I have been watching for the first crabgrass plants to emerge for each of the past 40 springs. The reason for my interest in this is that I always have some kind of crabgrass treatment going out each spring and I don’t want to miss germination. In Ames, the crabgrass usually germinates by about May 1 and I tell people to try to get their preemergence herbicides out mid-April. It has amazed me over the years how consistent that date for crabgrass germination has been. There have been warm springs when one would expect early germination and cold, late springs where late germination would be expected. However, each year the crabgrass emerges around May 1,
This spring was unusually cold and we still had snow into late April. The weather service tells us that it was the coldest April on record. Yet, on May 2, 2018, the first crabgrass began to emerge at the research station.
In the picture, you can see some knotweed that is beginning to expand. Knotweed, which emerges in late March, is often mistaken for crabgrass in early spring (see the blog from March 23, 2012 and May 29, 2012).It does look like a grass when it first emerges and does not appear to be a broadleaf species until it begins to expand. The crabgrass in this picture is to the right and left of the pen. It has a wide, pointed leaf and is often a light green color at emergence.