The Story of Winter Annual Weeds and What Can I Do?
Is all that green in my harvested soybean field volunteer soybeans?
At first glance from a distance it sure looks like it. A closer inspection may reveal something much different. This is the time of year for “Winter Annual” weeds to germinate and grow. Pictured below are (3) of the five most common winter annual weed species we contend with every year. They include Marestail, Henbit and Chickweed. To round out the “top 5” let’s include Field Pennycress and Butterweed (not pictured).
Figure 1: Henbit and Chickweed
Figure 2: Marestail
Why are they called “Winter Annuals”? It is because these species germinate and begin to grow in the fall under cooler temperatures, lie in wait during the winter and are the first we see green up in early spring that eventually grow to maturity and produce seed. With the exception of Marestail, winter annuals die off as spring temperatures increase but not before potentially creating problems with tillage and planting. For years, winter annuals were tied to being an issue in no-till production; however, reduced tillage growers are also experiencing greater winter annual weed pressure including the very hard to control Marestail. Management typically involves a timely spring burndown program combined with a residual herbicide. “Timely” is underscored in the previous sentence as this a one-shot to do it right as Marestail again is very difficult to kill after it begins to bolt.
A better option is to control these weeds in the fall prior to freezing temperatures which will stop the problem before it has a chance to get worse in the spring. All (5) of these weed species are easily controlled in the fall with a recommended herbicide application. Please consult your United Prairie Sales Agronomist on how best to treat high pressure winter annual acres this fall.