By Arlenelynn
Canada 
Two well establisted grape vines in ground suddenly, overnight have developed some radom wilting of 4-6ft new growth branches. Weather has been favorable. We are seeing no visiable infestation, and have been growing quite vigorously till now.
26 Jul, 2011
Answers
Damage from water spraying can be complex--it takes extraordinary conditions for it to happen, but it can happen. A likelier candidate in my mind is wind damage, or--if they are accessible to the public--broken branches from animals, or kid's of all ages. The breakage may not be easily visible, involving a crushing of tissues inside the branch, usually where it joins the main structure, when it is bent sharply or twisted.
27 Jul, 2011
It could be downy mildew (plasmopara viticola) related to potato blight. I don't know about Canada but here in the UK both of these are rampant at this time, we spray with Bordeaux mixture.
27 Jul, 2011
Previous question
« Hello all, Following some very good advice on here, I chopped the trunk of my...
Have your vines been damaged by drift from any spraying? even water will damage when sprayed in hot sun. Cut off the damaged canes to a healthy bud.
26 Jul, 2011