Yesterday, I was advised to spray Copper Spray to treat well advanced fungus, possibly powdery mildew that has become very evident in all 20 of my mature (possibly 20 years old) grape vines. This I did following the instructions of 3 tablespoon to 10 litres of water. However, because even the vines climbing up the building were infected I decided to spray one that grows under a plastic roofing outside our front door. The immediate effect was drastic. All the leaves have wilted and appear to be dying. Today there is no sign of recovery. I have just moved to the property and many of these vines have been neglected over recent years so I pruned hard in Spring. However the one outside our front door we didn't prune so hard. Is there anyway to salvage this damaged plant? It looks terrible after less than 24 hours. Look forward to some much needed advice. Thank you Vic
I am of the opinion that powdery mildew cannot be eliminated after it has taken hold. I encountered it two years ago on several plants, and simply left it alone, and the following year everything was fine. Prevention to some degree is the best solution. When watering plants, don't wet the foliage, unless the Sun can immediately dry the vegetation. Of course, if you live in a wet zone this can be a major problem, and one has to live with it. The effects of powdwry mildew are certainly a minor catastrophe.
"Although not listed on the label, grape varieties Merlot, Sauvignon Blanc, Chancellor, Vidal, Concord, Elvira, and Niagara are considered copper sensitive" from: http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2006/08hrt06a4.htm Ralph
Ralph is correct, I have used dormant sprays (lime sulphur and dormant oil) and regular sulphur sprays every 7 to 10 days during the growing season up to 30 days before harvest.
Vic: As for what to do: nothing. If your vine is going to survive, it will push out new shoots and the damaged ones will die back. If it gets going, you can tidy it up if you wish after it has had a chance to develop some significant new foliage. Prune it as usual when it is dormant this coming winter even if it looks dead. Grapes are very resilient. Ralph
I disagree with Ralph on this one if you do not PREVENT powdery mildew it can seriously affect the quality of your berries (splitting and a sour taste) lower yields and lower sugars In the Okanagan wineries have a less than 3% tolerance some even 0% infected bunches!! They will remove infected bunches prior to pressing. Contact BC Wine counsel they have an great grape management guide I am sure Ontario Grape growers have one as well
Vic & Tobias: My apologies - I was anything but clear. My "do nothing" advice was for the damaged plant only, and only to do with the existing damage. Powdery mildew is a serious economic pest to the grape industry, and even if you are not "industrial" it must be managed to the best of your capability or you will suffer serious crop losses. Almost all control programs will include multiple sprays, plus there are cultural practices that will increase air flow and sun penetration, removal of infected parts (and removal from the vineyard - no composting or chipping for re-use around the grapes), and more. Also to consider is next year: PM produces fruiting bodies in the fall, and these will be waiting for you and your vines next spring, so that is the target of the later spray(s). Next time I'll have my coffee before I post. Ralph
