Adhering to Best-Practices for Carrot Culture is the ounce of prevention that puts you ahead of disease pressure, but there is always the possibility that your carrot planting will be afflicted by any one of a number of carrot pathogens. Because inadvertent damage to roots, whether incurred mechanically or by pests, can often lead to secondary infections, it's also wise to scout frequently, so you can apply the pound of cure before it spreads.
While a comprehensive look at carrot pathogens is beyond the scope of this article, properly diagnosing carrot diseases before you implement a management strategy requires some familiarity with pathogens most likely to become an issue. Fortunately, cooperative extension agencies, agricultural universities, and ministries of agriculture are staffed by experts the grower can call upon for assistance in identification and management, should the need arise.
Here is a overview of the more common carrot pests and diseases.
Several leaf blights can reduce the yield and quality of a carrot crop. Common carrot leaf blights include:
Alternaria blight (Alternaria dauci)
Appearance: Brown-black lesions edged with yellow on leaf margins, beginning on the oldest leaves.
Alternaria blight often causes leaflets to curl, become dry, and eventually die. At later stages, petioles may become infected. If leaves are infected early enough, roots may never fully mature.
To help reduce risk of occurrence, as well as reduce spread of infection:
- Choose varieties with some amount of resistance.
- Reduce water on leaves by either watering in the morning or by employing drip irrigation.
- Strive for proper plant densities and do not overcrowd rows.
- Avoid applying excessive nitrogen, as this can lead to overabundant leaves and reduced air flow around the tops.
Cercospora blight (Cercospora carotae)
Appearance: First appears as small, dark spots with yellow margins, on younger leaves and stems.
See Alternaria for recommendations on how to reduce issues.
Carrot Rust Fly (Psila rosae)
Typical of many pests, the carrot rust fly is not an issue everywhere. Problems seem to be more prevalent in temperate regions. Fly larvae are problematic because they burrow into carrot roots, rendering them unmarketable.
The best methods for control include:
- Maintaining a 3–5-year crop rotation of all crops within the carrot family (Apiaceae), and locating these crops as far away as possible from the previous year's crop. (Some other crops within the family Apiaceae include parsnips, celery, parsley, dill, chervil, fennel, and cilantro.)
- Row cover is another method of exclusion. Covers should be placed over beds once the seeds germinate, and the edges should be buried in order to be effective.
Wire Worms (Elateridae, Click Beetle Family)
Wireworms are the larvae of click beetles. They can be detrimental to a carrot crop as they burrow into the roots, drilling holes that make them unmarketable.
The best methods for reducing problems with wireworms are:
- Crop rotation (rotating with non-host species).
- Avoid planting carrots in any location that was recently in sod.
- Fall plowing, to expose wireworms to predators such as birds.
Whatever and wherever you grow, following best practices and scouting are the keys to keeping your crops healthy. If you suspect that a carrot disease or pest is becoming a problem for you, establish contact with your regional cooperative extension agency or ministry of agriculture as soon as possible. The experts at these agencies can assist you with up-to-date knowledge on the proper identification of carrot root pests and pathogens, as well as the best options for management in your area so they do not become a recurrent issue for you.
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