Contarinia nasturtii, the swede midge, is a small fly, the larvae of which infest brassica plants, causing twisting and distortion of the leaf stems and foliage including death of the growing point in seedlings, or damage to developing flower heads.

During this time the female lays about one hundred eggs in several batches on the leaves of suitable host plants.

[2] Host plants for the swede midge include cauliflower, broccoli, cabbage, Brussels sprouts, kohlrabi and a number of wild plants in the brassica family including shepherd's purse, field penny-cress, field peppergrass and yellow rocket.

If the infection occurs in the flowering stage of cauliflower, it causes a stunted, multi-branched, tuft-like appearance of the flower-head.

It was first detected in Canada in 1996 and is now present in Ontario, Quebec, Nova Scotia and Prince Edward Island.