What are those lines on the greens?

Every two weeks or so we make a spray application to our greens. We use  a Toro Multipro 5800, a 300 gallon sprayer with an 18 foot boom width, and a computer type controller that regulates the nozzle output based on ground speed of the unit. It is a great machine, the best currently available in the industry. When we spray, we don't use a blue dye indicator to show the pattern. It leaves a phony looking blue/green color and the area sprayed is highlighted for several days. The operator driving the spray rig can't see the edge of the last pass made with the sprayer, so an assistant goes along and marks the edge of the last pass.

                                            We use a flagstick and drag it leaving a 18 inch line every 10 feet or so the entire length of the green. It leaves lines for the operator to line up with on the next pass going the other direction.

The lines left behind are shown in the photo below. They are visible for a day or so, but disappear with the next days mowing and don't affect a ball rolled across them.