Question
In New England, if a new area is cleared in the woods, how long should you wait before planting if armillaria is present?

Answer
It may depend on how much "clearing" was done. If the stumps and major roots were clearde then there should be no problem. What I would suggest is that you contact the local State Forestry agency and ask one of their Forester to come out and take a look. This is a free service in most states. They can tell you waht needs to be done if anything. Here is a web link that gives information on armillaria:
http://www.na.fs.fed.us/spfo/pubs/fidls/armillaria/armillaria.htm