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Ministry of Agriculture, Food and Rural Affairs

Boron

Boron plays an important role in the structure of cell walls, pollen germination/fruit set and seed development. It is also a component of protein and carbohydrate metabolism.

Identification
Deficiency

  • Poor bud burst
  • Blossoms wilt and die, while leaves usually develop normally

  • Shoot and limb dieback, may lead to development of many side branches
  • New leaves that follow shoot dieback are small, thick, misshapen and brittle
  • If severe, leaves die and limbs fail to form new buds, resulting in poor fruit set, loss of tree vigor or death

  • Small, water-soaked areas in flesh of fruit turn brown and dry out, forming spongy lesions in flesh
  • Pits are shallow, flat-bottomed with straight sides, most abundant toward calyx end
  • Skin becomes brown, rough and russeted with deep cracks extending into flesh
  • Small, misshapen fruit with irregular depressions

Toxicity:

  • Brown spotting along the midrib on the underside of leaves
  • Cankers on young twigs and petioles
  • Misshapen fruit with sunken areas on the surface
  • Yellowing of leaves and premature leaf drop
  • Shoot tip dieback
  • Gumming

Often Confused With
Pear Blossom Blast  –Blossom Blast causes blossoms to wither however, outer bark of shoots affected by blossom blast separate from underlying tissue, taking on a papery appearance

Pear Stony Pit  –Pits caused by boron deficiency are more superficial. The base of the pit is spongy in boron deficiency, not hard as in stony pit

Pear Cork Spot –Straight-sided, flat-bottomed pits with a small mass of spongy tissue set boron deficiency pitting distinctly apart from cork spot, with its large mass of corky tissue

Winter Injury –Winter injury also results in failure of buds to break dormancy, resulting in limb dieback. However, the cambium layer is white in boron deficiency and discolored in winter injury

Scouting Notes 
All symptoms are possible in an orchard depending on soil pH, texture, organic matter and moisture, but rarely are they seen on the same tree. This variation is characteristic of boron deficiency.

Boron deficiency is most often observed early in spring by fruit and leaf buds failing to break dormancy, followed by dieback of branch or blossom blasting.
 
Most likely to be found on alkaline soils or sandy knolls, boron deficiency is common in dry weather and in soils with a high pH.

Management Notes
Visual symptoms of boron deficiency are very similar to symptoms of boron toxicity.  Do not apply boron directly to the soil until a deficiency is confirmed with a soil and tissue analysis.

Boron deficiency in plums leading to cracking and splitting
Boron deficiency in plums leading to cracking and splittingBoron deficiency in plums leading to cracking and splittingClick to enlarge.