What harm do corn aphids cause, and what insecticides are good for controlling them?

Aphids are distributed very widely around the world, mainly concentrated in temperate regions, and are one of the most destructive pests on Earth, damaging most crops, with their destructiveness being relatively obvious on corn. So, what harm do corn aphids cause to corn? What insecticide is used for control?

1. What harm do corn aphids cause to corn?

Corn aphids depend on ants in corn fields for their survival. In winter the eggs are stored by ants in their nests; in spring the ants move the eggs onto grass roots, and they then move to corn roots. Adult aphids and nymphs gather in the heart leaves during the corn seedling stage to cause damage, and after tasseling they damage the ear, sucking sap, hindering growth, and they can also transmit various grass-family cereal viruses. As the plant grows, they concentrate on newly emerged leaves to cause damage. During the booting stage they mostly gather densely inside the flag leaf and on the leaf sheath to cause damage, sucking corn sap while excreting large amounts of honeydew; the honeydew covering the leaf surface affects photosynthesis and easily leads to mold parasitism. The damaged plants become weak, grow poorly, and yield declines.

2. What insecticide is used to control corn aphids?

1. Chemical control

(1) Seed dressing with insecticides

Coating with 70% thiamethoxam seed treatment agent, or seed dressing with 10% imidacloprid wettable powder, gives relatively good control of aphids at the seedling stage;

(2) Using granules

At the corn heart-leaf stage, before aphids break out, apply 1.5-2 kg of 3% phoxim granules per mu into the heart leaves, or apply 300-500 g of 15% chlorpyrifos granules per mu, mixed with fine sandy soil at a ratio of 1:30-40 and spread evenly into the heart leaves, which also controls corn borers;

(3) Spray control

The seedling stage and the early tasseling stage are the key periods for controlling corn aphids. If many aphids are found, choose 10% imidacloprid wettable powder at 1000 times dilution, 10% beta-cypermethrin emulsifiable concentrate at 2000 times dilution, 2.5% cyhalothrin at 2500 times dilution, or 50% pirimicarb wettable powder at 2000 times dilution, 25% thiamethoxam water dispersible granules at 6000 times dilution, etc. for spraying.

2. Agricultural control

Besides using insecticides for control, adopting the wheat-ridge intercropping method for corn cultivation advances the corn by 10—15 days compared with corn sown after wheat, which can avoid the peak period of aphid reproduction and reduce damage. You can also clear weeds in the field and at the field edges in time to ensure ventilation at the planting site. In addition, when planting it is best to plant it in a place with good light; with sufficient light, the chance of aphid infection will be reduced.

3. Natural enemy control

Aphids have many natural enemies, including ladybugs, lacewings, hoverflies and parasitic wasps, which strongly suppress aphids. Apply broad-spectrum pesticides as little as possible, avoid applying pesticides during the peak activity period of natural enemies, and where conditions permit, artificially rear and release aphid natural enemies.

Overall, although aphids are small, their harm should not be underestimated. During cultivation, early detection and early control should be achieved.