Symptoms of Mg deficiency develop on the older leaves first.  Chlorosis (yellowing) appears between the veins of the leaves while the veins remain green.  As a vine becomes more severely affected, interveinal chlorosis intensifies in older leaves and spreads to younger leaves toward the terminals of canes.  The younger terminal leaves may not exhibit symptoms until the entire vine is extremely deficient. Early symptoms: green leaf margins with yellow between the veins. Deficiency of magnesium appears first on basal leaves of shoots as a yellowing between veins. Symptoms progress to dead blotches on the leaves, which may be a rusty-red. Advanced stage yellow between  veins interspersed with brown or often rust-colored areas.  First chlorosis of basal leaf margins, than between and secondary veins, leaf margin burn may develop, interveinal areas become white yellow or red depending on variety.

Mix magnesium sulfate at the rate of 6 kg per 200 litres of water.  Two applications usually are adequate.  Apply the first shortly after bloom and the second two weeks later.  Each spray application requires about 400 to 500 litres of the mixture per acre to adequately cover the vines.