Symptoms
Symptoms start on younger leaves. Leaf veins first remain green, but black spots develop along the line of the veins. Leaves near shoot tip small and chlorotic/necrotic.
Reasons
Severe manganese deficiency.
Could be confused with late blight (Phytophthera infestans) but manganese deficiency has no smell and necrosis of stem base.
Manganese deficiency is normally limited to high pH soils, where manganese in the soil is unavailable for the plants. Manganese deficiency occurs on medium to low pH soils, if the soil preparation has created a loose soil with high oxygen content.