Cuttings from older American elm....

We've been on our property long enough now to have seen many elm trees succumb to Dutch elm disease. There are, however, a few elderly trees still standing in the midst of what has died and we suspect they may have some natural tolerance or resistance to the disease. Does anyone have experience, or a link to such information, for making cuttings and rootings from older American elm trees.....probably 30 - 40+ years of age? Thanks.