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Ministry of Agriculture, Food and Rural Affairs


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


  • Mid-shoot leaves lighten in colour, then turn purple and eventually necrotic spots appear along the margins of young blades
  • Leaf margins dry up and roll up or down, and blades become distorted and ruffled
  • Later in the season, interveinal areas of older leaves at the base of shoots turn violet brown to dark brown, especially near the clusters.  This is called “black leaf”
  • Severe potassium deficiency greatly reduces vine vigour, berry size, and crop yield

Often Confused With
Ozone injury – occurs after thermal inversions during the summer; only exposed basal leaves affected

European red mite – adults, nymphs and eggs visible

Late spring frost – more severe in low spots

Natural senescence of basal leaves in late summer or early fall

Scouting Notes
Symptoms become visible in mid- to late summer on mid-shoot then basal leaves.  Black leaf is especially pronounced on heavily cropped vines because after veraison, maturing berries become a potassium sink.

Management Notes
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.  Foliar sprays may be used but deficiency should be confirmed with tissue analyses before use.

Potassium deficiency in grapevines

Potassium deficiency in grapevines

Potassium deficiency in grapevines

Potassium deficiency in grapevinesClick to enlarge.