I've never heard of such a thing for this application (willing to be corrected).

NAA is an auxin. A rooting-growth hormone. When you purchase such products, you'll either get ABA, IBA or NAA.

Dan

What does that mean in LAYMANS terms, please.

NAA is not a growth inhibitor.

It is, in fact, a growth regulator. But not the way you want.

AFAIK crape myrtle suckers are a way of life unless there has been a new product introduced since I had my practice.

Dan

Here's info on Monterey Chemical product called Sucker Stopper, the active ingredient NAA.

http://www.montereylawngarden.com/faqs/suckerstopper/

Applied to the newly cut suckers, it slows the frequency of further suckering.

Here is a link that might be useful: product w/ active ingredient NAA

thank you