Rootone
is not the only product you can use. There are many, and probably
other will work better than Rootone.
Search
in Altavista for "rooting hormones" - include the quotes
and you will find at least 10 different brands of hormones made to
propagate cuttings. If you find something better for hybrid poplars,
let me know.
Right now I am testing Hormodin-3. This product was suggested by the US Forest Service. It comes only on 8 oz cans ($25) and can be ordered from the manufacturer E.C. Geiger Inc at (800)443-4437