It is May 2 and we have a snow storm going on in Ames. Normally, when people ask me for a date by which they should have their preemergence herbicide applied for crabgrass control, my standard answer is to have it down by May 1. The question that I have received most often in the last two days, is whether this cold weather will delay germination.
The expected answer would be that the cold weather will delay germination, however, I have been watching crabgrass germination dates for 34 years here in central Iowa. What I have observed is that the germination date does not vary much from year to year. When we have a warm spring and you would expect early germination, the crabgrass still germinates about the same time (around May 1). When we have a cold spring, like this one, the crabgrass still seems to germinate about the same time. It may be a few days early or late, but not a few weeks.
I am still expecting crabgrass to germinate soon. If you do not have your preemerge down, I would recommend applying it as soon after the snow melts as possible. I put mine on last week.