Cotton aphids, including both adults and nymphs, are commonly found in the cotton buds, leaf axils, and young leaves. These pests feed by piercing and sucking sap, causing severe damage to the plant. The top buds of cotton seedlings may turn black and dry, leading to the cessation of main stem growth and the formation of "headless" seedlings. This can result in the shedding of flowers and bolls, and in severe cases, the plants may fail to set fruit or produce unripe, low-quality bolls, significantly reducing yield and fiber quality.
The insect is known to prefer green areas and flowering plants. High humidity and heavy rainfall create favorable conditions for their proliferation. In late May, they typically migrate from summer hosts into cotton fields, causing infestations. Cotton fields that are newly transplanted, covered with plastic mulch, or under high-water, high-fertilizer, and high-density conditions often create a humid microclimate that promotes the development of these pests.
It's important to note that even Bt cotton, which is resistant to some pests, is not effective against cotton aphids. Therefore, farmers should remain vigilant and take preventive measures.
According to the Cixi Agricultural Monitoring Center, as of May 28, the average plant damage rate reached 28%, with 4 to 7 aphids per 100 plants. Nymphs made up 90% of the population, surpassing the threshold for intervention. All cotton-growing areas should intensify monitoring and implement timely control measures.
To manage the infestation, several pesticides can be used effectively. Options include 50% malathion diluted at 1000–1500 times, 40% chlorpyrifos at 800 times, or 10% imidacloprid sprayed at 1500 times. The treatment should focus on the top of the plant and the leaf axils. Apply the pesticide every 5–7 days, repeating the process 3–4 times for effective control. It is best to spray in the early morning or late evening to avoid high temperatures and maximize effectiveness. Additionally, spraying weeds and shrubs near the ground can help reduce the pest population in surrounding areas.
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