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Cotton Seed Dressing and Prevention of Cotton Aphid
Cotton aphid is a major pest that affects cotton seedlings, found across the country and particularly prevalent in cotton-growing regions. These pests tend to gather on the underside of leaves and tender shoots, feeding on sap, which damages plant cells and causes leaf curling, stunted growth, and the secretion of honeydew. This honeydew can lead to fungal infections, further reducing photosynthesis and crop yield.
In northern cotton regions, cotton aphids can complete 10–20 generations per year. They begin damaging cotton fields from April to May, attacking young seedlings before reproducing within the field. The peak damage occurs between May and June, with populations declining after mid-June. However, during dry years, their damage can persist longer. Miao Miao typically appears in late June, with activity starting in mid-May through the bud stage, while Fuxi occurs in late July and August, thriving in high temperatures. Heavy rain significantly reduces aphid numbers, making wet or rainy seasons unfavorable for them. Conversely, sunny weather promotes rapid reproduction—Fuxi can complete one generation in 4–5 days, while Miao Miao takes over 10 days. Overlapping generations are common. Cotton aphids thrive at temperatures between 17–24°C and humidity below 70%. Early sowing of cotton increases infestation risk. When cotton is intercropped with wheat, rapeseed, or broad beans, aphid outbreaks tend to be later and less severe.
To manage cotton aphid infestations, two main prevention methods are commonly used:
1. **Seed Treatment**
One effective method is treating seeds with imidacloprid. For example, using 10% imidacloprid EC or WP at 100g per 3–5kg of seeds, or 70% imidacloprid dispersible powder (Weiyuan Fudie) at 15g per 3–5kg of seeds. The insecticide should be dissolved in water and evenly sprayed onto the seeds, then mixed thoroughly and left to sit for more than 24 hours. The longer the soaking time, the better it is for absorption, especially if germination has not yet occurred.
Farmers who use this method often see fewer seedling pests, reducing the need for pesticide sprays during early growth stages. This not only protects the plants but also helps maintain natural predators of aphids. In Qiuqiu County, farmers reported that treated cotton began budding about seven days earlier than untreated crops. Dong Xinghua, a farmer in Jixi, planted cotton using Weiyuan imidacloprid and did not apply any insecticides from April 27 to May 31. “This year I didn’t mix well by hand,†he said, “next year I’ll use a seed mixer to ensure even coverage.†Without treatment, farmers like Chen Fusheng had to spray up to six times, leading to physical exhaustion. Seed treatment not only saves money on pesticides but also reduces labor significantly, proving its importance and necessity.
2. **Chemical Control**
When aphid populations reach control thresholds, specific pesticides should be applied. For example, when the leaf rolling rate reaches 45% on 2–3 leaf cotton plants, with about 4,500 aphids per 100 plants, or 50% leaf rolling with 6,000 aphids per 100 plants, intervention is necessary. In early July, if an average of 680 aphids per plant is observed, or around 200 in late July, it’s time to act. Pesticides such as 5% acetamiprid EC (2,500–4,000 times dilution), 3% acetamiprid ME (1,000–1,500 times), 20% acetamiprid soluble liquid (6,000–8,000 times), 25% imidacloprid WP (6,000 times), or 30% acephate EC (1,000–2,000 times) can be used. Spraying must be thorough and precise to ensure effectiveness.