Home vegetable growers often find insects are damaging to their growing plants. Small, white insects in the soil are often root maggots, which are a common vegetable plant pest. Onions, cabbage, rutabaga and carrots are often infested with root maggots. These bugs feed on plant roots, causing reduced vigour and crop loss.
Root maggots are the larval form of flies, which are often found in the soil where vegetables plants grow. These small, white or yellow grubs are 1/3 inch long and have a pointed head capsule. Root maggots place their eggs at the base of vegetable plants, after hatching the larvae feed on plant roots. Heavy infestations of root maggots can kill entire root systems and plants.
Root maggots live in the soil beneath vegetable plant roots, where they feed. Plants with root maggots often appear unhealthy and turn yellow from feeding injuries. Roots of infested plants have brown scars and tunnelling injuries. Vegetable plants may produce reduced crop yields, wilt rapidly and die. Onion and cabbage seedlings are most vulnerable to root maggot infestations. Underground damage to vegetables infested with root maggots may cause root rot, which often causes the vegetable to be inedible, according to the Missouri Botanical Garden.
Preventing flies from laying their eggs on host plants is the key to avoiding root maggot infestations. Placing a barrier, such as agricultural fleece or rock phosphate, around vegetable plants may help reduce egg laying. Placing a collar around young seedlings is another way to prevent root maggot infestations.
Predatory insects naturally control root maggots by feeding on them. Ground beetles, parasitic wasps and green lacewings all feed on larvae, reducing their populations. Tilling the soil after harvest will reduce overwintering in these areas and applying soil-based insecticides may also help reduce root maggot damage.