Mark Renz Extension Weed Scientist, Agronomy Department, University of Wisconsin-Madison
Knowledge of weed emergence is important as it can help in the selection and optimization of early season weed control. While typically weed emergence is consistent from year to year, the past four years have been highly variable. Weather patterns drive these differences, and this spring’s weather has been far from typical. So how has the cold, then hot, then wet spring impacted weed emergence?
The short answer is about a one week delay. Of the 22 CCA listed weeds, only five species have yet to emerge. While these five species were all emerged at this time last year, many of these species typically don’t emerge until the middle of the May and I expect to see them germinating this week. For example crabgrass was not present in the field, but I have observed it emerging from soils in urban areas next to the sidewalk. This is a great example of how site specific emergence can be.
Below are some interesting species specific observations from Arlington Wisconsin. Note that the earlier emerging species like Canada thistle and kochia are close to a month late while later emerging species like yellow nutsedge and giant foxtail are a week or less late. Will this persist throughout the season? Ask me in September……