I had this idea, though I'd post it here. I'm amazed at the lack of useful robots in this day and age! I think this one could work.
Kudzu is a big problem down south. Fields are overun with it and pesticides don't kill it. Yet, constant cutting of the vine will eradicate it. Here's a problem a robot could handle very well.
A spider type robot that could scan a 1 foot square, find a vine, and cut it, then move on, would be very useful to kill kudzu. These bots could be rented out for clearing fields. They could be given GPS boundaries to keep them in the field. No need to distinguish between kudzu and other types of plants, because kudzu overuns whole landscapes. When they are done, call them back into the truck and move on.
Let me know when you make em! :)