Cabbage Root Fly

The cabbage will be OK to eat. Other cabbages may well be affected, you can safely plant crops there, including cabbages if you want to. Any maggots in the soil will have perished because you removed their food supply i.e. the cabbage roots.

To combat cabbage root fly you must understand its lifecycle. By exploiting a weak point there is a very simple way of preventing damage.

A cabbage root fly is similar to a housefly. It lays its eggs on soil near the base of a cabbage plant. When they hatch the maggots crawl into the soil and feed on the roots. If there are only one or two of them they do little harm. if, as you have experienced, there are dozens of them they will weaken and kill the plant. When the maggots are mature they pupate in the soil and then hatch. So the life cycle begins again.

To prevent them simply fit a disc of material round the stem of each plant flat on the soil. The cabbage root fly lays its eggs on the disc but the maggot is unable to wriggle into the soil and perishes.

You can buy discs but you can easily make them yourself out of anything to hand that will lie flat and stay put like roofing felt, thick plastic sheet, cardboard etc. They should be about 4 inches diameter. Cut a slit to the centre to allow the disc to be fitted. Make a pencil sized hole at the centre to allow the disc to fit snugly round the stem. Water your plants in and fit immediately.