The best organic remedy is to catch the infestation early, and cut each bag off the plant. This may be impossible if the plant in question is a large tree. On this case, Bt, spinosads and pyrethrins are organic controls, but must be applied in May or June, when larvae are small and susceptible. After they build their "home" they are less susceptible to pesticides and other controls. In any case, cut off the bags you can reach before you spray.
And Happy St. Pat's Day, the traditional day to plant your peas!