Is "plant matter" weed?
Mostly no. Dead leaves that were just lying on a trailer without getting cleaned in advance and bits of decorative plants that broke off are probably the worst offenders.
You think they’re leaving any of that behind?
If it was that'd be an absurd amount of weed being left behind to make a mark on the map.
Mostly no. Dead leaves that were just lying on a trailer without getting cleaned in advance and bits of decorative plants that broke off are probably the worst offenders.