Effect of Edaphic Conditions on Hybrid Bermudagrass Injury Following Indaziflam Applications.

Since indaziflam’s 2010 US registration, sporadic cases of hybrid bermudagrass (HB; Cynodon dactylon L. x C. transvaalensis) injury have been reported; however, causes are not well understood.  Field research was conducted to elucidate the effects of various edaphic conditions on HB growth following indaziflam applications.  The objectives of the research were to evaluate the effect of soil organic matter (SOM) and soil volumetric water content (VWC) prior to (PRE), and following (POST) fall-only and fall-plus-spring indaziflam applications on HB growth.  The effect of SOM was evaluated at two levels, 5.5 and 1.4 % w w^-1 at the soil surface in high and low SOM, respectively.  The effect of soil VWC was evaluated PRE (2 wk prior to application) and POST (6 wk following application) by covering low VWC plots during irrigation/precipitation events.  High VWC plots received > 3.8 cm H₂O wk^-1.  Following indaziflam applications at 50 or 100 g ai ha^-1, data collections during non-dormant HB periods included visual cover and injury (0 to 100 %), normalized difference vegetation index (0 to 1), and cover determined via digital image analysis (0 to 100 %).  Further, soil cores were collected from plots 70 and 98 d after treatment to quantify indaziflam-soil mobility and bioavailability.  Overall, data suggest HB cover was reduced most in low SOM.  Soil VWC did not adversely affect HB cover in high SOM; however, PRE/POST high VWC reduced HB cover in low SOM.  Bioassay data suggest the increased adverse effects on HB growth in low SOM – high VWC plots was due to increased indaziflam-soil bioavailability, as significant reductions in bioindicator growth were observed at deeper depths than cores collected from corresponding high SOM plots.  Data from this research will aid turfgrass managers to effectively use indaziflam without adversely effecting HB growth.