Hello Stan & All,
Stan wrote:
 If the hardwood trees are types where bees work the pollen, then it could
it
 be big problem.  If not (like elms, I *think*) then unless there are
 flowering weeds under them, it might not be a problem.  The quote is
 interesting because it shows that the chemical is persistent for years.

The Elms are very popular to the bees for pollen(American Honey Plants pg.
141)
Sorry Stan but bees gather pollen from Elm and also nectar from Ulmus
Parvifolia  and Ulmus alata  (American Bee Journal Jan. 1947) Possibly they
gather some nectar from other elm but these two above have been noted for
producing a surplus.
Bob