Evaluation of herbicide efficacy and application timing for giant miscanthus (Miscanthus x giganteus) biomass reduction

Abstract

Giant miscanthus has the potential to move beyond cultivated fields and invade noncrop areas, but this can be overshadowed by aesthetic appeal and monetary value as a biofuel crop. Most research on giant miscanthus has focused on herbicide tolerance for establishment and production rather than terminating an existing stand. This study was conducted to evaluate herbicide options for control or terminating a stand of giant miscanthus. In 2013 and 2014, field experiments were conducted on established stands of the giant miscanthus cultivars ‘Nagara’ and ‘Freedom.’ Herbicides evaluated in both years included glyphosate, hexazinone, imazapic, imazapyr, clethodim, fluazifop, and glyphosate plus fluazifop. All treatments were applied in summer (June or July) and September. For both years, biomass reduction ranged from 85% to 100% when glyphosate was applied in June or July at 4.5 or 7.3 kg ae ha−1. No other treatment applied at this timing provided more than 50% giant miscanthus biomass reduction 1 yr after application. September applications of glyphosate were not consistent: treatments in 2013 reduced biomass by 40% or less, whereas in 2014, at all rates provided at least 78% biomass reduction. Glyphosate applied in June or July was the only treatment that provided effective and consistent control of giant miscanthus 1 yr after treatment.

Miscanthus×giganteusgrowth and control in simulated upland and wetland habitats

“…Finally, integrated control techniques should be investigated for control of M. × giganteus , as mechanical and biological control methods have been reported to reduce M. × giganteus growth (Barksdale 2016; Barney et al 2012). Barney et al (2012) reported damage to M. × giganteus by an unknown herbivore in lowland riparian habitats to such an extent that it precluded long-term growth assessment, suggesting that herbivory/grazing alone or as part of an integrated management strategy warrants further investigation.…”

“…Barney et al (2012) reported damage to M. × giganteus by an unknown herbivore in lowland riparian habitats to such an extent that it precluded long-term growth assessment, suggesting that herbivory/grazing alone or as part of an integrated management strategy warrants further investigation. Simulated mowing reduced M. × giganteus rhizome production and biomass 59% to 71% at 13 WAT in a greenhouse experiment while increasing shoot density (34%) and aboveground biomass (83%), suggesting that treated plants utilized rhizome starch reserves to increase aboveground growth as a recovery mechanism after mowing (Barksdale 2016). Repeated clipping of aboveground biomass of other perennial rhizomatous plant species has been shown to be a potential control mechanism if clipping is conducted frequently enough to repeatedly reduce plant biomass (Derr 2008; Turnage et al 2019).…”

“…Four of those herbicides (2,4-D [ester: 264, 528, and 1,056 g ae ha −1 ; amine: 0.53 g ai ha −1 ], carfentrazone [18 g ai ha −1 ], flumioxazin [107 g ai ha −1 ], and topramezone [9, 12, 18, and 36 g ai ha −1 ]) had no effect on plant biomass at 4 (Anderson et al 2010;Everman et al 2011;Li et al 2013) or 8 wk after treatment (WAT; Li et al 2013). However, three herbicides (glyphosate, imazamox, and imazapyr) did reduce M. × giganteus in these and other trials, such that further investigation is supported to determine whether these herbicides and others with similar modes of action will be useful for wetland resource managers trying to inhibit spread or colonization of M. × giganteus (Anderson et al 2010(Anderson et al , 2011bBarksdale et al 2020;Everman et al 2011;Li et al 2013).…”

“…Li et al (2013) reported foliar imazamox applications (79 g ae ha −1 ) reduced height of M. × giganteus 67% and 73% compared with nontreated plants in nursery field plots at 2 and 4 WAT but had no effect on aboveground plant biomass at 4 or 8 WAT. Finally, Barksdale et al (2020) found that foliar imazapyr applications (56, 280, and 560 g ae ha −1 ) had no effect on M. × giganteus biomass at 52 WAT in field plots near Louisville, MS, while applications (560 g ae ha −1 ) to field plots near Starkville, MS, reduced aboveground biomass 65% at 52 WAT.…”

“…In a greenhouse experiment, Everman et al (2011) found that foliar applications (0.84 kg ae ha −1 ) of glyphosate reduced M. × giganteus aboveground biomass 65% at 4 WAT compared with nontreated plants but also found that belowground biomass was unaffected. Finally, Barksdale et al (2020), reported that glyphosate (1.3, 2.2, 4.5, and 7.3 kg ae ha −1 ) applied in 2013 reduced M. × giganteus aboveground biomass 85% to 93% at 52 WAT in field plots near Louisville, MS, and similarly reduced aboveground biomass 78% to 100% the following year (2014) in plots near Starkville, MS.…”