OK Bill, here's the answer I received to your question. Ami
Theodore,
I developed the probe hole method and it works very well. Before you do the holes around the drip line approach, dig into the soil and verify there are roots present there from your trees. If you can’t find feeder roots at the drip line, move closer to the tree and find where the roots are densest in the soils. That’s where you want to make your probe holes. I wouldn’t use a pressure washer. We have seen substantial benefit to fruit trees and many other kinds of trees by using the probe hole approach. The mycorrhiza will not grow into a plant root unless it is near the root and activated to grow by the root exudates. It will spread through the root and out into the soil from the roots. As it contacts other roots, it will get into those roots also. The probe hole approach gets the product onto a lot of roots if you are close enough to the tree.
Best Regards,
Thomas Giannou
http://www.tandjenterprises.com