Crossbow Herbicide for Guava / Faya?

[oink]

I can't advise on the Crossbow, but I can blab:
I've never had to eradicate guava. I do know that the best way to get rid of Brazilian Pepper (so called Christmas Berry) is to back up my truck to it, wrap a chain around it and to my hitch, and drive off. Obviously this doesn't work after they get past a certain size. It should work in dirt or Aa but might not work so good if growing in Pâhoehoe cracks.

Pua`a
S. FL
Big Islander to be.