Soybean meal is a recurring pest affecting cowpeas during the summer and autumn seasons. The larvae of this pest cause significant damage, making conventional pesticides like trichlorfon and chlorpyrifos less effective. In recent years, the Rugao Plant Protection Station has conducted extensive research on the life cycle and control methods of these larvae in cowpea fields, developing more efficient strategies for pest management. For instance, in 2006–2007, they demonstrated the application of these techniques in vegetable gardens across several towns, achieving a pod damage rate below 10% and an overall locust protection effect exceeding 85%.
The newly hatched larvae primarily feed on flower buds. As they develop into the second instar, they begin to break open the corolla at night and use silk threads to pull together the receptacles, pods, and fruit branches of the affected flowers. During hot weather, cowpea flowers typically open in the morning and close around 10 a.m. The normally closed flower corolla usually falls off at night, and most of the first- to second-instar larvae are dropped along with it. A small portion of the larvae may remain attached to the tender pods or become entangled in the filaments, continuing to harm the flowers.
When the flowers are no longer suitable for feeding, the larvae move to nearby pods or other floral structures. If the larvae reach the third to fifth instar stage while still inside the closed flowers, they can cause severe damage, leading to flower drop and hindering normal growth. However, some flowers remain suspended on the fruit branches due to the filaments, allowing the larvae to continue feeding on them.
Based on these damage patterns, it's crucial to focus on protecting the buds in cowpea cultivation. The "preventing flowers and protecting the locusts" strategy should be implemented, including manual removal of infested parts and chemical control measures. First, manually remove pests by cutting off the silkworms attached to the fruit branches and the corollas that have detached but still stick to the top of the tender pods, preferably in the afternoon without affecting yield. Second, apply chemical treatments such as 1.8% avermectin or 35% octyl pyrophosphate, which have strong penetration and egg-killing effects, sprayed in the morning when the flowers are open. It’s important to spray again within six hours if it rains. This process should start at the beginning of the flowering period and continue every 6–7 days until the flowering season ends.
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