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Ministry of Agriculture, Food and Rural Affairs

Potassium

Potassium (K) is important for fruit colour, winter hardiness, tree growth and disease resistance. 

Identification

  • More a problem in plums than other stone fruits
  • Terminal shoots and terminal portions of main scaffolds of trees may die when crop load is heavy
  • Usually first appears on midshoot leaves
  • Pale, interveinal purpling at leaf margin, later expanding into the centre
  • Leaf margins become brown and curl or roll upward, especially in peaches
  • Necrotic spots develop along the margins and between leaf veins, eventually cracking or tearing as the tissue dries
  • Marginal scorch is particularly evident in plums
  • Fruit will ripen unevenly and have poor/variable colour development
  • Fruit colour is poor, either lacking colour or having a dull dirty looking orange colour
  • Leaf margins become brown and curl or roll upward, especially in peaches
  • Deficiency can increase susceptibility to fireblight

Often Confused With 
Leaf scorch – damage to succulent spring growth following high winds at high temperatures

Scouting Notes
Symptoms are usually present on the upper part of the tree first, most pronounced on midshoot leaves.
 
Management Notes

Potassium deficiency predisposes prunes and European plums to perennial canker.

Potassium deficiency symptoms occur when uptake from the soil is compromised due to waterlogging or extremely dry soil conditions or soil compaction.  It can be easily leached from sandy soils.  High levels of calcium, magnesium, sodium, nitrogen or phosphorus can affect uptake, especially if potassium deficient in the soil.  Deficiency should be confirmed with tissue analyses. For application rates of potassium, see nutrient sufficiency ranges for tender fruit. 

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