Overview
Goosegrass (Eleusine indica (L.) Gaertn) is a troublesome weed for golf course superintendents everywhere. Individual plants can produce upward of 140,000 seeds that germinate under conditions of fluctuating day and nighttime air temperatures (Chin and Raja 1979, Nishimoto and McCarty 1997). Goosegrass is an indicator weed for soil compaction, in part because it can tolerate low levels of soil oxygen and thrive in environments where desirable cool- and warm-season turfgrasses may perform poorly (Waddington and Baker, 1965). For example, researchers in Florida documented increases in goosegrass cover and density within high-traffic portions of golf course tee boxes and suggested that reductions in turfgrass canopy cover from traffic may render goosegrass more competitive in these environments (Arrieta et al., 2009). Given that many golf courses saw increased play in 2020 with a likely continuation of that trend in 2021 (NGF, 2021), the accompanying increases in foot and cart traffic may lead to goosegrass being more problematic for superintendents in the coming year.
Herbicidal control of goosegrass can be challenging for a number of reasons. Although multiple herbicides from several mode of action groups – e.g., Group 3, 14 and 29 – are labeled for preemergence goosegrass control, appropriate application timing can be difficult to identify. For other summer annual weeds like crabgrass (Digitaria spp.), benchmark soil temperatures triggering emergence (55 F) have been identified and associated with phenological indicators to guide superintendents in making preemergence herbicide applications at optimal timings (Cardina et al., 2011). These benchmarks have not presently been identified for goosegrass. Moreover, instances of goosegrass resistance to commonly used preemergence herbicides such as prodiamine and oxadiazon have been reported (McCullough et al., 2013, McElroy et al., 2017).
In regard to postemergence goosegrass control, the suite of available herbicide options for selective control is somewhat limited. Diclofop – e.g., Illoxan – was a labeled option for goosegrass control in bermudagrass (Cynodon spp.) for many years but is no longer available. Additionally, cases of goosegrass resistance to Group 1 herbicides have been documented (McCullough et al., 2016). Similarly, many superintendents in the southern United States relied on mixtures of metribuzin (e.g., Sencor) and monosodium methanearsonate (e.g., MSMA) for goosegrass control in bermudagrass despite it commonly resulting in temporary injury to desirable turfgrass (Johnson, 1980). Label restrictions on the use of MSMA in turfgrass have limited superintendents’ ability to use this mixture effectively, along with instances of resistance to metribuzin (Brosnan et al., 2008).
Broadcast applications of topramezone (e.g., Pylex) can be made to control goosegrass in cool-season turfgrass and applied as a spot treatment for control in bermudagrass and seashore paspalum (Paspalum vaginatum Sw.) (Cox et al., 2017). However, these applications in warm-season turfgrass cause temporary bermudagrass injury (BASF, 2018). A mixture of carfentrazone (Group 14) + 2,4-D + MCPP + dicamba (e.g., SpeedZone) is also labeled for postemergence goosegrass control in both warm- and cool-season turfgrass (PBI Gordon Corp., 2020). However, label restrictions on application intervals can hamper efficacy in some situations and rates for effective control can cause temporary injury to bermudagrass in summer (Brewer et al., 2020). University scientists are currently working to provide superintendents an effective mixture that maximizes the benefits of herbicides such as topramezone, metribuzin, and SpeedZone for goosegrass control in bermudagrass while mitigating turfgrass injury concerns (Brewer et al., 2020, Carroll et al., 2020).