Check out the MSU gypsy moth/spongy moth website.  There is quite a bit of information there about GM outbreaks. Outbreaks usually last 3 or maybe 4 years, but a virus disease (NPV) will eventually cause the outbreak to collapse.  For a DIY control option, soapy water will kill the caterpillars.  It's best if you can knock them into a bucket and let soak in the soapy water (e.g., Dawn dish soap) for a couple of days.  You can also put a high pressure nozzle on the end of a garden hose and blast as many larvae as possible off the tree trunks, sides of your house, etc.  Then step on as many as possible - if the high P spray doesnt kill them, your foot should.  Be careful with oils or vinegar or other so-called DIY options - some of those can harm the tree or at least burn the leaves.