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CARROT FLY
(Psila rosea)

(This page was originally published on www.nugget.demon.co.uk)

1.  WHAT IS A CARROT FLY?

An adult Carrot Fly is a very small black fly which has been described as "a low flying miniature cruise missile". The fly is reputed to be attracted to the carrots by smell. It lays its eggs in the soil adjacent to the Carrot(s). The grub of the fly over-winters in the ground gorging itself on your carrots, pupates and lays eggs in early spring. Eggs will ideally be laid near to carrots but parsley, cow parsley,celery, (and possibly parsnips), are also liked. After the spring generation have hatched they lay eggs in June and July and this second generation hatches and matures in enough time to have another frenzy of egg laying August/September time.

2.  HOW DO I KNOW MY CARROTS HAVE GOT THE FLY?

Basically you will not know until you lift the crop. In severe infestations the first sign is that the carrot leaves look an orange/reddish/rusty colour. They then turn yellow. On lifting an affected carrot it will be seen that the root end will be black or dark. Close examination of what appear to be good carrots may reveal small holes in the carrot. If carrots are put in a bucket of water badly affected ones will come to the surface. This however does not mean that those which do not float are totally unaffected.

3.  I THINK MY CROP IS AFFECTED. WHAT DO I DO?

Lift the crop. There is no point in leaving them in the ground as all you are doing is giving the Carrot Fly maggot ideal board and lodgings. Give the carrots the bucket of water test and discard any which come to the surface. Of the others you may, with a bit of judicious cutting and scraping, be able to salvage something. Any you consider eatable open freeze for 24 hours, or blanch and freeze, then bag and store.

4.  CAN I PREVENT CARROT FLY ATTACKS?

There are five options you may wish to try...
  1.  Companion planting.
  2.  Prevent the fly getting to the carrots using barriers.
  3.  Apply an insecticide to the soil to prevent eggs hatching.
  4.  Use a fly resistant variety.
  5.  Careful timing.

 

Lets look at the options...

Companion Planting

  4.1.  It is thought that if a screen of strong smelling vegetables is planted around the row(s) of carrots it will deter the fly. onions or garlic are usually used. However Carrots are an all the year crop whereas onion and garlic are usually of sufficient height only for a couple of months of the year. Most gardeners will have lifted their onions and garlic well before the fly is at its most numerous in the early Autumn.
 

You could try the newish spring onions of the Ishikuro type that can be picked at almost any stage from small to leek size.
(gareth@swansea.demon.co.uk).

Barriers

 4.2.  This is a fairly satisfactory method. The author grows his early carrots in a cold frame which is about 28" tall at the rear and 12" tall at the front. A percentage of the crop is affected, (very roughly 10%).
Good Reading (1) suggests building a screen approx 18" high around the carrot rows using stakes and polythene sheeting.

Other suggestions are...
4.2.1.  This year I used fleece on a number of crops - very impressed. If you can bear to have your garden looking like a snowscape, this will give much earlier crops and will protect from most flying insects such as carrot fly and cabbage white butterflies.
(gareth@swansea.demon.co.uk).
 

4.2.2.  I grew carrots under loose agryl fleece with the carrots pushing it up as they grow and I got pretty clean carrots This was in the vale of York where carrot fly is terrible. The only problem was taking it off to weed properly which was a hassle.
(uhba023@rhbnc.ac.uk).
 

4.2.3.  Have you tried growing them under that gauze matting type of thing, it has a name, but I can't remember it. It lets enough light and rain through, but keeps the pesky carrot flies out. It is also used to bring on early crops etc.
(R.C.Dobson@ncl.ac.uk).
 

4.2.4.  Marshalls are selling a new product "Enviromesh" for crop protection. It can be laid over hoops. It's more expensive than fleece (?15.75 for 15ft x 7ft) but is supposed to last at least 5 years.
(mjl@jet.uk).


Suggested Suppliers of Fleeces.
Netlon Ltd,
Kelly Street,
Blackburn,
Lancs.
BB2 4PJ
(01254) 262431
----
Nortene Ltd,
Linenhall House,
Stanley Street,
Chester
CH1 2LR
(01244) 346193
----
Pan Products Ltd.,
Faraday Road,
Aylesbury,
Bucks.
HP19 3RY
The first two I believe do both screens and fleece, the last only ground cover materials.
(rob@mgctech.demon.co.uk).

-----
 4.2.5 Agriframes - (01342)319111   7.95 UKP for 40*5 ft roll.
A local nursery sells it by the metre off a huge roll. I can't remember the price, but it was the cheapest by far and you can get it cut to the length of your beds - overlapping smaller bits is a pain.
(gareth@swansea.demon.co.uk).

