Flies on plants and bushes are more of a nuisance than a problem. According to the North Dakota State University Extension Service, flies typically do not pose any problem to plants; they are more likely a problem for you. They hover over blooms and therefore can ruin the beauty of the bush. They can also ruin a cookout, outdoor meal or picnic. If flies are infesting your flowering bushes, fortunately, there are a few measures you can take to get rid of them.
Spray flies with an insecticide labeled to kill flies. Avoid spraying directly on the blooms, and always follow the directions on the label.
Set up fly traps around your flowering bushes. Try sticky fly strips, which can be hung on hooks, or fly traps, which the flies can easily get into, but not out of.
Install a bug zapper near your bushes if they are near your home, where you have access to an electrical outlet.