When is a good time to apply a pre-emergent for crabgrass? Does the soil temperature need to be stable at 55 degrees before the pre-emergent is applied? I think according to DAWN the soil temperature in Jamestown is about 46 degrees.
Stutsman County North Dakota
The best weed control for Crabgrass is quinclorac (a post-emergent). The best time to apply is in the spring when the crabgrass is young.
Crabgrass usually begins germinating when soil temperatures are consistently around 55 degree (3-4 days). As the soil warms further, more and more crabgrass seeds germinate. Pre-emergent should be applied before germination starts to maximize effectiveness. There are a few pre-emergent products that will kill very young crabgrass seedlings but most do not. In the Mid-Atlantic we typically apply beginning when soil temps get into the 50s. You can apply before that but you have to consider the persistence of the product you choose. If you apply too early you would have season long control and may have to reapply. We use the window of when forsythia is in full bloom until it reaches about 50% petal fall / when native dogwoods bloom as the typical spring window for crabgrass pre-emergent.