Potassium deficiency

Yellowing and brown necrosis spreading from margins between veins of older leaves (J. O'Sullivan).

- older leaves turn yellow and then necrotic in interveinal and marginal zones.

- symptoms usually develop some time after establishment, during the storage root development phase.

- young leaves remain of normal size and colour (but purple tips may be less purple than normal).

- mature leaves may show a pale green interveinal mottle.

- storage roots are small and thin.

This is a very common cause of low yields. Root crops have a high requirement for potassium, and several successive crops may deplete the soil of potassium.

Common when the soil has a history of cropping with root crops without potassium fertiliser.