Key Points
• Gout fly can cuase significant damage to cereal crops, especially in the spring
• Currently there is no product approved for the control of this pest
Introduction
Damage caused by Gout fly, Chlorops pumilionis, depends on plant growth stage when attacked. In spring-sown cereals late-developing, small shoots and tillers become stunted, gouty and fail to produce ears. Advanced crops have larvae feeding down one side of the ear to the uppermost node, checking growth and damaging grain, causing upto 50% yield loss. Autumn-sown cereals produce stunted, gouty shoots and tillers, similar to affected late spring cereal crops, but autumn attacks are often compensated for by subsequent plant growth. Crops of wheat, barley and rye can be attacked but not oats or maize.
Biology
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There are normally two generations per year. Adult flies with distinctive yellow and black markings are present during May and June. They are a small fly about 4 – 5mm long. Females lay one egg on the upper surface of a leaf, often close to the central shoot. Gout fly eggs are normally 3 – 4 mm long, white and cigar-shaped. Eggs will hatch in approximately 7 – 10 days. Larvae burrow in to the centre of the plant and feed for 4 weeks then pupate. Larvae are normally yellowish in colour and pupae brown. Pupation lasts about 5 weeks before a new adult emerges.
The second generation, occurring in August and September, lays eggs on grasses, volunteer cereals and early-sown winter cereals. These larvae move to the base of the plant stem to feed, producing stunted and gouty shoots in winter and early spring. They pupate in spring producing adults again in May.
Drilling spring cereals from late-April onwards, or winter cereals before mid-September, will increase the risk of these crops being attacked by Gout fly. Conversely, drilling spring cereals before mid-April, or winter cereals after mid-September, will put crops outside the most susceptible stages of growth at peak times for egg laying. September emerging winter cereals in high risk areas should be monitored for egg laying towards the end of September and until late October.
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