Swede midge: monitor, detect and control

Swede midge (Contarinia nasturtii) is a small fly whose larvae feed on various members of the brassica family, including many weeds and crops such as cabbage, cauliflower, broccoli, kale, swede and oilseed rape. Find out how to detect and control this pest.

In the UK, swede midge is considered a local and sporadic crop pest. Anecdotal evidence from growers suggests that it is an increasing problem, so AHDB is funding research to find out more.

It occurs mainly in northern Europe, south west Asia, and North America. In North America, it has become a serious issue, causing up to 85% crop losses.

Feeding damage caused by swede midge looks like some other physiological and nutritional problems, so it may have been misdiagnosed in the past.

The larva of the swede midge attacks many types of brassica crop, not just swedes and leads to loss of yield and quality. It is a sporadic pest in the UK. Rate of swede midge development depends on environmental variables such as temperature, humidity and rainfall.

With multiple generations and high reproductive potential, swede midge populations can build up very quickly under continuous production of a host crop.

There are usually three generations in a year. During periods of drought, the larvae may enter a period of dormancy, but development resumes after rainfall.

1. The larvae of the third generation overwinter in the soil.
2. These larvae pupate in the spring, and adults emerge.

Each female lays 60–120 eggs in batches of 15–20 on the younger parts of the plant, particularly the terminal bud. The larvae feed mostly on the growing point but can live on almost any part of the plant.

Detecting swede midge can be challenging, but there are certain methods you can use to spot this pest. From using pheromone traps to looking for plant damage, find out more about the potential methods available.

From cultural control to biological control, effective and consistent management of swede midge depends on an integrated pest management (IPM) approach.