Hi Dave; Worm cast are really not hot like chicken or pig-horse manure. If your plants damped off from putting on the worm castings it may not have been finished enough and still had some breaking down to do. This some times makes some molds and yeasts that produce the "hot" chemical compounds that will cause plant to give the indication that it has had too much chemical contact in the form fo amonia burns. Worm cast usually produce a chemical ratio of 1-1-1 which in reality will not burn plants even in direct contact.