Potassium deficiency (K)
Bronzing of leaves and necrosis of leaf margins and tips. Stunted bushy plants with small leaves and very premature senescence before adequate tuber bulking. Increased black spot in tubers also indicates K deficiency.
Treatment: Emphasis should be on providing adequate reserves of soil K by applying Patentkali®, KALISOP® or Korn-Kali® prior to planting. Additionally, in case of deficiency a foliar application of Potassium sulphate (HORTISUL®) can effectively boost K and is particularly useful for crops in very light soils.