How amazing is it to see the soil temperatures go from frozen on March 7th to over 50 degrees on March 16? We sustained temperatures above 50 for 10 days, and have now dropped below 50 degrees at two inches. Crabgrass germinates when soil temperatures are around 60 degrees. The soil temperatures from the Noer are taken under a dense Kentucky bluegrass lawn, but in areas where crabgrass is normally problematic (bare soil, near concrete, etc.), the temperatures were probably 2-5 degrees warmer – enough to start the germination process.
So how will this up and down roller coaster of soil temperatures affect crabgrass pressure in Wisconsin? I wish I knew. Crabgrass may have germinated in some areas, but may not have in others. An herbicide with both pre- and post-emergent activity will be the safest bet in these uncharted waters.