In recent years, corn red spider infestations have become widespread and increasingly destructive. The damage is more severe in spring corn compared to summer corn. These pests also affect cotton and leguminous crops. In areas where corn and cotton are intercropped, corn suffers greater harm than cotton.
The first signs of infestation appear in early July on the lower leaves of corn plants, particularly on the underside of the leaves near the ground. A fine webbing covers the leaf back initially, and then spreads gradually to the middle and upper leaves. The peak of the infestation occurs in mid-to-late July, after which the damage begins to subside.
Infested corn typically experiences a reduction in 1000-grain weight by 30–50 grams. In severe cases, all the leaves turn gray-green, dry up, and die, leading to a loss of about 100 grams per 1000 grains. It's crucial to implement timely pesticide control measures to prevent further losses.
Corn red spiders are known for their strong resistance to conventional insecticides. They often co-occur with other pests and feed on the underside of leaves, making traditional insecticides less effective. Using acaricides combined with systemic insecticides that have good egg-killing properties can yield better results. For example, a 20% dicofol solution diluted at 1000 times is effective against all life stages of the pest, with an efficacy period lasting 5–7 days.
Systemic insecticides like 40% monocrotophos, 40% omethoate, or 50% methamidophos, when diluted at 1000–1500 times, offer longer-lasting control, typically 7–10 days. However, it's important to stop applying these chemicals 20 days before harvest to avoid residue issues. Another option is using 20% double nail emulsion at a dilution of 1000–2000 times, which provides good control.
Spraying 80% dichlorvos at a 1500 times dilution during sunny afternoons can kill adult mites and other pests within an hour, but its effect on eggs is limited. This treatment should be repeated every 3–4 days for continued effectiveness. It's recommended to spray the underside of the leaves directly for maximum impact. Early detection and consistent management are key to reducing crop losses caused by corn red spiders.
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