I had a problem with worms in my cabbage and broccoli last year. I also get maggots in my radishes and beets. Is there any way to prevent these?
Yes, you can control worms on cabbage family vegetables and maggots in your root vegetables. Maggots also attack the roots of other plants in the cabbage family including cauliflower, broccoli, turnips, collards, and kohlrabi. Plants can be stunted by these maggots.
Worms in cabbage family vegetables are the larvae of a small moth. Carbaryl (Sevin) is widely used to control vegetable insects. BT, short for Bacillus thuringensis, is an organic pesticide for controlling larvae found under trade names such as Thuricide and Dipel. A new organic pesticide, Spinosad, is also very effective on cabbage worms. All three kill the worms on the plants as they hatch. They need to be applied every two weeks until plants are ready for harvest. Spinosad is only available from full service nurseries and garden stores or on line. You will have to ask for it or check the ingredients label to find it.
The maggots in root vegetables are the larvae of a fly. As soon as plants emerge from the ground after seed planting the flies lay eggs next to the stems. The larvae hatch after a few days and bore into the roots. You can apply pesticide next to the seed before covering and then sprinkle more on top of the soil. Pesticides can be applied in either granular or liquid form. Sevin is available as a dust which can be sprinkled on. If you already have plants up and growing, drench with a liquid application of Sevin or Spinosad.
Diatomaeous earth is a natural pesticide which is very effective on maggots. It must be applied with the seed before the maggot eggs hatch.
Beneficial nematodes will also control root maggots. They are often available from full service nurseries and garden stores or can be purchased on line.
Another good organic approach is to cover susceptible plants with floating row cover. This is a fine mesh plastic fabric which allows 90% of light and moisture through. If tightly closed, row covers prevent the adult flies of maggots and the moths of cabbage worms from reaching susceptible plants.