Carrot Diseases

1
Carrot Diseases

• Alternaria Leaf Blight - Alternaria dauci
• Cercospora Leaf Blight - Cercospora carotae
• Pythium Root Dieback - Pythium spp.
• Crater Rot - Rhizoctonia carotae
• White Mold (Cottony Soft Rot) - Sclerotinia
  sclerotiorum

• Root Knot - Meloidogyne spp.

• Aster Yellows

2
Alternaria Leaf Blight
3
Alternaria Leaf Blight
4
Cercospora Leaf Blight
5
Cercospora Leaf Blight
6
Carrot Diseases - Alternaria and Cercospora Leaf
Blight - Key Points

• Pathogens
• Alternaria dauci
• Distribution
• both common in the temperate zone
• Cercospora more readily attacks young leaves
• Alternaria more readily attacks mature tissue
• Symptoms
• leaf symptoms similar but Alternaria leaf spots
  more irregular, darker brown than Cercospora
• with both, lesions can girdle petiole, cause
  death of entire leaf
• Transmission
• both pathogens can be disseminated in or on the
  seed
• spores of both disseminated by wind and splashing
  rain
• both overwinter in infected debris in soil, weed
  hosts

• Cercospora carotae

7
Carrot Diseases - Alternaria and Cercospora Leaf
Blight - Control Strategies

• Use seed produced in arid regions of the country
• Fall plowing with a 2-3 year rotation
• Use currently registered fungicides
• Resistant varieties (both Alternaria and
  Cercospora)
• Caropak
• Choctaw
• Danvers 126

• Huron
• Orlando Gold
• Seminole

8
Pythium
9
Pythium
10
Pythium
11
Carrot Diseases - Pythium Root Dieback Key Points

• Symptoms
• wilting or stunting of top growth (due to
  vascular disruption of roots)
• forking of roots due to root tip dieback,
  unacceptable for processing
• More serious in high organic soils (muck)
• Various species of Pythium are implicated in this
  disease

12
Carrot Diseases - Pythium Root Dieback Control
Strategies

• Rotation - at least three years without carrots
• Avoid wet soils early in season

13
Crater Rot
14
Carrot Diseases - Crater RotKey Points

• Pathogen Rhizoctonia carotae
• Losses can reach serious proportions in cold
  storage under high relative humidity
• Initial symptoms are small white hyphal knots
• Small pits follow, which then enlarge into sunken
  craters

15
Carrot Diseases - Crater Rot Control Strategies

• Any practice that hastens the drying of the top
  soil, such as cultivation, weed control and wide
  rows, should be practiced
• Prompt lowering of the storage temperature to
  near 32 F is important
• Store roots at relative humidity below 95
• Do not reuse crates unless they have been steamed
  or dipped in an acceptable chemical disinfestant

16
White Mold
17
Carrot Diseases - White Mold Key Points

• Pathogen Sclerotinia sclerotiorum
• Fungus with very wide host range
• Disease also called "Cottony Soft Rot"
• Overwinters in the soil as sclerotia
• Field infection is the most common, but infection
  in storage can occur due to contaminated crates
  or other storage containers/structures
• Sclerotinia is a cool temperature pathogen,
  infecting primarily at temperatures of 55-65 F

18
Carrot Diseases - White Mold Control Strategies

• Three year rotations using cereals and forage
  grasses
• Storage crates and facilities should be
  disinfested
• Storage temperature should be near 32 degrees F
  with a relative humidity of 95 or below

19
Root Knot Nematode
20
Root Knot Nematode
21
Carrot Diseases - Root-Knot Nematode Key Points

• Pathogen Meloidogyne spp.
• This nematode is present in all parts of the
  world and can infect every vegetable
• The pathogen stimulates the root tissue causing
  giant cells to form which account for the galls
  seen on the roots
• Attacks by the nematode just behind the growing
  tip of the root cause excessive branching of the
  roots
• Infection seldom kills the host plant, but
  wilting, poor root quality and poor yields may
  result

22
Carrot Diseases - Root-Knot Nematode Control
Strategies

• Fallow cultivation may help
• Rotate with corn, grasses and small grains
• Chemical fumigation, if permitted (not practical
  for the home gardener)
• Rotation with other resistant varieties of
  vegetables such as Beefmaster, Better Bush,
  Empire, Celebrity, etc. tomatoes
• See UWEX Publication A3110 for other resistant
  tomato varieties

23
Aster Yellows
24
Aster Yellows
25
Aster Yellows
26
Aster Yellows
27
Carrot Diseases - Aster YellowsKey Points

• Pathogen Aster yellows phytoplasma
• Wide host range - at least 300 species in 48
  families. Vegetable hosts include carrot,
  lettuce, escarole, endive and celery
• Leafhopper transmitted
• Symptoms
• yellowing and bronzing of foliage
• brooming of leaf tissue emerging from crown of
  plant
• hairy roots and internal root necrosis
• Overwintering
• perennial weeds and ornamentals
• insect vector on grasses or grain crops
• leafhopper vectors from southern US carried north
  by wind

28
Carrot Diseases - Aster Yellows Control
Strategies

• Eradicate overwintering weed and ornamental
  plants
• Do not plant adjacent to other plants which are
  diseased
• Plant as far as possible from grain and grass
  crops
• Regular insecticide program to reduce leafhopper
  population
• No resistant or immune varieties as yet