garymc

Glyphosate will only kill plants when it gets on the foliage. If the foliage of your weed can be leaned away from the banana leaves and you use a coarse spray, you can kill the weed. Glyphosate will travel through the weed and kill it's roots. In order for it to translocate through the plant, the dose can't be so high that the leaves are immediately killed and it doesn't travel through the plant. Spray a coarse spray, not a mist that will drift. You may have to spray it a second time (it works best if you do.) Read the ingredients on your product and make sure it doesn't have another chemical that is active in the soil. I use a piece of cardboard to shield other plants from any drift just to make sure.

edited to add:
If the weed you are talking about is a grass with blades, you can use clethodim, a selective grass killer that won't harm broadleaf plants. I'm assuming that bananas are broad leaf plants and not grasses. I use it around grape vines and blackberry vines for killing grass and I've gotten it on the vines without harm to them. Spraying it on the ground or on plants you don't wish to kill is a waste of the spray and would be ill advised with clethodim, glyphosate, or any other herbicide. I have to edit this. "Any other herbicide" is wrong. Obviously, a pre-emergent herbicide is sprayed on the ground and stays in the soil to kill or prevent new plants from sprouting.