**Kohlrabi Root Maggots** (*Delia radicum* and *D. floralis*), often referred to collectively as **Cabbage Root Maggots**, are the destructive larvae of small gray flies. They are one of the most severe pests of root and stem brassicas, including **Kohlrabi**, cabbage, broccoli, cauliflower, and radishes. The flies lay eggs near the base of the plant stem, and the hatching maggots burrow down to feed on the root and stem tissue. This feeding destroys the root system, causing the plant to wilt, turn yellow, and often die entirely.
Taxonomy and Classification
Kohlrabi Root Maggots belong to the order Diptera (true flies), family Anthomyiidae. They undergo complete metamorphosis. The life cycle involves the adult fly emerging in spring and targeting new brassica seedlings. Maggots hatch, feed for several weeks, pupate in the soil, and produce multiple generations per growing season, leading to persistent pest pressure.
Physical Description
Adult flies are small, gray, housefly-like insects, about 1/4 inch long.
- **Larvae (Maggots – Key ID):** Creamy white, legless, tapered maggots, up to 1/3 inch long when mature. They are found exclusively underground, feeding on or tunneling through the root and stem tissue.
- **Eggs:** Tiny, white, elongated eggs, often laid in clusters in the soil near the base of the plant stem.
- **Damage Sign:** Sudden **wilting** (especially in hot sun) of otherwise healthy seedlings, followed by yellowing of the lower leaves and plant collapse. When the plant is pulled up, the root system will be severely damaged, often with visible tunneling and small white maggots present.
Distribution and Habitat
Kohlrabi Root Maggots are widespread in temperate regions globally, particularly in areas with large-scale brassica cultivation. Their habitat is the soil and root systems of the host plants. The adult flies are often seen walking on the soil surface near the plant bases, actively searching for laying sites.
Behavior and Conflict
The conflict is the total loss of the brassica crop.
- **Root Destruction:** The maggots’ feeding completely girdles the root and tunnels into the stem base (or the kohlrabi bulb itself), preventing the plant from taking up water and nutrients.
- **Vulnerability:** Newly transplanted seedlings are the most vulnerable, as their small root system is easily overwhelmed by even a few maggots.
- **Attraction:** The flies are highly attracted to the scent released by brassica roots, making repeated cultivation in the same spot highly prone to infestation.
Management and Prevention
Control is integrated pest management (IPM), relying heavily on physical exclusion and cultural methods.
- Use **floating row covers** (fine mesh) over seedlings and transplants immediately after planting to prevent the adult fly from landing and laying eggs at the base of the plant.
- Install **tar paper or plastic collars** around the base of individual plants at the soil level to physically block the fly from laying eggs on the soil.
- Practice strict **crop rotation**, moving brassica crops far away from where they were grown the previous year.
- Delay planting until early summer to avoid the peak egg-laying period of the first generation.
- For commercial growers, a granular or liquid insecticide may be applied directly to the soil at the base of the plant at planting time to kill the hatching larvae.
Conservation and Research
Kohlrabi Root Maggots are managed as severe vegetable pests. Research focuses on improving the efficacy of soil-based insecticides, developing biological controls (like parasitic wasps), and refining cultural controls such as companion planting and barrier methods.