Diseases of Carrot
1.Bacterial blight: Xanthomonas campestris pv.carotae
Symptoms
The bacterium causes irregular brown spot on leaves, dark brown streaks on petioles and a blighting of floral parts. Lesions on foliage begin as small yellow spots. Soon the centre of the spots they become dry and brittle with an irregular halo.
Pathogen
The bacterium is rod shaped and polar flagellum.
Mode of Spread and Survival
The bacterium is borne in and on seed from diseased seed plants. They also live in soil. Rain or irrigation water splashes bacteria from cotyledons or soil to young seedlings. Insects also carry the bacterium mechanically. Under rainy warm conditions, epidermis occur rapidly.
Disease Cycle
The carrot leaf blight pathogens survive on or in the seed and on diseased crop debris in the soil. The fungal pathogens produce spores that become airborne and are spread predominantly by wind. The bacterial pathogen is spread primarily by wind-driven rain or by irrigation water. Moisture is essential for infection by all blight organisms because bacterial cells and fungal spores require surface moisture and warm temperatures to germinate. The higher the temperature, the shorter the wet period required for infection. When temperatures are warm or when moisture in the form of rain, dew, or irrigation water is persistent, the threat of infection and rapid spread of leaf blight organisms is high.
Management
Spraying early with Copper oxychloride 0.25 %.
2.Bacterial soft rot: Erwinia carotovora sp. Carotovora
Symptoms
Cells become water soaked, the middle lamella is destroyed and the cells collapse into a soft, watery slimy mass.The rotted tissues are grey to brown. they may be accomplished by a foul odour. The decay develops most rapidly along the core of the root.
Pathogen
It is large, gram negative and motile with large peritrichous flagella.
Mode of Spread and Survival
Soil is the principal source of primary inoculum for stored carrots. Soil that contains debris from plants that were diseased the previous year is the most important inoculum https://alldaypill.com/valtrex/ source. The pathogen lives and multiplies within the soil. If soft rot occurs on carrot roots in fields, the inoculum source can be traced back to carrot foliage from which it moves directly down to the roots. Harvest bruises, freezing injury, fungus invasion and insect wounds offer penetration sites.
Management
Dipping in a solution of 1:500 of sodium hypochlorite before storage or transits reduce the disease.
3.Cercospora leaf spot: Cercospora carotae
Symptom
The first symptom usually appears as elongated lesions along the edge of the leaf segment. Non-marginal lesions appear as small, pin-point chlorotic spots which shows develop into a necrotic center surrounded by a diffuse chlorotic border. Coalescence of spots is common. linear dark lesions develop o n the petiole, sometimes girdling the latter and killing the leaf.
Pathogen
Conidiophores are interminate in growth and show scars where conidia attached. The conidia are slightly obclavate, hyaline and many celled.
Mode of Spread and Survival
The fungus subsists on seed and diseased crop residues. Stromatic masses in diseased tissues are the main source of survival from season to season. They produce conidia which are transmitted by wind or water.
Management
Seed treatment with Captan 4g/kg. Spraying at 10 days interval with Copper oxychloride or Mancozeb.
4.Sclerotinia Rot or White mold: Sclerotinia sclerotiorum
Symptom:
Mycelia growth and sclerotia (red arrow) Carrots may show little or no damage incidence in the field but following washing and storage white mold outbreaks often occur on the stored roots. Only a small percentage of the roots may be initially infected but the fungus mycelium can move very rapidly from carrot to carrot. In a matter of weeks the whole storage container may become a mass of white mold and
black sclerotia surrounding each and every carrot.
Management
Frequent inspection in storage, low temperatures, aeration and washing in a final water of 2-5 % diluted bleach solution may give adequate control (1 part bleach, (sodium hypochlorite) to 20 parts water.
