How does the use of herbicides on farm affect the honey production of a local bee keeper?

Herbicides are often used to kill plants other than those being grown by the farmer. This includes the wild flowers growing in the field margins where there are no crops anyway. As a result there are far fewer flowers for the bees to forage.
It goes against intuition, but it is a fact that bees kept in a city generally do far better and make more honey than bees kept in rural locations because city bees have access to parks and people's gardens with their wide range of flowers, wheras rural bees are now faced with agricultural monocrops and far fewer wild flowers.