Both my neighbor and mine had erected a fence along our property.

They had a vinyl fence, and since code specified a fence cannot be directly
built on the property line but must be set 6" back minimum, their fence was
about 8" back. I hated the look of a vinyl fence so I built a wood fence,
also about 8" from the property line.

This leaves a sliver of space about 16" wide between our two fences.

Mysteriously things started to grow inside this sliver, shrubs, and a few
papaya trees shot up and now is about 9' tall with the trunk diameter 3" in
size. Some of the shrubs are starting to shoot up to already taller than
the 6' fence, some things are bulging against my wood fence, nothing serious
yet but if I ignore them it will be serious in a few years.

Obviously we don't have access from the side, but only from the top. The
area is about 110' long.

Is there something I can sprinkle down this space and kill off what's in
between? I cannot use RoundUp because my understanding is RoundUp you need
to spray to the root area and I only have access from the top side.

Thanks,

MC