Identification and management of frit fly in cereals

Frit fly is a pest of cereals (particularly spring oats), grasses and maize. Learn about its life cycle and how to use integrated pest management to reduce risk to crops.

• Cereals sown after grass leys and spring oats are at highest risk of damage
• Crops are most susceptible to damage up to the four-leaf stage. Warm temperatures during this time increase the risk of infestation
• Sowing spring oat crops early or choosing crops that develop rapidly can narrow the period of risk

Scientific name: Oscinella frit

Adults are small (about 1.5 mm long), shiny and black and are active in warm, dry conditions.

Larvae are small, white maggots, about 3 mm long when mature.

Pupae are protected by a reddish-brown casing.

Oct–Apr: Larvae feed in shoots of cereals and grasses and pupate within the plants.

May–Jun: First generation adults emerge and lay eggs on grasses, spring cereals and maize.

May–Jun: Larvae feed within infested plants and pupate.

Jul: Second generation adults emerge and lay eggs beneath oat husks (can lead to serious damage to the ears of spring oats) and grasses.

Jul–Aug: Larvae feed on oat kernels or grasses.

Aug–Sep: Third generation adults lay eggs on grasses in stubble and early winter cereals.

Damage occurs across the year and can affect shoots and grain. This contrasts with wheat bulb fly and yellow cereal fly symptoms, which are generally only seen from early spring.

Damage in cereals is most evident as ‘deadhearts’, whereby the central leaf turns yellow, withers and dies – often falling out completely. This can kill very young plants. Older plants can produce several tillers following the death of the main shoot. If these are invaded, the shoots are weakened, resulting in reduced yield and later-ripening grain. In oats, deadhearts can be mistaken for stem nematode damage.

Spring oats damage may occur prior to ear emergence and lead to blind, withered spikelets. Damage to oat ears is difficult to detect and the blackened, thinned kernels can only be seen by opening the grains. In maize, severe damage shows as ragged leaves, often torn into strips. Mild damage is evident as neat rows of holes across leaves.

Non-chemical control

Later sowing of winter cereals can reduce risk from the third generation of frit fly. Grass leys should be ploughed at least 4 weeks prior to sowing. For spring oats, early sowing reduces the risk of the vulnerable stage of the crop coinciding with egg laying. Encouraging rapid establishment and growth (for example, through rolling) will help to minimise damage.

Natural enemies include spiders, ground beetles, rove beetles, predatory flies and many parasitoid species.

Monitoring

To assess pre-drilling risk in winter cereals, sample grass or stubble for frit fly eggs or larvae before ploughing. However, the main monitoring period is after full emergence (see Thresholds).

Thresholds

If more than 10% of plants are damaged before the four-leaf stage, the crop is at risk.

Insecticide resistance

None known.