James writes
I'm guessing I will have to spray more than once.
Yes, LambdaStar UltraCap 9.7% is labeled for cluster flies. It is recommended that you apply in late summer or early fall before flies are observed alighting on surfaces. Apply thoroughly on siding, under eaves, and around windows and doors. Do not spray to the point of runoff. This can be applied every 30 days outdoors. We also have a great guide here on "How to Get Rid of Cluster Flies" that might help.
Answer last updated on: 04/12/2019