Along #18, you can see patches of the brown "grass."
More patches between #10 tee (foreground) and the fairway. Most of this area was Yellow Nutsedge.
The left side of #13 fairway. You can see a greener line to the left of the cart path. This was an area where the contractor had a problem with the irrigation line. They had to dig it up after it was originally seeded and hand spread the seed after fixing the irrigation. This meant they put down more seed per square foot. The resulting turfgrasses came in thick enough to discourage the weeds from germinating.
A closer picture. The brown, spider-like clumps are crabgrass. This form is how it got it's common name.
Here is a much closer image. You can see the turfgrasses are growing amongst the dying crabgrass and are looking very healthy.
The brown clumps here are sedges.