Aphid-infested tulip tree

It appears we have an aphid problem on our 50 foot Tulip Tree. It is causing the leaves to turn colour already and it looks like fall on my front lawn. At this point, we probably won't do anything as the leaves will start to fall soon anyway, but is there anything we can do next year to prevent this problem? Preferably using organic methods. This is our first year in this house, so I'm not sure if this occurs every year. We're out in Langley, BC. more...