My trellis is covered in unripe green grapes. It looked as if we were going to have a bumper crop. One morning I saw that most of the grapes were covered in a powdery white substance. Over the next few weeks the grapes shriveled up. I have no idea what happened here. The previous year we had beautiful, sweet purple grapes.
Hardiness Zone: 4a
By Este from Mississauga, Canada
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It looks sort of like what happened to my fig tree several years ago. The white spread to the bush itself and ended up killing it, we thought. A nurseryman told me later that it was Bordeaux fungus. It affects grapes, figs, some other things. I believe that Ortho makes a spray for Bordeaux fungus, just read some of the labels. Ask at a farm or nursery center what they have.
If spraying with liquid soap/water doesn't work you might consider that it isn't mildew.
The white powder is a fungus called oïdium. Here is a natural remedy that should stop the fungus propagation : spray leaves and grapes with 0.5% sunflower oil emulsified in water.
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