On March 23, 2012, I put up a blog post about knotweed. This annual broadleaf germinates very early each season and is often mistaken for crabgrass.
At that time, I posted a picture of an unknown weed that had just emerged at Veenker Memorial golf course in Ames, Iowa that had some of the characteristics of knotweed, but did not look like the other knowtweed germinating on the course at that time. This patch did look a lot like crabgrass, but it was clearly too early for crabgrass to emerge. The first picture below is the way that weed appeared on March 23.
I mentioned that I would return later and see what the weed was. The second picture was taken in late May in the same location on the course. It is clearly knotweed. I'm not sure why the newly emerged seedlings looked so much different than the other knowtweed on the course. You can see why people mistake some knotweed for crabgrass each year.
Photo 1. Unknown weed on Veenker golf course as it appeared on March 23, 2012. It had many of the characteristics of crabgrass, but was clearly a broadleaf.
Photo 2. Picture taken in late May on the same location where the first photo was taken in March. It is clearly knotweed.