• By Larry Steckel •
Ready or not, burndown season is here! There has been very little burndown applied to date. Weather permitting, some would like to start corn planting before April 1.
A potential short turnaround time from burndown to corn planting is most problematic in controlling ryegrass, particularly if the ryegrass is glyphosate resistant. There are really three viable options to burndown glyphosate-resistant ryegrass in this situation.
One is sequential applications of paraquat (Gramoxone) applied about 10 to 14 days apart. Another option is clethodim (Select Max) mixed with glyphosate. Finally, a glyphosate + rimsulfuon herbicide (Leadoff/Crusher) could be an effective ryegrass control mixture. All three options have good and bad points to consider before making a decision.
If the paraquat option is used, consider adding 1 lb/A of atrazine to the first application to help improve the consistency of control. Of course, the major drawback to using this option is two paraquat applications are most often needed.
As far as going with Select Max, one must consider there is a plant-back restriction of 30 days for corn after a clethodim application. If burndown is further delayed, there is a supplemental label for Select Max at 6 ozs of product applied no closer than six days before planting.
Where ryegrass is small, the 6 oz/A rate of Select Max mixed with a 1 qt of glyphosate works fairly well. On the other hand, for more well-established ryegrass, the level of control using that low rate of Select Max can be sketchy.
The glyphosate + rimsulfuron mixture can be a very effective ryegrass option. It is also very effective on most winter annual weeds. Rimsulfuron has good residual activity on our troublesome summer annual grasses like barnyardgrass, junglerice and goosegrass.
There are two rimsulfuron formulations sold in Tennessee. The rates to use are 1.5 oz/A of Leadoff or 1.0 oz/A of Crusher. The one drawback to this option would be in fields infested with a good bit of ALS-resistant ryegrass. If that is the case, then the paraquat or clethodim options would provide better control.
Dr. Larry Steckel is a University of Tennessee Extension weed specialist. He may be reached at email@example.com.