White grubs are the larvae of scarab "chafer" beetles. They are white, C-shaped with a brown head and 3 pair of legs. Some species of whitegrubs (e.g. Phyllophaga spp, Heteronychus spp.) feed on roots of maize plants. Root damage is manifested by wilting seedlings, poor stands, and patches of tilted or lodged plants showing uneven growth. Injured plants can easily be pulled out of the ground.
Feeding of adults on maize leaves is usually not of economic importance. However, adults of the black maize beetles (Heteronychus spp.) are reported as major pests of cereals in many parts of Africa. They eat the stems of young shoots just below the ground. One adult beetle may destroy several seedlings in a row.
- Remove old plants and weeds before planting.
- Plough and harrow the field to expose eggs and grubs to predators (e.g. ants and birds) and to desiccation by the sun. Once exposed, they can also be picked by hand. This is feasible in small plots.
- Provide conditions for growing healthy plants. They can tolerate grub feeding without serious damage.
- Ensure proper drainage. Grubs love moist soil, especially with decaying organic matter. Female beetles prefer to lay eggs on moist-decaying organic matter.
- Avoid planting maize immediately after old pasture in areas where grubs are frequently seen.
- Practise crop rotation. In particular, in fields where whitegrubs are common.
- Use trap crops and / or repellent plants. Good trap crops are African marigold, sunflower, and castor. Repellents plants are chives, garlic, tansy, and catnip. The crops trap and repel adult beetles from attacking the main crop grown (Golden Harvest Organics, 2003).