can you give us a link for this procedure???

if your ash has the borer ... what good is a topical spray ...

or are you asking if it will soak thru the bark into the functioning part of the tree???

ken

best explanation is this youtube video.

http://www.youtube.com/watch?v=GpRl2LEL428

is there something special about the lower 4-5 feet of the trunk?

I'd just at soon get up into the tree to guarantee the product gets to the bugs.

I saw that a lot when I was a kid in the 60s - the purpose was to stop the bugs that (supposedly) crawled up the tree - tent caterpillars were a particular target (I still hate those things). The hope was that they would pick up the insecticide on their way up the tree and croak. Given the number of tent caterpillars at the time, I don't think it was very efficacious.

Safari is a systemic insecticide that can be applied as a basal bark spray. The chemical is absorbed through the bark and is transported upwards in the active tissues of the tree. Spraying the lower trunk is sufficient to get enough into the tree to be effective.

Here is a link that might be useful: Anulewicz et al. 2009