Carrot fly by csgirla


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									Carrot fly                                                                                              GWF330
                                                                                           Updated February 2009

This pest damages the roots of carrots, parsley, celery, celeriac and parsnips. However,
attacks can be prevented by taking action early in the season.

Q What is carrot fly?                 Q How do I recognise the adult?         the crown of the plant.

A Carrot fly (Psila rosae) is a       A The adult carrot fly is black,
common pest of carrot-family          glossy and 5mm long, with a
                                                                              Q Is there anything I could
                                      yellow head. It’s tricky to             confuse carrot fly with?
crops all over Britain. Carrots are
worst hit, but celery, celeriac,      distinguish from other flies, but is    A Distorted and red-tinged
parsnips, parsley and some other      usually only seen in and around         carrot foliage can also be a
carrot-family herbs are all           carrot-family crops.                    symptom of motley dwarf virus,
attacked by the larvae, which                                                 but the roots are undamaged. It
burrow into the roots. The roots      Q What do plants affected by            is spread by aphids (greenfly).
can be destroyed, killing the         carrot fly look like?
whole plant. Affected roots are
                                      A Carrot plants look stunted and        Q What early warning signs
hard to store, as the wounds left
                                                                              should I look out for?
by the grubs let in diseases such     ‘rusty’. The leaves are small and
as bacterial soft rots and parsnip    develop a reddish tinge, before         A Sadly, the first sign of carrot
cankers.                              turning yellow and dying.               fly you will see is when the plant
                                          In allotments and gardens the       dies or you pull up an infested,
Q When do attacks occur?              plants often die. The carrot fly        damaged root. Commercial
                                      thrives in these habitats as it likes   growers use a trap to detect the
A There are two attacks a year.       sheltering in trees, shrubs and         insects, so they can time their
Where last year’s crops were          hedges. Also allotments tend to         sprays for maximum
infested, the flies overwinter as     be full of carrot-family crops,         effectiveness, but these are not
pupae. The pupae are tiny,            grown closely together year after       available to amateurs. Since the
yellowish cylinders with dark         year, so the flies don’t have far to    pest causes damage every year, it
ends, and their small size and        go to find their host plants.           is worth taking preventative
colour make them hard to spot.            When you pull the roots up,         action before you see any sign of
   The first fly generation           blackened surface tunnels, often        attack.
emerges from May. They lay eggs       containing maggots, can be found
near susceptible plants, which        all over them. Parsnips are             Q Can affected plants be saved?
hatch into white maggots. These       similarly mined by the larvae,
tunnel into the roots and feed        especially the ‘shoulders’ of the       A Once the larvae are inside the
there in mid-summer. They in          root. Young seedlings can be            roots, nothing can control them.
turn pupate and hatch into the        attacked in the leaf stems, as well     Dig up the affected roots to
second generation.                    as the root. This usually kills the     prevent the larvae pupating.
   The second generation then         seedlings. Celery stems are mined       Damaged roots can be eaten, but
lays their eggs. The larvae tunnel    particularly where the stems grow       will tend to rot in storage.
into the roots in the autumn, and     from a crown at soil level. Larvae
sometimes continue to feed all        also tunnel into celeriac roots.        Q Can I re-sow in affected
winter. However, they will all          Parsley is affected by the larvae     sites?
have pupated by late spring, and      killing the thin tap root. If plants
will be ready to hatch.               die, look for mines with larvae in      A Re-sowing where there are still
pupae from a previous crop            leave these unprotected than to       variety to another. In Gardening
guarantees further severe             uncover carrots.                      Which? trials, ‘Fly Away’ was
problems. However, where an               Putting up a ‘fence’ 75cm high    outstanding, though it’s
early crop has to be scrapped         of polythene, fleece or insect-       expensive. ‘Parano’ and ‘Sytan’
before the larvae have pupated,       proof mesh around the plot            also have above-average
it may be safe.                       planted with carrots can also         resistance. However, their
                                      exclude carrot fly. This is because   resistance may need to be
Q Can carrot fly be avoided?          they are weak fliers. Although        supplemented by insecticide or
                                      they can make it over the barrier,
A Sowing thinly and removing                                                barriers if you want to get
                                      they cannot land on to a crop         perfect carrots.
any thinnings immediately
                                      within about 1.8m. Make ‘fenced’
reduces the amount of
infestation. Very early sowing in
                                      enclosures less than this distance    Q Are there any effective
                                      wide or long. Barriers like this      chemicals?
frames, cloches or under fleece
                                      work best in open sites, as carrot
in November or February will let
                                      flies descending from hedges or       A There are no insecticides
the carrots reach a good size by                                            available to gardeners to control
                                      trees can glide in over the
the time the carrot fly is on the                                           this pest.
wing. These early sowings usually
avoid serious damage.
   Alternatively, sowing later,       Q Will crop rotation help?            Q What can I do with affected
after the first generation is over,   A You should always aim to leave
can also avoid damage. If             a break of at least three years       A If the roots are big enough, lift
‘Bangor’ is sown in June, it will     between carrot-family crops in        them as quickly as possible,
grow fast enough to be usable by      the same piece of ground, as          cutting out any damaged areas.
autumn. The second generation         there are soil-borne diseases such
of flies can still cause damage, so   as black rot and sclerotinia that     Q How can I reduce risk to next
early harvesting or covering with     can be controlled by crop             year’s crop?
fleece from September onwards is      rotation. However, although
advisable.                            carrot fly are weak fliers, they
                                                                            A Destroy or bin infected roots
                                      seem able to detect and fly to        before the spring to reduce the
Q What preventative measures          susceptible crops from several        number of carrot flies next year.
can I take?                           miles away, so rotation will not      Do not leave them in the ground.
                                      necessarily help control them.        Digging over the ground in winter
A Barriers of insect-proof mesh                                             rather than in spring may
can exclude the adult carrot flies,                                         increase natural wastage of
if the edges are buried at least      Q Is companion planting               pupae through the effects of
5cm deep. The material can            effective?                            weather and natural enemies.
either be laid over the plants or     A Interplanting onions and carrots
supported on wire or plastic          – six rows of onions to one of        Suppliers of insect-proof
hoops. Fleece does the same job,      carrots is sometimes                  mesh
but it can get very hot under         recommended – is said to confuse
fleece, so insect-proof mesh is a                                           Agralan 01285 860015
                                      the carrot fly by masking the
safer option than fleece for                                      
                                      scent of carrots with the scent of
summer coverings.                     onions. However, the evidence is      DT Brown 0845 1662275
    Put the cover on after the        not yet conclusive. Some herbs
crop has been sown and leave it       such as rosemary are said to have
there until at least the end of                                             The Organic Gardening
                                      the same effect.
June. For total protection leave it                                         Catalogue 0845 130 1304
over the plants for the entire life
of the crop. Parsnips, celery and
                                      Q How good are resistant
                                                                            Ferndale Lodge 0870 4441342
celeriac seem to be less affected                                 
by the second carrot-fly              A There’s a lot of variation in
generation, so it may be safer to     carrot-fly resistance from one

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