Many bacterial, fungal, and nematode diseases can affect carrots during cultivation and storage.
There are several carrot diseases and control is necessary to get a better yield.
Diseases that affect this vegetable can result in reduced yield, difficult harvesting if the tips are limp, and reduced market value.
Carrots are susceptible to many diseases. As carrots grow underground, infections can spread and may not come to light until the harvest. However, disease symptoms can be seen above the ground if you carefully watch carrots growing.
An accurate diagnosis of the disease will help prevent its spread and help prevent the transfer of disease from field to field.
Here, we will look at some common diseases of carrots and their control.
Common Carrot Diseases and their Control
Several bacteria and fungus can cause diseases in carrots; below are some common carrot diseases and control methods to prevent them.
Cercospora Leaf Blight
A fungus called Cercospora Kikuchii causes Cercospora leaf blight. The fungus remains in the infected debris or seeds during winter.
Any tissue of the carrot above the ground can be affected by Cercospora disease. However, the disease’s symptoms are generally more severe and prominent on the edges of the leaves.
A brown spot with a dark brown border appears as an initial appearance on the infection site. The leaflets turn yellow and curl around the edges as the disease progresses. A toxic chemical produced by the pathogen usually develops around these spots.
Damage to petioles, stems, and flower parts is usually long and dark brown. Severe leaf loss can occur under severe infection. Symptoms of the diseases include:
- Infection may appear along the edges of the leaves, but the spots spread, causing curling of the leaves.
- The infection spots that are not on edge are circluler.
- The spots are initially small chlorotic spots that enlarge and become tan, brown, or black, with a necrotic center surrounded by a yellowish rim.
- These disease spots can easily be mistaken for Alternaria Blight, which is usually more irregular and darker in color than Cercospora leaf Blight.
Controlling Cercospora Leaf Blight
Before planting, make sure seeds are disease free or treat them with a fungicide. Remove diseased crop residues by ploughing into the soil to encourage decomposition and rotate crops every 2 to 3 years.
Effective control of this disease requires an integrated approach to pest control. Integrating and implementing proactive methods such as sowing disease-free seeds, using resistant or more tolerant carrot varieties, crop rotation, and reducing crop stress via appropriate nutrition and irrigation.
Seasonal management decisions are then made based on regular examination of fields to monitor disease progression, weather forecasting, and using thresholds to assess whether pathogen populations have reached levels that will cause crop damage.
Black Root Rot in Carrots
Thielaviopsis basicola is a plant-pathogen fungus that causes black root rot in carrots. Black root rot is mainly a post-harvest disease. This pathogen is found worldwide and has many hosts – legumes, potatoes, squash, and several ornamental and woody plants.
This disease is seen from time to time in seedlings or mature carrots in the field and is more consequential in soils that contain high organic matter.
This disease causes random irregular black lesions. The discoloration is limited to the epidermis, and the black coloration is a dark brown to the black mass of chlamydospores. This disease rapidly attacks injured tissues, supported by long post-harvest without refrigeration.
Acute root infections can lead to wilting, stunting, and productivity loss, but unmarketable carrots cause most losses. The disease symptoms include:
- The roots of the plant appear as brown sores in the early stages; after that, they enlarge and turn black.
- Disease-affected large areas or all roots; the pathogen often destroyed small roots.
- Occurrence of this disease can happen at any stage of plant growth; it can be with seedlings to plants ready for sale. Infected plants can be seriously stunted in growth.
Also Read: 5 COMMON DISEASES OF CEREAL CROPS
Control for Black Root Rot
Environmental conditions are essential to manage and prevent root rot disease in carrots. Keeping the soil pH at 5.5 will lower initial infection.
Since the disease occurs mainly after harvest and mechanical sorting, prevention of injury and prompt removal of field heat are necessary controlling measures. Under favorable storage conditions, this disease is rarely a severe problem (0-1˚C).
The disease can be effectively controlled by soaking harvested carrots in cooled chlorinated water or a potassium solution sorbate and propionic acid.
Treatment with fungicide against black root rot provides protection. Removing infected plants and plants near them is an excellent natural way to control this disease.
