Goosegrass (Eleusine indica L. Gaertn.), a weedy C4 grass species throughout much of the world, is problematic to control selectively with POST herbicides within ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy] stands (Lee and Ngim, 2000; McCullough et al., 2016; Mudge et al., 1984). Classified botanically as a summer annual, goosegrass plants are eradicated by the first killing frost. However, in tropical regions, goosegrass behaves like a perennial, continuing to tiller year-round as a result of the lack of frost. Also in tropical regions, year-round seed germination leads to plants with varying maturity, resulting in inconsistent preemergence (PRE) and POST control efficacy.
In recent years, reduced performance by certain herbicides (e.g., foramsulfuron), cancellation of goosegrass-specific herbicides (e.g., diclofop-methyl), and cancellation and/or severe use reductions of other herbicides (e.g., MSMA) have limited the options end users have for satisfactory control and maintenance of acceptable turfgrass quality. Currently available herbicides (e.g., topramezone, metribuzin) with activity on goosegrass also often result in unacceptable injury (bleaching) to the desirable turfgrass species. Developing management techniques to reduce turfgrass injury while maintaining herbicide efficacy is imperative for effective POST control of goosegrass within turfgrass stands. Immediately incorporating products via irrigation, or tank-mixing products such as chelated iron (Fe), could reduce turf injury while maintaining control efficacy. The current study focused on turfgrass injury only. Kerr and McCarty (2017) noted little reduction in goosegrass control efficacy of topramezone and carfentrazone + 2,4-D + dicamba + MCPP when irrigated immediately at the same rates used in the current study.
Topramezone (Pylex Herbicide 2.8C; BASF Corporation, Research Triangle Park, NC) and mesotrione (Tenacity 4L; Syngenta Professional Products, Greensboro, NC) are 4-hydroxyphenylpyruvate dioxygenase inhibitors absorbed through roots and shoots (Brosnan et al., 2014; Elmore et al., 2011a). Simazine (Princep 4L; Syngenta Professional Products, Greensboro, NC) and metribuzin (Sencor 75DF; Bayer Crop Science, Research Triangle Park, NC) are photosynthetic (PSII) inhibitors (Nimbal et al., 1996). Simazine is absorbed through the roots; metribuzin is absorbed mostly through the roots (Abusteit et al., 1985; Sheets, 1961). Carfentrazone-ethyl (shoot-absorbed) plus 2,4-D (root-absorbed) plus dicamba (root- and shoot-absorbed) plus mecoprop (mostly root-absorbed) (Speedzone 2.2L; PBI Gordon, KS City, MO) is effective for the control of many broadleaf weeds and goosegrass—the only grassy weed listed on the label (http://www.cdms.net/ldat/ld61R001.pdf) (Beck et al., 2014). The site of herbicide uptake is an important factor to consider when developing techniques to reduce turfgrass injury. If an herbicide is shoot-absorbed, immediate irrigation will most likely remove a certain amount of product, thus possibly reducing efficacy. If an herbicide is fully or partly root-absorbed, immediate irrigation could potentially reduce turfgrass injury while maintaining desirable weed control efficacy.
The objectives of the trials were 1) to evaluate turfgrass injury after the use of POST goosegrass control options and 2) to assess whether irrigating immediately after herbicide application reduces turfgrass injury on mature stands of ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy].
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