Carrot fly (Psila rosae)
This small black fly, which only flies low to the ground, lays its eggs around the roots of any of this family of crops, generally from mid-April until the end of May and from mid-July until the end of August, although there may be three generations in some areas.
The maggots emerge about a week later and begin feeding on the roots, smaller ones at first, before moving into the main tap root. They tunnel through the root which turns brown where soil enters the tunnels, either emerging as adults immediately or overwintering.
- In some cases, the leaves take on a reddish tint and growth may be stunted
- Roots are ringed with brown tunnels, often containing the white or cream maggots which are around 1cm long
- The damage caused may allow secondary infections to cause further damage
- Damage is generally most serious in carrots
Prevention & control
- Good crop rotation and removing all traces of the previous season's crop are essential to prevent the larvae overwintering. For the same reason, harvest in the autumn and store rather than leaving in the ground into the cold months.
- It is attracted by the smell of the foliage so sow thinly to avoid thinning or remove any thinnings immediately
- Planting among rows of onions (2-4 rows for every row of carrots) is said to mask the smell.
- Grow resistant varieties, although these may still be affected if the flies have no other choice. Some people therefore grow a sacrificial row of a non-resistant variety alongside
- Fleece or fine mesh will physically prevent access
- A vertical barrier 75cm or higher then the soil or surrounding vegetation can be used to protect small areas (c.1m) as the flies will avoid flying above this
- Avoid sowing when the adults are laying eggs.
- Mulches and earthing up may also reduce damage by both encouraging healthy growth and making access to the soil near the roots more difficult.