Pests and diseases management of Carrots

•  Leaf blight (Alternaria dauci)

The disease is caused by the fungus . Dark-grey to brown, angular spots form on leaves. Surrounding tissue yellows and affected leaves eventually die. Older leaves are attacked first and only in very severe cases are younger leaves affected. Large spots can girdle leaf petioles and kill leaves without spots developing on individual leaflets.

During warm moist weather, dying of affected leaves may occur so rapidly that plants appear scorched. This fungus can also cause seedling damping-off. The fungus is seed-borne and survives in the soil crop debris.

Photo. Leaf blight symptoms on carrot

 

Management:

• Use resistant hybrids where available.
• Use certified disease-free seeds. In case of using own seeds, hot water treat seeds.
•  Practice crop rotation and good field hygiene.
• Enhance aeration of crop field by less dense crops and ridge cultivation.
• No or little N-fertilization.
• Monitor fields regularly to be able to react properly.
• Copper treatments can reduce infection. 

• Powdery mildew

The disease is caused by the fungus called Erysiphe polygoni (E. heraclei). It is characterised by the development of white, powdery fungal growth on leaves. Affected leaves become chlorotic and eventually die. The fungus is seed-borne.

 

Photo. Symptoms of powdery mildew on carrot

Management:

• Use certified disease-free seeds If using own seeds hot water treat the seeds.
• Practice good field hygiene
• Spray with sulphur based products where acceptable

Storage Diseases

Major post-harvest losses in carrots are due to Sclerotinia rot. The Sclerotinia fungus infects the carrot roots in the field through the crown. During storage, the Sclerotinia fungus produces a white, cottony mycelium which covers the roots. Infected roots are usually soft and watery.

Storage losses to Sclerotinia can be minimized by:

(1) pre-harvest application of a registered fungicide such as Bravo 500

(2) rapid removal of field heat from freshly harvested roots

(3) increasing row width to increase ventilation since prolonged periods of leaf wetness induce rot

(4) crop rotation

(5) post-harvest application of a registered antimicrobial such as Dowicide (O- phenylphenol) at a concentration of 98 g/L.