As the weather warms up in spring we begin to worry about mildew.Â Mildew on grapes will ruin the wine, so we have to be vigilant and make sure it does not become established on the vine.Â Mildew grows actively when the temperature is between 70 and 85 degrees for at least 6 hours during the day.Â Once spores are established, mildew infections will expand whether it rains or not.Â Grapes are susceptible to mildew until they turn color around the end of July.Â In our vineyards, we carefully monitor conditions and adjust our treatment scheduling in response.Â Our primary tool against mildew is sulfur dust, an age-old remedy that is approved for organic farming.Â Now at the beginning of May we have already made one pass through the vineyard with sulfur and will make several more.Â However, we will replace a pass with sulfur with a spray fungicide if we are also applying a foliar spray.Â In the next week we will spray withÂ zinc to assist in fruit set, so we will combine that with a fungicide.Â The added benefit is that the spray fungicide is effective much longer, limiting the number of times we have to pass through the vineyard significantly, reducing our carbon footprint as well as reducing compaction of the soil caused by driving down the vinerows too many times with the tractor.
Another significant job in the vineyard in Spring is called “suckering.”Â This is when we – well, mostly Arnulfo – remove shoots and leaves from the vine.Â Some of these are classic suckers, as those with fruit trees might know, that grow up from the base of the vine.Â In addition, when suckering we select the shoots that we want to bear fruit this year.Â This controls vigor and reducing the production of grapes from each vine, limiting yield.Â Suckering has several other purposes as well.Â We pull some leaves from the vine, which results in better sun access and airflow.Â This is important to combat mildew, which can harm the young green growth of the vine, and – if it gets established on the vines now – can result in bunch-rot prior to harvest, which none of us want!Â Finally, when suckering, we make decisions about where we want to guide the growth of next year’s positions.Â Whew – lots to think about when it looks like we’re just pulling a few leaves and branches off the vines!
To watch a fabulous video about these processes, featuring Paul Hobbs, watch Winegrape Chronicles, vol. 2, made by the wonderful Sonoma County Winegrape Growers.
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