Cabbage root maggots, or Delia radicum, are potentially ruinous cool-season pests that enjoy feeding on the roots of plants ranging from cabbages to radishes. They can be hard to spot without digging and harder still to eject from your garden, but there are a number of organic and conventional prevention and treatment techniques that can help you save your crop.
Cabbage root maggots are the larvae of the cabbage root flies, which lay their eggs near the stem and soil around young plants in early spring.
Because the maggots themselves feed under the soil, your first sign of infestation usually won’t be a root maggot sighting. Instead, you’ll see wilting leaves that may display a bit of discoloration. Eventually, the entire plant will likely stop growing and die.
While no method is a 100-percent effective means of keeping root maggots (or root flies) at bay, there are a few ways to lower your chances of an uncontrollable infestation.
Since cabbage root flies will usually sow their eggs in early spring, one of the easiest ways to prevent initial exposure is by waiting until late spring or early summer to transplant.
Using row covers prevents initial exposure by keeping the root flies from planting their eggs on your young plants. The technique is much less effective when a prior infestation has happened in the same garden bed, as the overwintering maggots can work their way back up from the soil.
This works as both an initial preventative technique and to prevent re-establishment of root maggots in future seasons. Rotate susceptible crops so that they don’t sit in the same bed more often than every three years.
If you already have root maggots, all is not lost—although the pesticide-based control methods are admittedly more effective than the organic ones. If you want to try organic first, though, there are a few ways to go about it.
Nematodes are also an effective maggot control method in many areas and can be purchased for home use.
The sole “conventional”, or inorganic, way to control a cabbage root maggot population is through pesticides. These are more effective than the organic methods by far. Because root maggots live primarily under the soil, most pesticides will need to be spread with a thorough watering to help the pesticides soak in.