Symptoms
On the older leaves a usually irregular yellow chlorosis spreads from the outer edge towards the leaf base. Necrotic spots appear within the yellow tissue. With severe deficiency the leaf tips and margins show necroses, the so-called leaf scorch that is typical for K deficiency. Dull, pale brown patches may appear additionally, starting along the leaf veins. Old leaves fall off and trees show terminal dieback.
Salt stress may cause similar leaf symptoms.
Reasons
Potassium deficiency.
High levels of potassium are required for adequate crop growth. As significant quantities are found in the fruit and can be removed in the husk, regular applications are needed on most soils to maintain yields.
A leaf content of 0.7 % K is regarded as the threshold for deficiency.