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Plantwise Technical Factsheet

carrot root fly (Psila rosae)

Host plants / species affected
Anethum graveolens (dill)
Anthriscus cerefolium (chervil)
Apium graveolens (celery)
Apium graveolens var. rapaceum (celeriac)
Brassica
Brassica oleracea var. botrytis (cauliflower)
Carum carvi (caraway)
Conium maculatum (poison hemlock)
Coriandrum sativum (coriander)
Daucus carota (carrot)
Foeniculum vulgare (fennel)
Levisticum officinale (lovage)
Pastinaca sativa (parsnip)
Petroselinum crispum (parsley)
Raphanus sativus (radish)
List of symptoms/signs
Leaves  -  yellowed or dead
Roots  -  internal feeding
Whole plant  -  internal feeding
Whole plant  -  plant dead; dieback
Symptoms
The larvae feed on the roots of young and mature plants.

In carrots the young plants are attacked on the tap roots and may die, leaving gaps in the crop. Larger carrot plants are attacked on the base of the tap root and lower down, showing irregular brown channels under the surface, from which the creamy-white larva (maggot) can be extracted. Where damage to plants is severe, the leaves become reddish in colour and the plant may die, particularly in dry conditions.

In parsnips the damage is similar to that on carrots, but usually it is confined to the top 15 cm of the root.

In celery the larvae bore into the roots, crown and petioles, resulting in yellowing of the leaves and reduction in growth or death of young plants.

In parsley the larvae live in the surface of the tap root and in the lateral roots.
Prevention and control
Introduction

P. rosae causes economic damage over most of its range and some form of control is needed. Chemical control is probably still the most commonly used method. There are methods of forecasting the possible size of outbreaks using the accumulated day-degrees method.

Cultural Control

Where crops of carrots, parsnips, celery or parsley are grown in short rotation close to earlier crops, population levels of the pest may become high. New plantings should be grown away from earlier crops. In Europe film covers over seedings have reduced the infestation by larvae.

In Sweden Ramert (1996) showed that intercropping with Medicago littoralis reduced the level of infestation with carrot fly but reduced the crop yield; onion has a similar effect.

Badly infested crops should be disposed of so that the larvae cannot complete their development. Adult flies require shelter and reduction of tall vegetation around fields will minimise the risk of infestation.

There are local methods of varying the time of planting of the crop to avoid coinciding with the emergence of the adult fly. These methods of control vary with different localities and the most similar climatic area should be used as the model.

Host-Plant Resistance

Ellis et al. (1993) showed that the Libyan Daucus capillifolius had greater resistance to P. rosae than commercial carrot varieties and that crosses showed some increase in resistance. There is also variation in the natural resistance of carrot varieties. Cole (1985) showed that the resistance of different carrot varieties was related to the increased concentration of chlorogenic acid in the peel of more resistant varieties.

Biological Control

Attempts to use parasites to control carrot fly have not been highly successful. Maybee (1954) considered the introduction of Chorebus gracilis and Basalys tritoma into Canada but they failed to become established.

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Impact
On carrot P. rosae can be a severe pest, killing many seedlings early in the year or making the final crop unsaleable due to the level of larval mines, secondary rots and the uneven size of the roots. The first generation of larvae feed on the apices of the tap roots and may cause reddening of the foliage. It is the second generation which causes the most important damage to carrots. The surface mines render the carrots unsaleable, causing a reduction in quality rather than quantity.

Coppock et al. (1975) recorded that in England 60% of untreated carrots may be damaged if not harvested by early January. Toms (1972) estimated that an average attack resulted in 30% of carrots being rendered unsaleable.

On celery the second generation of the fly can also cause major losses by damaging the outer stalks and the base, and in some areas all crops are protected against infestation.
Related treatment support
 
External factsheets
BBC Pest and Disease Factsheets, British Broadcasting Corporation (BBC), English language
Plant Health Australia Factsheets, Plant Health Australia, English language
Pennsylvania State University Insect Pest Fact Sheets, The Pennsylvania State University, English language
PlantVillage disease guide, PlantVillage, English language
Pennsylvania State University Insect Pest Fact Sheets, The Pennsylvania State University, 2010, English language
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