OW, I have some direct experience with this problem in that the very disappointing September we had affected my winemaking plans this year quite severely. I was planning to do a dry Concord as in 2002 and the early part of summer seemed quite promising for a good-quality crop. As August drew near, though, I was surprised by the cold nights ... as September came on, however, I was appalled by the constant rain and cold, and just about the worst possible weather imaginable at the most critical time for fruit quality development.
As it stands, a local grower had some slightly overcropped but otherwise decent Cayugas (white, non-foxy hybrid grapes). I decided to pick those and make white wine from them. The wine is almost finished, but I haven't tasted it as yet.
There have been rainy vintages in Ontario in the past that surprised me with the overall quality of the whites - but I don't hold out too much hope for '06 across the board, unfortunately. I think rot must have been severe in vineyards this year. Time will tell, however.