When is it safe to remove row covers in NW Washington that are used to prevent Carrot Rust Fly damage!
I'm pretty sure, ughman, that the general suggestion for carrot rust fly is to leave the row covers on until you pull all of the carrots.
Try sprinkling used coffee grounds around (or with) your carrots--works like a charm!
Leave the row covers in place until you harvest. Some studies indicate the Fly is quite active until about mid November in Washington.