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Saturday, August 27, 2016

Late-season fungicide sprays in grapes and potential effects on fermentation

My husband shared this article with me from Michigan State University called Late-season fungicide sprays in grapes and potential effects on fermentation. I thought about one of the questions that I had to answer when I took the U.C. Davis Enology and Viticulture Certification course. The question consisted of a very long scenario which included the fact that the original fruit was in excellent condition and then "Why was there the odor of sulfides emanating from a tank of fermenting Chenin blanc." I answered the question as best as I could but totally missed the mark. The key is "original fruit was in excellent condition". At that time, I couldn't connect the fact that fruit in excellent condition may be the result of a well executed spray schedule that included sulfur as a fungicide.
The above article is all about late season use of fungicide sprays and the pre-harvest interval or PHI timing of sprays and its effects on fermentation.
Here is my summary:
Fungicide Pre-Harvest Interval (PHI) Effect on Fermentation
Oxidate Day of harvest No issues
Biofungicide
Serenade
Day of harvest No issues
Sulfur 5-6 weeks H2S (hydrogen sulfide) or rotten egg smell
Copper Late season usage Copper is toxic to yeast and even non-lethal doses of copper can cause stress on the yeast, potentially leading to incomplete fermentation and release of undesirable metabolites, all leading to wine aroma defects
Captan Late season usage Can delay the start of alcoholic fermentation, captan-treated grapes retained a definite cloudiness after six months of storage
Manzate 66 days before harvest Preventing chemical residue and degradation product left on fruit; not necessarily affecting fermentation
Ridomil MZ 66 days before harvest Preventing chemical residue and degradation product left on fruit; not necessarily affecting fermentation
potassium bicarbonate
(Kaligreen, Armicarb, Milstop)
Late season usage Contains potassium so best to avoid a heavy application shortly before harvest
Botryticides Elevate, Vangard and Scala Late season usage Safe for both alcoholic and malolactic fermentation
strobilurins
(i.e., Sovran, Abound)
Late season usage No effect on fermentation but late-season use of strobilurins is not recommended due to possible fungicide resistance issues
sterol inhibitors
(i.e., Elite, Rally)
Late season usage No effect on fermentation
powdery mildew fungicide Quintec Late season usage No effect on fermentation
JMS Stylet Oil Good late-season spray to reduce powdery mildew and European red mite Some evidence that late applications depress Brix (sugar) accumulation due to a temporary reduction in photosynthesis; other California studies show no effect on fermentation

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