WTN: question re sulfur

Paul, this is most instructive, thank you.

When dusting vines with sulfur, is it the actual sulfur (elementary sulfur) that slows down or kills the bacteria, mold, or fungus responsible for powdery mildew? I always thought because of the heat of the sun and the presence of oxygen in the air that SO2 is produced and this actually slows down or kills the powdery mildew. Brian mentioned that it is not recommended to dust the vines on days above 85 deg- Why is this? Placing a sulfur strip into a basket attached to a chain (without burning it) and just lowering it through the bung hole of a barrel (empty of course) surely wouldn’t sanitize the barrel. Heck, I don’t think it does anything.

Salute

Throwing my two cents' worth in here, a lot depends on where you're growing grapes. When it comes to "powdery" mildew (don't know the scientific name), sulfur apparently works strictly as a preventative measure but I don't know the mechanism. Once powdery mildew is established, the preferred chemical is lime sulfur (whatever that is). Copper sulfate is, as Paul wrote, combined with sulfur in "Bordeaux mixture" and is used to kill both powdery and "downy" mildew. Downy mildew is not a factor west of the Rockies and so sulfur is used alone in the West. So unlike east of the Rockies and in Europe, copper sulfate is seldom used during the growing season in California, although it can be used as part of a dormant spray to kill overwintering fungi. On the heat thing, it's my understanding that applying in high temperatures can actually burn the foliage. The good news is that the same temperatures that cause that problem also are not friendly to powdery mildew so that when daytime temperatures reach 90 or so, applying sulfur is no longer necessary.

It does seem backwards to allow sulfur and copper in organic grape growing, but not to allow SO2 in winemaking. I believe it is less a matter of "organic" and more a matter of political correctness. The collective consumer still believes that sulfites were never added to wine until the 1980s, when the words "Contains Sulfites" first appeared on the label, and the collective consumer still believes that it was some sort of evil happening that prompted the additions of sulfites. That same collective consumer is so in the dark about farming that you could call just about any practice "organic" and it would sell.

Michael Pollan has an interesting overview of the co-opting of the term "organic" from its introduction by Rodale back in the '30s in his book "The Omnivore's Dilemma." In food and wine, the term basically means "no chemical fertilizers or pesticides used" and ignores a host of other possible interventionist methods, for better or worse. The fact that copper and sulfur are somehow exempted from that definition is perplexing, to say the least.

Regarding Victor's question about the role of sulfur as a fungicide: it gets reduced by the fungi to hydrosulfide (HS-), which shuts down mitochondrial respiration (the same thing that cyanide and carbon monoxide do) and kills the fungus. Copper sulfate acts in a separate way, by disrupting membrane integrity. BTW, "Bordeaux mix" as devised by Prof. Millardet in the 19th Century was copper sulfate (bluestone) and wet lime, no elemental sulfur involved.

Mark Lipton

The fact that copper and sulfur are somehow exempted from that definition is perplexing, to say the least.

I'm guessing the main reason is it was really hard to do without copper and sulfur but the justification is that these chemicals are found in nature and therefore OK. In other words, a distinction is made between chemicals that are strictly synthetic and those sometimes found in nature. In that view, even if the copper sulfate is manufactured from refined copper, it meets "organic" standards. Behind such a distinction must be a belief that things "natural" are good, things manmade (and therefore not natural, man not being part of nature) are bad, forgetting (IMHO) that both natural and manmade chemicals can be either toxic or not. I should look for Pollan's book.

I think it's also interesting that even "biodynamic" viticulture, seen by many as more-organic-than-organic, allows the use of sulfur and copper. Just goes to show that there are some problems that planting by the light of the full moon and burying cows' horns at the equinox just won't solve Expedience wins over principle, apparently.