Tolerance of Tall Fescue to Sulfentrazone When Applied with Various Fertilizers and Three-Way Herbicides.

When managing tall fescue (Festuca arundinacea Schreb.) in home lawns, lawn care operators commonly apply combination herbicides tank-mixed with various fertility regimes to reduce site visits.  However, research has shown that applications of sulfentrazone tank-mixed with urea can cause injury to tall fescue.  Research was conducted to determine the tolerance of tall fescue to sulfentrazone with various fertilizers applied independently (30-45 minutes after herbicide application) or tank-mixed together.  Treatments of Dismiss (sulfentrazone) at 0.42 kg a.i. /ha and Echelon (sulfentrazone plus prodiamine) at 0.84 kg a.i. /ha were applied with urea, ammonium nitrate, or 20-20-20 at 24.47 kg N/ha to a mature ‘Confederate’ tall fescue stand.  Dismiss and Echelon plus urea injured tall fescue the greatest (> 20%) regardless of independent or tank-mixed application.   Dismiss plus ammonium nitrate or 20-20-20 applied independent or tank-mixed moderately injured tall fescue (> 10%).   Echelon plus ammonium nitrate or 20-20-20 had minimal injury (< 10%) regardless of independent or tank-mixed application.  These data indicate that fertilizers should not be applied with or shortly after applications of sulfentrazone.  An additional experiment was conducted to determine the tolerance of tall fescue to sulfentrazone tank-mixed with urea, three-way herbicides, and/or chelated iron.  Treatments includes Echelon at 0.84 kg a.i. /ha with or without urea at 24.47 kg N/ha, Trimec Classic or Triplet (2,4-D, MCPA, plus dicamba) at 4.125 L/ha, and 4-4-5 chelated iron at 6.4 L/ha.  As seen in the previous study, treatments containing Echelon tank-mixed with urea injured tall fescue the greatest (> 23%); however, injury was significantly reduced (< 15%) with the addition of chelated iron.  These data indicate that chelated iron could be used to safen the application of urea and sulfentrazone on tall fescue home lawns.