Low Magnesium status affects older leaves first. The main veins on the leaf remain dark green, while the interveinal leaf area goes uniform pale green to yellow, eventually becoming brown and necrotic. Magnesium deficiency results in poor nutrient recovery, low growth rates, increased biotic stress and early senescence.
Magnesium stress can affect plant uptake of nitrogen and potassium, leading to early maturity and poor development of fruit, with low sugar content. In addition, plant defence and disease resistance can be restricted. Magnesium stress is often worse in compacted or alkaline soils, during hot, dry growing conditions and when crops are fed high levels of nitrogen-potassium fertiliser.
Check soil status and correct if necessary. Foliar treatment as soon as symptoms appear can be very effective. Routine applications of foliar magnesium can improve the later stages of yield building and quality forming.