Cabbage Maggot

Host Plants

The cabbage root maggot is a destructive pest of cruciferous crops, such as cabbage, broccoli, cauliflower, and other members of the Brassica family. In addition to these crops, the cabbage root maggot can also infest other plants in the family, such as radishes, turnips, and rutabagas.

Regions impacted

The cabbage root maggot is found worldwide, especially in regions with cool climates, where the growing season is short, and the temperatures are cool.

Description

Delia radicum, also known as the cabbage root fly, is a small, gray fly. The adult fly is approximately 3/16 inch to  1/4 inch (5-7 mm) in length, with grayish-black wings and a shiny black head. The larvae, or maggots, are cream-colored and legless, with a pointed head and a cylindrical body.

The cabbage root fly lays its eggs near the base of the plant, and the larvae hatch and burrow into the plant’s roots, causing significant damage and reducing the growth and yield of the crop. The larvae feed on the plant’s roots, causing the plant to become stunted, yellow, and wilted.

Life Cycle

The life cycle of the cabbage root fly consists of four stages: egg, larva, pupa, and adult.

• Egg: The female fly lays eggs near the base of the plant, usually in the soil or on plant debris. The eggs are small, white, and oval-shaped, and they hatch in 5-10 days.
• Larva: The larvae, or maggots, hatch from the eggs and burrow into the plant’s roots, where they feed and grow. They feed on the plant’s roots for approximately 2-3 weeks, causing significant damage to the plant.
• Pupa: After feeding, the larvae pupate in the soil, forming a pupal case. The pupal stage lasts for approximately 7-10 days.
• Adult: The adult fly emerges from the pupal case and mates. The female lays eggs, starting the cycle over again. There are several generations of cabbage root flies each year, with the exact number depending on the climate and growing conditions.

It is important to monitor the presence of the cabbage root fly and implement control measures when necessary to reduce the damage it causes to crops and support the health of your garden. By understanding its life cycle, you can better predict and prevent the impact of this destructive pest.

Damage and Detection

Detection of the cabbage root fly can be challenging, as the larvae are concealed within the soil and roots of the plant. However, there are several signs that can indicate an infestation:

• Stunted or wilted plants: The larvae feed on the plant’s roots, causing the plant to become stunted, yellow, and wilted.
• Presence of adult flies: Adult flies can be seen flying near the plants or on the soil surface.
• Root damage: The larvae feed on the plant’s roots, causing the roots to become damaged and stunted.
• Pupal cases: The pupal cases of the larvae can be found in the soil near the base of the plant.

Prevention and Control

• Use row covers: Covering seedlings with row covers can help to prevent adult flies from laying their eggs near the base of the plant.
• Plant transplants through slits in barriers: Install barriers around your garden, such as fine mesh or floating row covers. The barriers should be tall enough to completely cover the plants, and they should be anchored to the ground to prevent the flies from accessing the plants. Make slits large enough to accommodate the transplant pots. Plant your transplants through the slits in the barriers, and cover the roots completely with soil. Close the slits, ensuring they are completely sealed to prevent the flies from accessing the plants.
• Uprooting and burying or destroying the roots of crops after harvesting the tops: After the tops of your crops have been harvested, the roots should be removed from the soil. Uproot the roots, removing as much of the root system as possible. Bury the roots deep in the soil or destroy them by burning or composting them. This will help to prevent the pupae from emerging as adult flies, reducing the populations of Delia radicum in your garden.
• Purchase parasitic nematodes: Apply the nematodes to the soil around your crops, following the label instructions carefully. The nematodes will infect the larvae of Delia radicum, killing them and reducing the populations of the pest. Maintain soil moisture, as the nematodes require a moist environment to be effective. Repeat applications of parasitic nematodes every 2-3 weeks, as needed, to maintain their populations and effectiveness.
• Wood Ashes: Sprinkle a thin layer of wood ashes around the base of your crops. The sharp edges of the wood ashes can deter the flies from laying their eggs near the base of the plant.
• Diatomaceous Earth: Sprinkle a thin layer of diatomaceous earth around the base of your crops. The diatomaceous earth will desiccate the larvae of Delia radicum, killing them and reducing the populations of the pest.
• Hot Pepper: Mix hot pepper with water to make a spray and apply it to your crops. The hot pepper will deter the flies from laying their eggs near the base of the plant.
• Companion planting: Choose companion plants that repel Delia radicum, such as garlic, marigolds, radishes, sage, tansy, thyme, or wormwood.
• Practice crop rotation: Planting crops in different areas of your garden each year can help to reduce the populations of Delia radicum, as they will have a harder time finding and infesting the new crops.
• Apply insecticides: In severe infestations, insecticides can be used to control Delia radicum populations. However, it is important to choose insecticides that are safe for beneficial insects and the environment and to follow the label instructions carefully.