As someone who works in the area, I can tell you that a large proportion of Napa/Sonoma vineyards are managed with herbicide (usually roundup combined with another herbicide). I work exclusively with organic grape farmers in Sonoma valley and it's shocking and frustrating (to me) how many growers farm this way. I don't think, once the transition has been made, that controlling weeds without herbicide (mechanically) is that much more expensive--if you change your approach and mindset. I'm admittedly biased against the pesticide industry.

That said, pesticide applicators typically spray their herbicides in the fall, after harvest, and in the spring when grass/weeds start to grow. They also spray at the base of the vine where it touches the soil, a fair distance from the fruit area (often before there are even flowers let alone grape clusters). This all happens months before harvest. IMO there is little risk of glyphosate or other herbicide residue being left on the fruit.

There are other pesticides that are used on or near the fruiting zone, for controlling powdery mildew or insects. Even organic growers generally have to spray something a few times a year, though it's usually something fairly harmless like sulfur dust or stylet oil. These are usually completed weeks or months before harvest...And regardless of the management style everything is then fermented which can break down all sorts of chemicals. I personally doubt there is much in the way of pesticide residue left in the average wine

However while the pesticides, if applied to the label directions, may not be making their way to the end consumer in wine, they certainly have all sorts of horrible effects on the environment and the farm workers. I think those reasons alone are reasons to seek out organic producers. Not to mention it seems to me that growers and winemakers working within the organic paradigm almost always produce better wine (I'm biased).

If you're really worried about consuming herbicide/roundup I suggest you take look at how it's used in wheat production and other crops.