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Rape field pests, commonly known as black shell insects or aphids, are a group of pests that include the rapeseed triceratops and coccus beetles. These pests are often found together in the same area, making their identification and management more complex. Among them, there are two main species: the large cocoon beetle and the small cocoon beetle, which can be difficult to distinguish at first glance.
These pests primarily feed on young rapeseed plants and tender leaves, causing significant damage. In the early stages of infestation, seedlings may only have their leaf veins eaten, giving the appearance of being scorched from a distance. The leaves often show numerous holes, and in severe cases, the seedlings may be completely cut off. Infestations tend to be heavier in low-lying and moist areas compared to higher ground. Fields planted later in the season also suffer more than those sown earlier, and flood-prone regions are more vulnerable than hilly areas.
The reasons for the spread of these pests are multifaceted. First, traditional rapeseed farming practices involve high seeding rates, leading to dense canopies and late-developing seedlings—conditions that provide ideal food sources and habitats for the pests. Second, large-scale planting has led to many instances where minor infestations go unnoticed, delaying timely control measures and allowing pest populations to grow. Third, the three types of pests have hidden overwintering sites, making it hard to detect and manage them effectively. Additionally, their hard shells make it difficult for standard insecticides to penetrate, leading to repeated infestations. Their broad habitat range and ability to jump or hide further complicate control efforts. Finally, in some areas, wet weather and mild temperatures in October create favorable conditions for adult reproduction and larval activity, resulting in heavy infestations.
To manage these pests, several strategies can be used. Agricultural control involves clearing stubble and leaves during autumn and winter to reduce the pests' living environment. Traps made from weeds or cabbage can be placed to attract and capture overwintering adults. Chemical seed treatment is another effective method—mixing 5% Ruijin special coating with seeds in a ratio of 1 part Ruijin to 10 parts seed before sowing. Proper fertilization helps strengthen seedlings and improve their resistance by balancing nitrogen, phosphorus, potassium, and trace elements. Transplanting seedlings after spraying with 25% deltamethrin diluted 1000 times can help eliminate invading pests. For chemical control, insecticides with both systemic and stomach action should be used, ensuring even coverage on leaves and the plant’s center. Spraying should be thorough, covering all areas, including weedy patches. Recommended solutions include 50% octanoic acid diluted 800 times, 48% Losben diluted 1000 times, 90% crystal trichlorfon diluted 800 times, 25% deltamethrin diluted 1000 times, or 2.0% rotenone diluted 1000 times. Regular monitoring and timely intervention are essential to prevent outbreaks and protect the crop.