Thanks trader and KC.

I took your advice and made some inquiries at my local yard and garden
center. They recommended RoundUp Weed and Grass Killer "Concentrate Plus".
It comes in a 16 oz. white bottle with a red cap. The guy who helped me
told me the same thing -- brush it on at full concentrate (undiluted) to the
freshly cut stump with a paint brush. He added that drilling holes or
cutting grooves in the stump and applying the RoundUp inside might help it
penetrate and kill better.

I'll try this in a couple days.