Often termed “Hidden Hunger” as plants fail to thrive, potassium stress is typically seen on the leaf tips and margins of older leaves, which turn from green to yellow, eventually becoming brown and necrotic. Plants tend to be slower growing, lax and more prone to heat/water stress.
Potassium deficiency tends to affect plant development and yield building from flowering onwards, leading to poor fruit set with low dry matter and sugar production. Potassium is required in the largest amount of any nutrient and soil supply often fails to meet plant demand, especially during periods of heat stress. Potassium stress is often worse in alkaline soils or following applications of magnesium-based lime or fertiliser.
Check soil status and correct if necessary. Time fertilisers to match plant demand. Foliar treatments from flowering onwards, or in response to symptoms can be very effective in maintaining plant growth and health.