Effect of Preemergent Herbicide Timing on Safety and Germination of Native Grasses.

Research was conducted to evaluate the effects of herbicides and application timing upon warm and cool season native grasses commonly sown on Southeastern US golf courses.  The experiment was a completely randomized design (4 replications).  Treatments included atrazine (1.12 kg ai ha^-1), prodiamine (0.596 kg ai ha^-1), dithiopyr (0.56 kg ai ha^-1), isoxaben (1.12 kg ai ha^-1), pronamide (1.16 kg ai ha^-1), pendimethalin (1.66 kg ai ha^-1), metolachlor (2.78 kg ai ha^-1), simazine (2.24 kg ai ha^-1), topramezone (0.037 kg ai ha^-1), liquid and granular applied oxadiazon (2.24 kg ai ha^-1), indaziflam (0.0327 kg ai ha^-1), flumioxazin (0.286 kg ai ha^-1), mesotrione (0.28 kg ai ha^-1), dimethenamid (1.68 kg ai ha^-1), and a non-treated check.  Grasses evaluated were Andropogon gerardii, Elymus canadensis, Elymus glabriflorus, Elymus virginicus, Panicum virgatam, Schizachyrium scoparium, Sorghastrum nutans, and Tridens flavus.  Plants were grown in 53 cm³ conetainers containing native soil.  Treatments were applied preemergence and early postemergence (4 weeks after germination).  In the preemergence study, 10 and 8 seed, warm season and cool season grass, respectively, were sown and covered with 14.79 cm³ (0.6 cm depth) of soil before application.  Treatments were applied in a broadcast carrier volume of 374 L water ha^-1.  Granular oxadiazon was soil applied on an inert carrier.  Visual injury was evaluated biweekly.  Root and shoot dry mass, shoot length, and germination were recorded 8 weeks after treatment (WAT).  Means were separated by Fisher’s protected LSD (alpha=0.05).  When applied preemergence, mesotrione increased germination of Elymus virginicus 28% relative to the non-treated.  All other preemergence treatments resulted in similar emergence to the non-treated.  At early postemergence timing, atrazine and simazine injured all cool season grasses, Andropogon gerardii, and Schizachyrium scoparium greater than 65% and up to 100% 4 WAT.  At the same timing, metolachlor injured Sorghastrum nutans and Tridens flavus 75%; while prodiamine, pronamide, isoxaben, and pendimethalin resulted in limited injury to the warm season grasses.  Results indicate multiple preemergence herbicides may have utility in native grasses.  However, herbicide safety at early postemergence application timing was specific to grass species. 

 Results from a repeated study will also be discussed.