Saddle gall midge

A sporadic pest, saddle gall midge can reduce cereal yields through larval feeding and weakened stems.

Saddle gall midge

Pest

Haplodiplosis marginata

Crops affected

Cereals

Life cycle, identification and symptoms

From April onwards, saddle gall midge larvae pupate in the soil. The time of adult emergence is influenced by soil temperature and moisture. In warm weather, emergence can occur as early as mid-April and can continue for up to ten weeks.

Adult midges are red and up to 5 mm long (females tend to be bigger than males). After mating, females lay blood-red eggs (up to 250) on the upper and lower surfaces of cereal and grass leaves, arranged in rafts along the leaf veins.

Eggs hatch within 1–2 weeks. The newly hatched larvae are white or pale orange, turning to bright orange as they mature.

The larvae move down the leaves to feed on the stem underneath the leaf sheath, causing the formation of characteristic saddle-shaped galls or uneven contours on the stem surface. These symptoms, which are often covered by the leaf sheath, occur mainly on the top three internodes but may occur on lower internodes in backward crops.

Once larvae achieve maturity in July, they drop to the soil and overwinter until the following spring.

Importance

Saddle gall midge usually persists at low population levels and is only a sporadic pest of cereals. In 2010 and 2011, local epidemics were reported in central England, particularly in continuous cropping or tight cereal rotations. Larval feeding can reduce yield. Gall-weakened stems may also lodge.

Risk factors

  • If conditions are unsuitable for pupation (i.e. very dry), larvae can survive in the soil for several years  This can allow pest numbers to build up
  • Grass weeds, particularly couch grass, can act as alternate hosts
  • Heavy soils are associated with the largest populations
  • The risk of crop damage is dependent on the number of adults emerged and the timing of emergence, rather than the number of larvae in the soil
  • Warm and damp soil conditions are ideal for adult emergence
  • Adults do not fly far, unless caught up in strong winds
  • When larval feeding coincides with stem extension (GS31–39) crops are at the highest risk. This occurs most often in late-sown winter wheat and winter barley, and spring-sown cereal crops
  • Although eggs are laid on oats, very few larvae survive after hatching

Management

Monitoring and treatment thresholds

To help indicate when adult midges are likely to emerge, take regular soil samples and wet sieve them to reveal the pest’s developmental stage(s).

During stem extension, position traps at ear height in the crop to monitor adult midge activity. Pheromone traps are the most effective. Yellow water traps can also be used, although correct midge identification is essential.

There are no pesticide label recommendations for the control of saddle gall midge in the UK. Research has shown that any approved insecticide must be targeted at adult midges. Once the larvae have crawled under the leaf sheath, they are difficult to control.

Cultural control

Introducing non-cereal break crops into the rotation may have a significant impact on the level of damage over the whole farm.

Early sowing cereals (in September) can reduce the risk of damage.

Oats can act as a trap crop, because they attract egg-laying females but few larvae survive.

Biological control

Soil-inhabiting predators, such as carabid beetles, staphylinid beetles and spiders, consume larvae and may give some control.

An entomopathogenic fungus, Lecanicillium spp., can affect the larvae viability. Some evidence of control by parasitoids has been recorded in Germany.