides. Effective options include 5% acetamiprid EC diluted 2,500–4,000 times, 3% acetamiprid ME at 1,000–1,500 times, 20% acetamiprid soluble liquid at 6,000–8,000 times, 25% imidacloprid WP at 6,000 times, or 30% acetyl methamidophos EC at 1,000–2,000 times. Spraying should be thorough and targeted to ensure maximum effectiveness.
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