Ryegrass appears to have escaped burndown in a number of fields that have been planted to corn. In most cases the ryegrass escaped a glyphosate plus dicamba burndown. The reason for the lack of control is the continued evolution of glyphosate-resistance in our ryegrass population as well as dicamba decreasing the effectiveness of glyphosate on ryegrass.
The question on how to control ryegrass in a standing corn crop really has no “sure fire” answer. If the corn hybrid is Liberty Link then Liberty at a quart rate can be effective. Tankmixing in a quart of atrazine with the Liberty can improve the control. Please keep in mind when utilizing Liberty in corn applications in late April or early May is that air temperatures can be too cool for Liberty to be effective. In order to get the best ryegrass control with Liberty, try to pick a warm spell where temperatures are in the mid-80s and apply it during the middle of the day. The other option is Steadfast Q which can be effective on ryegrass even at cooler temperatures. The catch is that some ryegrass in the state is ALS-resistant so Steadfast Q will not be effective in those cases.