Bacterial Soft Root of Carrots
Many bacteria cause soft rots in carrots; Pectobacterium carotovorum, Dickeya dadantii, and certain species of Pseudomonas, Bacillus, and Clostridium are the most common. Soft rot appears as a smooth, watery decay of the main root.
The disease quickly eats away at the core, generally leaving the epidermis intact. A funky smell may be linked with soft rot disease. Upper-ground symptoms include yellowing, wilting, and general defoliation.
Field soft rot is generally linked with high temperatures and poor drainage, lowlands, or leaking irrigation pipes. The most susceptible time for carrots to be infected is when the roots are mature, and the temperature is warm.
Symptoms of the disease include:
- Soft, wet, decaying brown or cream-colored soft tissue.
- The disease progresses inwards by starting on the surface of the carrot
- A dark brown or black border separates the infected and healthy tissue.
- Shallow necrotic spots on tubers caused by lentil infection.
Control for Soft Root Rot
Ensure good drainage in the cultivation field, and protect the crop from injuries and damage. Do not continue watering mature carrots during the year’s warm months.
Transport the carrots to the packing area, taking care not to crush them, and store them in the refrigerator. Adding chlorine to wash for washing carrots helps remove soft rot bacteria from the surface of carrots.
Cavity Spot
The pythium fungus causes cavity spot disease in carrots; a calcium deficiency can lead to cavity spots.
Cavity spots are characterized by sunken, elliptical to irregularly shaped lesions extending along mature carrots’ main root. The diameter of these individual cavities is usually less than 1.3 cm; however, they can be bigger, particularly in cultivated varieties.
Infection occurs anywhere along the main root, but lesions are higher in the upper third of the root and are usually found where lateral roots emerge from the main root. The lesions begin as sunken punctate spots and typically enlarge as the roots mature.
Studies show that cavity spots are more common in late summer and autumn crops, in soils with a ph below 7, and acute in following crops.
Control for Cavity Spot
Integrated management programs such as tolerant cultivars, rotation, calcification, scheduled harvesting, and metalaxyl application can help lower cavity spots’ occurrence.
It is also beneficial to grow carrots where this disease is least likely to occur and avoid areas for summer and fall crop cultivation where previous crops were affected by cavity spot. Cultivating cavity spot disease-resistant varieties such as Stefano, Navarre, Crusader, and Nandor is helpful against this disease.
Monitor the disease’s development throughout the crop’s life in areas with a history of this disease. Monitor the level of infection by taking samples one month before the expected harvest date; this will help you decide when to harvest.
Harvest carrots when they reach marketable size, as over-matured carrots will have more cavity spot.
Sclerotinia Rot
A fungus, Sclerotinia sclerotiorum causes sclerotinia rot in carrots, sclerotinia rot, is also called watery soft rot or cottony rot. Above and underground parts of the carrot is affected by this disease.
This disease is a serious threat in many vegetable-growing regions. The disease can affect carrots in storage in the field.
White fungal growths and small black granules appear on the carrots. The roots are covered with white cotton growths.
This disease is significantly harmful to carrots in storage. During long-term storage during the winter months, significant losses can occur. Losses can go up to 50% under the optimal conditions for pathogens. Symptoms of sclerotinia rot include:
- In the field crop, water-soaked lesions at the base of the leaves.
- Under highly humid conditions, the infection can be accompanied by the growth of white cottony mycelium on carrots and harvest residues.
- The pathogenic white mycelium in storage grows quickly and infects large areas of carrots.
Conclusion
Various diseases can reduce carrot yield and quality. There are many carrot diseases and control of these diseases is necessary as they can cause loss to farmers and the economy.
Roots destined for the fresh market should be almost flawless; however, at least three bacteria and twelve fungi cause attenuated lesions.
The presence of severe infections leads to unproductive crops and yield losses. Various pathogens are after the carrot crop, some damage them in the field, and some are dangerous while storing them.
In addition to chemical disease control, many pest control methods are used to limit economic losses from disease, including cultural practices such as irrigation management, crop rotation, clean seed production, and soil preparation.
