Testing barrier methods for the protection of carrots from the carrot fly (Psila rosae)

RHS project team
Anna Platoni, Ian Waghorn
Warwick Crop Centre, University of Warwick
Start date
01/03/2016 00:00:00
End date
31/12/2016 00:00:00

Carrot; carrot fly; barriers; pest

The problem

Carrot fly is a small dark-bodied fly whose larvae feed on the roots of carrots and other related plants, such as parsnip, parsley, celery and celeriac. Carrot fly larvae can kill seedlings and damage developed carrot roots by tunnelling into them which makes them less aesthetically pleasing and affects storage potential. Severe attacks can leave much of a crop inedible.

Anecdotal evidence suggests that many gardeners are deterred from growing carrots because of this pest. Since 1967, when computerised records began, the RHS has received over 250 member enquiries relating to carrot fly, more than 81% of all carrot pest enquiries. Partially-resistant varieties of carrot are available as well as a nematode biocontrol product but there are no approved chemical treatments available to amateur gardeners.


Carrot fly adults are weak fliers and protecting carrots using barrier fencing is widely recommended to stop the flies laying eggs on the crop. Carrots will be grown in plots with four different types of barrier protection as well as in plots without protection to compare the damage.

The treatments are as follows:

1) Covering with insect-proof netting: a treatment commonly used by home gardeners as the main alternative to barriers.

2) No barrier as a comparison treatment.

3) 60cm: the barrier height most usually recommended for home gardeners

4) 90 cm barrier: the other barrier height available for gardeners to buy. This barrier height has been shown to be partially-effective in larger scale experiments for agriculture.

5) 60cm with an overhang: not usually recommended for home gardeners but may have added value compared to straight barriers as flies scaling the barrier may become trapped under the overhang.

Carrot fly barriers
Carrot fly damage on parsnip


The aim of this project is to determine if barrier methods can be effective in controlling carrot fly in home gardens and, if so, the optimum height and configuration required.

Benefits to gardeners

This research will inform and improve the advice that the RHS can provide in helping gardeners to reduce carrot fly damage.

Further information

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