Carrots – Forking, Cracking, Staining

Crops Affected: carrots and other root vegetables (e.g. parsnips, radishes, beets, etc.)

Causes:

• Anything that can cause the main tap root to die back can result in forking
• Any obstruction or compression of the soil at the root tip at a young age will cause bending, forking, or other deformations of the root
• Forking may be caused by a range of different things, including:
  • Attack by insects, diseases, or nematodes
  • Mechanical damage from deep and/or too close cultivation
  • Physical obstructions (e.g. stones, chunks of organic matter or debris)
  • Damage by chemicals or fertilizers
  • Poor soil conditions, including:
    • Natural or manmade compaction layers
    • Heavy clays
    • Poor soil drainage or waterlogging which results in poor aeration
    • Excessive drying of the soil during early tap root development can cause heavier soils to compact
  • Excessively close plant density can cause forking or twisting
• Growth cracks generally occur due to fluctuating soil moisture during the season
  • Very dry conditions will slow root growth
    • If this is followed by adequate to heavy moisture, it will cause the root to grow rapidly, causing splits
  • Wide spacing and/or larger carrots tend towards splitting
• Splitting is like growth cracks however they may occur throughout the season (growth cracks) or because of physical injury during harvest or post-harvest processes (shatter cracking)
  • Harvesting under cold soil conditions may result in more cracking, splitting, and breaking
  • High turgor (full of water) carrots tend to be more prone to damage
• Staining may result if carrots are not washed shortly after harvest, prior to storage
  • Delays in washing may increase staining
  • Some diseases will cause discolouration or staining, but because of colonization and tissue damage, not just a physiological change

Symptoms:

• Forking can look like anything from a misshapen root tip, or a slight shortening of the root, through to the development of a multi-rooted carrot with several divergent tap roots
• Cracking and splitting appear as vertical cracks running along the length of the tap root
  • Cracks may be thin or wide, depending on the age of the carrot at the time of splitting
  • Early growth cracks will have a layer of wound tissue (suberized tissue) covering damaged tissues, resulting in a rougher appearance
  • In some cases, secondary pathogens (bacteria/fungi) will colonize splits or cracks
• Stains result from prolonged contact between soil and roots

Management:

• Ensure adequate water is applied
  • Avoid overwatering
• To avoid forking
  • Ensure soils are well drained, free from debris or stones
  • Ensure that soils are loose and friable, without hardpan or compacted layers
  • Protect plants from attack from pests at all growth stages
  • Avoid mechanically damaging growing plants with cultivation
• To minimize cracking and splitting
  • Excessive nitrogen application can cause plants to grow too quickly and crack, particularly if rains come shortly after application
  • Avoid harvesting carrots at cooler soil temperatures (e.g. avoid early mornings) or when they are fully turgid
• To prevent staining
  • Wash carrots after harvest, prior to storage
• Grow conical-shaped carrots
  • They tend to be more tolerant of forking/cracking/splitting conditions