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Magnesium Sulfate Vineyard Sprays

TroubleShooting

William Foster — via e-mail asks,
Q

Is it okay to use a magnesium sulfate spray on Marechal Foch? Do the sulfate ions in solution have any damaging effects similar to using a pure sulfur spray?

A
Magnesium Sulfate (MgSO4), AKA Epsom salts, is a very common vineyard amendment. It can be applied as a foliar spray during the growing season to provide vines with magnesium and sulfur. Magnesium, especially, is critical for photosynthesis. I talked to Hans Walter-Peterson, Viticultural Extension Specialist with Cornell University about the use of magnesium sulfate sprays in the vineyard and if we should be concerned about using them during the grape-growing year. Basically, it’s fine to use during the growing year but you need to watch out as you approach harvest. As you allude to above, elemental sulfur is sometimes sprayed on vines to control powdery mildew and growers should be careful not to apply it too close to picking. Mr. Walter-Peterson tells me that MgSO4 will not break down into elemental sulfur, per se, but will break down into magnesium and sulfate ions. During fermentation, Saccharomyces cerevisiae can reduce environmental sulfate into sulfide. The yeast then incorporates some of the sulfide into amino acids, which can lead to the production of stinky volatile sulfur compounds (VSCs), with any excess converted
Response by Alison Crowe.