Potential of Myrothecium species as bioherbicides for giant salvinia (Salvinia molesta)
2018
Weaver, Mark | Shearer, Judy | Grodowitz, Michael | Boyette, C Douglas
Giant salvinia, Salvinia molesta Mitchell, is a floating macrophyte native to South America, but since the 1930s it has been spread to areas in Africa, Asia, Australia, and the warmer temperate and subtropical areas of the United States (Jacono and Pitman 2001). This fern has a tremendous growth rate in eutrophic water, forming dense floating mats with biomass production of up to 100 tons ha1 yr1 (Mitchell and Tur 1975, McFarland et al. 2004). Water resources can be degraded by giant salvinia through the competitive exclusion of native vegetation, depletion of dissolved oxygen, and the impeding of navigable waterways (McFarland et al. 2004, Knutson and Nachtrieb 2012). Control measures with limited efficacy include drawdown of the infested waterbody and mechanical control. In-water or foliar application of registered aquatic herbicides can provide effective control (Mudge and Haller 2012, Mudge et al. 2016), but can be difficult to implement effectively in complex infested systems, and selectivity of control and herbicide resistance management must be considered as part of long-term integrated strategies. The release of the weevil, Cyrtobagous salviniae Calder & Sands (Coleoptera: Curculionidae) has demonstrated large reductions in giant salvinia biomass in at least 12 countries, including Australia, Fiji, India, Kenya, Namibia, South Africa, Sri Lanka, Zambia, and Zimbabwe (Joy et al. 1986), and more recently in the United States, including the states of Texas and Louisiana (Tipping et al. 2008). However, weevil efficacy is limited in (Tipping et al. 2008). However, weevil efficacy is limited in more temperate infested sites (Sullivan et al. 2011). A recent survey for fungi with potential utility as biocontrol agents discovered three isolates of Myrothecium roridum as pathogens on Eurasian milfoil (Myriophyllum spicatum L.) in Vermont and dioecious hydrilla [Hydrilla verticillata (L.f.) Royle] in Florida and Texas. Several isolates of M. roridum and Myrothecium verrucaria have been evaluated as bioherbicides against a range of invasive weed species (Hoagland et al. 2007, Lee et al. 2008, Okunowo et al. 2010, Weaver et al. 2016), including ferns (Clarke et al. 2007). We describe here a series of mesocosm experiments to evaluate the virulence of these Myrothecium isolates against salvinia.
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