Santa Cruz County (where I live and ride) banned the use of herbicides by county workers in 2005. The result is that 600 miles of county-maintained roads (where I ride) are overgrown with poison oak, thorny blackberry and invasive scotch broom.
It costs about $3,000 per mile to mow down the weeds while herbicide spraying costs about $140 a mile. Only 45 miles of road was mowed last year, leaving roadways plagued with overgrown weeds. Guess where these weeds grow? Yep, into the edges of the roads and beyond, exactly where I want to ride my bicycle. Along some roads, the weeds are so high you can't see down the road.
Some farmers, in the meantime, have taken matters into their own hands by mowing and applying herbicides along the right of ways around their fields.