We can slow down their spread. I don't think we can stop them completely with our control efforts, but we can have a significant impact in terms of slowing them down and minimizing the impact on the forests over time. Eventually we're going to get some help from Mother Nature to provide some cold weather at the right time of year, which will really knock them back.
We can be very effective, and research has been done that confirms that Alberta's program, combined with industry and government, is effective.