Magnesium deficiency (Mg)
Symptoms will initially show on lower, older leaves. Yellowing will first appear along leaf edges, and from there will spread to the veins. In red grapes, this yellowing will turn to red, with leaf veins and edges keeping their green colour. Lack of magnesium is one of the causes of stem dieback, resulting in withered grape-stems and, subsequently, in drying-up of grapes.
Treatment: In case of insufficient MgO-content of the soil it is advisable to apply magnesium at the time of planting, complemented by annual maintenance applications. It is recommended to use specialty fertilisers such as magnesium sulphate (ESTA® Kieserit) or potassium-magnesium fertiliser such as Patentkali®. Foliar fertilisation with Epsom salt (EPSO Top®) is highly effective if used during the crop’s periods of peak demand.