Root Maggots

Maggots seemed like a good topic this close to Halloween, but knowing more about these garden pests can help you protect your plants.

Root maggot fly (Ryan Hodnett) CC BY-SA 4.0

You know that your garden has been infected with root maggots because the roots of many crops will show dark, rotted areas and tunneling. Above ground symptoms look a lot like damping off disease, with wilting, chlorosis and stunting. Heavily infested plants can die.

There are many types of root maggots, but two in particular are frequent visitors to American gardens: the cabbage maggot and the onion maggot. Cabbage maggots (Delia radicum) attack cabbages, broccoli, Brussels sprouts, radishes, turnips, rutabagas and other cruciferous vegetables. And carrots. Onion maggots (Delia antiqua) attack members of the Allium family, including onions, leeks, and chives. 

All root maggots are the larval form of certain species of flies that look like smaller versions of the common house fly. Adults tend to be dark gray with darker stripes on the thorax, but some varieties look more bronze or brown. They are usually about 1/4 inch long and tend to emerge in spring. This can vary, depending on local climate. In warm regions, these pests can emerge practically any time of year. ​​

​Adult flies lay 50 to 200 white eggs next to host plants. When the eggs hatch, the little buggers burrow closer and start feeding on root hairs, small roots, and germinating seeds. The root maggots are yellowish-white and less than 1/4 inch in length.There can be several generations each year.

As we all know, flies are attracted to manure and rotting plant material. This causes problems for gardeners because manure and dead plants are what make up valuable, nutrient-rich compost and mulch. So what is a gardener to do? Well, if you have had problems with root maggots in the past, delay planting until the weather heats up a bit. Also, dig compost into the ground, rather than leaving it near the surface. Crop rotation can go a long way toward reducing the negative impact of root maggots. When starting a vulnerable crop in a new location, row covers can be used to prevent adults from laying eggs nearby.

​Do not use row covers in areas that have already been infested because you will simply be creating a Club Med for garden pests, protecting the root maggots and flies from natural predators.​