If the trunks are healthy, and not rotting or seeping low down near the base, then wait till end of May, mid June, or longer if you can bear it - sometimes when the growing tip at the top of the stem is killed, they shoot partway up the trunk/stem, or sometimes just from the base, or both. If that happens, and there's no new growth at the top, you'd cut back to the point where they're showing new growth.

Agree with bamboo, but i would take the rotting tip and leaves off, cut the infected area away and a method i have used before is to cover the cut over with a large tin, or plastic pot, [secured], and as soon as the weather warms up april/may then remove and new shoots should appear in time, then like bamboo says cut back to the desired growth, and carefull consideration should be taken to protect them in future winters. Julien