Dennis from Glenwood, Ia writes
Crabgrass seeds begin to germinate when soil temperatures reach 55 to 60 F and continue to germinate over several weeks from spring into summer. Pre-emergent herbicides such as Dimension 2EW normally should be applied in early to mid-April in southern Iowa, mid-April to May 1 in central Iowa and late April to early May in the northern portion of the state. Pre-emergent herbicides should be applied when the forsythia blossoms start dropping or when redbud trees begin to bloom. I found a great article here by Iowa State that further explains.
Answer last updated on: 01/31/2017
