These aphids are regular visitors to the test vineyard. I haven't read or heard much about their being a serious pest, but we had an explosion in the population after three days of serious rain in June and all growing shoot tips were covered with aphids and their ant minders. Growth appeared to be stunted, and then I started noticing other damage and defoliation.
I won't blame it all on the aphids, but they seemed to represent heightened insect activity. I've never sprayed insecticide before, but I finally broke down and applied a dose of Sevin. I'd love to grow as sustainably as possible, and it's disappointing to use the more toxic chemicals. But it's worse to watch a crop suffer.