When to apply pre-emergent herbicide for crabgrass, St. Cloud area.
Thank you for the question. The following information is taken from a University of Minnesota publication: Pre emergent herbicides affect germinating seeds so it's important to remember that it won't work unless the seed has germinated, or started to grow and sprout before it emerges from the ground. Consequently, you want to apply crab grass herbicide just before you think the seed will germinate. The time for this is usually between mid April-mid May. Soil temperatures in the top one inch or so need to consistently be in the 50-55 degree range as measured early in the day. You may want to monitor soil temperatures this year for guidance since the weather is warmer sooner this year than last. Use this website to monitor the temperatures in your area. It is too cold yet according to the graph.
Thank you for contacting Extension.