Broomsedge Release in Bermudagrass from Plant Growth Regulator Use.

Imazapic is used to reduce mowing requirements on bermudagrass roadsides in Georgia.  However, broomsedge populations have increased substantially over the last decade and may have resulted from the use of imazapic for bermudagrass growth regulation.  The objectives of this research were to evaluate (1) differential growth responses of bermudagrass and broomsedge to imazapic,  (2) sensitivity of isolated acetolactate synthase (ALS) enzymes of bermudagrass and broomsedge to imazapic, and (3) broomsedge suppression with imazapic tank-mixtures with herbicides.  In greenhouse experiments, bermudagrass growth was inhibited ~2x more from the nontreated by imazapic than broomsedge.  In laboratory experiments, bermudagrass required ~100x lower imazapic concentrations than broomsedge to inhibit ALS enzyme activity 50% from the nontreated.  In field experiments, imazapic provided no control of broomsedge but tank-mixtures with MSMA provided 81% control at 9 months after initial treatments.  Overall, imazapic inhibits bermudagrass growth more than broomsedge due to differences in target site susceptibility between species.  Results emphasize the importance of MSMA use in roadside management for broomsedge control when imazapic is used for growth regulation.