This morning I talked to Plant Heralth Care, Inc., Pittsburg, PA.
About 5 years ago I purchased their trade marked product, "MycorTree" which is a dried innoculant of both endo and ecto fungi for trees. They told me the life expectancy of the ecto portion is about 10 years when stored under refrigeration as I did mine. The endo portion about three years.
This product comes in 3 oz. packets when mixed as a slurry will treat up to 100 small bear root trees. This is done at planting. I have ordered 10 packets but only need about 2. The smallest order is 10 packets at about $95. You can visit their web site at planthealthcare.com