Beating the cabbage root fly
There is an excellent method for deterring theroot fly, which attacks cabbages and other brassicas, such as and Brussels sprouts, laying its eggs just where the stem of the plant touches the .
Collect some empty plastic yogurt or cream containers, wash them out and melt holes about 2.5 cm (1”) in diameter in the bottoms with a candle flame. Cut the cartons down to leave the sides about 2.5 cm (1”) long. The cabbage root fly will be unable to see the stem and will move on to lay its eggs elsewhere in the garden and by the time the stem is too large to fit the hole, it will be strong enough to break the carton and make room for itself.
Although there is no equally effective deterrent against the carrot fly, which hunts by scent, the best method is to scatter lawn-mowings thinly between the rows, replacing them as their smell of drying hay wears off.