It appears that $1.00 cotton may be chasing a few cows out of the pasture! There have been a number of calls coming in about planting cotton in old bermuda grass or switchgrass pasture.  My first response to these calls is it would have been better to try to control warm season perennial grasses in the fall. In the fall systemic herbicides can be very effectively translocated to the crown of the grass.  Established bermuda grass and switchgrass can be very hard to control in the spring.  During the spring carbohydrates are being moved from the crown to the stems.  As a result translocating herbicides like glyphosate or clethodim (Select Max) are not effectively translocated to the roots.  Often glyphosate will kill the top portion of the plant but new growth from the crown quickly regrows.  Therefore a persistent sequential approach is the best management option.

Dr. Neil Rhodes who has been doing the pasture and weed control research in switchgrass has made the following suggestion in removing unwanted bermuda grass or switchgrass. First, plan to mow the grass to better expose the new growth to a herbicide application.  Then wait for some new growth.  After several inches of regrowth are apparent apply 44 ozs/A of Roundup PowerMax or 64 ozs/A of a generic glyphosate. Then be prepared early post emergence in crop to tankmix some clethodim in with glyphosate to remove any escapes.  Depending upon the level of control a follow up application of glyphosate may be necessary to control any persistent regrowth.