Insecticide

4.3.1.  There are a great many brands of insecticide on sale in garden centres and ironmongers. The author spent quite a bit of time in three local centres reading labels and not once did he find the words "carrot fly". It would appear that using chemicals may be a bit hit or miss. However Good Reading (4) suggests the following...
 

When sowing treat the seed drill with diazinon and chlorpyrifos, phoxim, (but see para 4.3.2. below). This will protect the plants for about 6 - 8 weeks. Carrots not to be lifted until the autumn should also be watered thoroughly in late August with spray strength pirimiphos-methylin.
 

4.3.2.  There are few insecticides available to amateur gardeners for the following reasons. Firstly to do the job strong products are needed which are generally too toxic for amateurs to use. Secondly carrots have a habit of accumulating pesticide in the root and therefore only chemicals which are poorly systemic are generally used. Normally the soil is treated and not the Carrot. Thirdly amateur usage often requires different residue trials to be carried out and under EU rules for North Europe only this can cost over 100,000 per product per crop. Minor uses such as carrot fly is unlikely to be supported in the future.
At present only a few products have carrot fly as an approved use.
Chlorophos (PBI) containing diazinon & chlorpyrifos Soil Pest Killer (Miracle) containing pirimiphos-methyl. Both are dusts used at sowing or transplanting. Pirimiphos-methyl (Sybol) drench can be used afterwards but is bound onto organic matter and will not penetrate far into the soil.
Caution...There are no other actives approved for amateur use that I am aware of. Phoxim approvals (Murphy Soil Pest Killer) were revoked in 1994 with a sell out period to the end of 1996 (I believe).
(rob@mgctech.demon.co.uk).

 Fly Resistant Varieties

 4.4.1.  Marshalls sell a variety called Sytan that is claimed to be less attacked by carrot fly than other varieties. In the past 2 years, my experience is that their claim is fully justified. It doesn't taste quite as good as a true Nantes, but is close. I recommend it. Sytan is 1.16 UKP for a medium packet, 1.75 UKP for a large one, but there is also postage - see the catalogue for details.
(nmm1@cam.ac.uk).
  

4.4.2.  The resistant varieties like T&M 'Flyaway' (I think!) are getting quite good press.
(gareth@swansea.demon.co.uk).
 

4.4.3.  Good Reading (5) suggests the quick maturing variety Nandor.

Timing

 4.5. If using fleece or other barrier method the seeds can be sown in February/March and lifted in July leaving clear soil before the major problem of second generation larvae develops.
Secondly delay sowing until early June and sow thinly. The carrots are then quite young at the second generation egg laying time and are less attractive. If sown thinly they will not need to be thinned and therefore not produce the odour of damaged carrot which will really attract the fly. If the carrots are then lifted in October/November (they will be small but relatively uninfested) any remaining larvae are left without a source of food and die over winter.

5. ANYTHING ELSE I CAN DO?

As the fly is reputed to be attracted to carrots by smell it would suggest that care should be taken when harvesting to prevent as far as possible any bruising of foliage. Good spacing may help in this respect. As carrot seed is notoriously difficult to sow perhaps trying pelleted seeds may help. Do not leave foliage lying around. If you have suffered a really bad attack turn over that patch of ground early in the winter. A repeat turning over some weeks later is advisable. Birds/frost may well eat/kill any residual maggots.

HELP !!

Information on the following would be much appreciated:


A...  Any references to trials of fly resistant Carrots.
B...  Supplier(s) and prices of ready made screens.
C...  Should fly ravaged Carrots be composted? Or burnt? Other suggestions?

GOOD READING

(1). Organic Gardening. 1988 version. Author Roy Lacey.
Approved by the Soil Association.
ISBN.0-7153-9175-5

(2). Which? Guide to Pests and Diseases. 1991 version.
ISBN. 0-340-55000-7

(3). Know and Grow Vegetables. 2 paperbacks.
ISBN. 0-19-857547-5 (book 1)   0-19-286017-8 (book 2)
My copy is now quite old, 1979 & 1982. May be out of print.

(4). Garden Pests and Diseases. R.H.S. 1992 version. Soft back.
ISBN. 1-85732-906-6

(5). Which? Guide to Gardening without Chemicals. 1990 version.
ISBN. 0-340-52796-X
Excluding (3) all may be available in your local library.

BROWSING

Royal Horticultural Society.
You may find some reference to pests and diseases.
 

Research Institute for Plant Protection.
Again you may find some reference to pests and diseases.
 

Organic Gardening Site.
Advice on making a screen to put around your Carrots.
 

Washington State University.
Report on intercropping as a means of reducing Carrot Fly attacks.

 


Author's Note:
This FAQ is now some years old and has never previously been updated therefore addresses and prices may well have changed.

My grateful thanks to all those whose advice and suggestions helped to make this FAQ.
Ron Lowe


Version 1.0  July 1996
Version 1.1  April 1999


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