Disease of the Month - Post-Harvest Physical Injury

 
  Hort Snacks - September 2018
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 Crops Affected: various fruits and vegetables

Symptoms:

  • Post-harvest physical injury can occur on most fruit and vegetables during any of the many handling processes or during storage. Injuries may include:
    • Impact splits – fruits, roots and tubers from the impact when they are dropped
    • Internal bruising – not visible externally, caused by impact
    • Superficial – surface grazes, skinning or scratches to the skins and outer layer of cells
    • Crushing/compression – leafy vegetables and other soft produce; may also occur in firmer produce in some situations
    • Shatter cracking - result of physical injury, due to rough handling
      • High turgor (full of water) carrots tend to be more prone to damage
    • Cuts – penetrating slices or cuts which damage deeper tissues
    • Breakage – portions of the produce may be broken off completely (e.g. roots, leaves, etc.)
    • Wilting – loss of turgor in leaves, roots, etc., may manifest as shrivelling, rubberiness, colour loss, etc.
Causes:
  • Blackspot Bruising – Individual cells are ruptured below the skin without breaking the skin. Bruises develop within a couple of days and are only visible when potatoes are peeled.
  • Shatter Bruising – Typically due to rough or improper handling. Thin cracks or splits occur in the flesh of the tuber, particularly in larger tubers. Thumbnail cracks, which occur when cold tubers are handled in storage, are a form of shatter bruising.
  • Crushing/Compression – Depending on the crop and the severity, can range from pressure bruises to cracking. Occurs as a result of excessive weights or bulk pile depths. Softer produce is more susceptible to crushing.
  • Splits/Cuts – Improper belt speeds, insufficient padding or belt/roller loading, sharp edges or corners, damaged pallets or handling equipment with pointy, sharp or rough protrusions
Harvest Conditions and Post-harvest Injury:
  • Crop maturity, harvest temperatures and moisture conditions have a significant influence on harvested produce quality. Ideally, all produce should be fully (or appropriately) mature when harvested. For potatoes, tops should have naturally died down or have been killed prior to harvest. Top killing encourages skin set.
Harvest Conditions:
  • Potatoes should ideally be harvested at temperatures between 7C and 15C and with good, average soil moisture.
    • When potatoes are harvested at warmer temperatures (greater than 18-20C) and under drought stress, expect more blackspot bruising and potentially more storage diseases, such as leak and pink rot.
    • When potatoes are harvested at temperatures less than 7C and with increasing soil moisture and tuber water content, you can expect to see a greater incidence of shatter bruising. This is true with other root vegetables.
    • Repeated exposure of tubers to temperatures less than 5C can lead to sugar to starch conversion and darker fry colour.
    • Frozen tubers will occur when temperatures go below 0C. It is almost impossible to store a crop of potatoes with more than 5 percent frozen tubers.
    • Other vegetables will also be affected by freezing – in some cases, allowing them to thaw prior to harvest will be acceptable
Management:
  • Avoid harvesting carrots (and other root vegetables) at cooler soil temperatures (e.g. avoid early mornings) or when they are fully turgid
  • Store bulk vegetables according to established pile guidelines (depth, aeration, temperature)
  • Store produce in appropriate sizes/volumes to prevent compression or bruising injury
  • Rough handling of produce during harvest, grading and in the post-harvest and storage stages can result in increased incidence of storage diseases, reduce quality and crop value.
    • Ensure all equipment is properly calibrated prior to use. Avoid drops of greater than 12 inches and avoid over-piling. Ensure that handling equipment is properly operated, to minimize damage
  • Proper post-harvest curing for wound healing is also an important step
 
 
 
 
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on August 30, 2018.