Wednesday Search Challenge (3/13/13): How much death at the roadside?

Last week I was driving down a scenic California highway with my friend Pat who asked a great question:  “Why is there always a brown stripe of dead or missing grass at the edge of the highway?”  He's right--take a look. 

As we drove out of the Sierras and into the Central Valley we saw mile-after-mile of either brown grass, dead grass, or a zone of no-grass at all along the edge of the road.  It’s the kind of thing that you don’t even notice until someone points it out to you.  There’s a constant zone of death at the highway’s edge. 

To add to the mystery, when we turned onto a side road, we noticed that the grass came right up to (and in cases into!) the edge of the road.  Take a look at a roadside near where the above images were taken... the grass grows right up to the edge of the road.  

So while we’d been talking about the possible toxic effects of asphalt on grass and weed growth, this pretty clearly wasn’t the case.  There’s nothing about tar or asphalt that kills the grass.

A few minutes later, we saw the killers:  there was a truck driving slowly down the road with a man dressed in a white jump suit, clearly spraying weed killer at the edge of the road. 

When we got back onto the main road, the brown, dead zone picked up again and Pat asked today’s research question: 

1.   Just how many pounds of herbicide are sprayed along California roads each year?
 2.  And, of course, just how toxic is this herbicide?  (Should I be worried as I drive up and down these roads?  Should I be worried if I ride my bike along these sprayed roads?) 

To tell you the truth, I haven’t yet answered this question myself, so I don’t know ahead of time how easy (or difficult) this will be. 

To make things clear—let’s try to discover how much herbicide is used on California state roads. 

As usual, it’s an open Internet. Let’s dive in and see what we can find. As you discover things, post what you find to the comments stream below, and we'll collectively figure this one out.  

I usually hold back the comments until later in the day, but since this question could take some time to figure out, I’m going to let the comments become visible fairly quickly in the hope that we’ll be able to help each other out.  

Please let us know what your thought process is as you search for the answer.

And, as always, let us know how long it’s taken you to find an answer. 

Search on!