Late spring in the Yangtze River Delta. A time of glorious weather before the sultry summer. Tea in classical gardens. Flowering trees have bloomed, and are now in full leaf. On the golf course, grasses are growing a little more rapidly day by day.

That sets the scene for this mystery. A bermudagrass tee, in late spring, in the Yangtze River Delta of East China. In the previous 2 weeks, the lowest temperature was 10°C, and the highest was 31°C.

On the tee, a strip of green. Here is a look from another angle.

A closer look at the turf in the green stripe is here.

And this is what the turf looked like outside of the green stripe.

The mystery is this: what caused the green stripe on this tee? 

Congratulations to Jason Goss who got this one exactly correct:

@asianturfgrass they have a skip when they sprayed for transition back to warm season turf?

— Jason Goss (@gossturf) August 1, 2014

I think the key for this was recognizing the season and climate. With that type of climate, it is common to overseed bermudagrass tees. But one wants to ensure the bermudagrass can grow with no competition from perennial ryegrass for more than 100 days in the summer. That is necessary to keep healthy bermudagrass. Thus, on this high traffic tee, Monument herbicide (trifloxysulfuron) was used to remove the ryegrass, which will allow the bermudagrass to grow with no competition through late spring and all through the summer.

For more about this technique, see the Removing Overseeded Perennial Ryegrass from Bermudagrass Turf fact sheet from the University of Tennessee. 

Partial credit for a correct answer to @GreatManDan and @PenderSuper, who identified the herbicide skip and ryegrass involvement.

Thanks to everyone who sent their answers. For other turfgrass mysteries, click here.