Chemical Termination of Winter Fallow Cover Crops in Mid-South Production Systems.

Frequently, cover crops grown during the winter fallow season in the southern Mid-South are not terminated by winter conditions.  This results in either the successive crop being planted into heavy residue or requiring chemical management of the cover crops in the spring.  As the heavy residue can increase pest problems with successive crops, chemical management is typically the preferred option.  A study was developed to evaluate three cover crops and four herbicide active ingredients.  The cover mixes utilized centered on the use of the Tillage Radish®.  It was evaluated with crimson clover and ryegrass, separately, in addition to being evaluated as an individual cover crop.  The herbicide termination program was composed of glyphosate and 2,4-D, paraquat, thifensulfuron and tribenuron (Harmony Extra SG), as well as rimsulfuron and thifensulfuron (Leadoff).  Percent terminated tissue was used as the primary indicator of burn-down efficacy.  Digital images were taken at a static 1 meter above the crop canopy, and were collected every 14 days.  These pictures were analyzed with the WinCam picture analysis software.  Overall, all chemical burn-downs resulted in over 75% terminated tissue within the 8 weeks after application.  However, the major differences resulted in the amount of time to successfully terminate the tissue and the percent active vegetation at the proposed planting period.  Paraquat was successful at terminating vegetative tissue within 2 weeks of application; however, there was increased green biomass late due to incomplete termination of the cover crop mixtures.  This reestablishment of cover crop biomass was not seen when Tillage Radish® was evaluated individually.  In general, all the herbicides evaluated were successful at terminating above ground biomass within the sampling period.  However, the most critical issue was timing.