Herbicide and Weed Control in a Freshwater Seed Production Field of Smooth Cordgrass (Spartina alterniflora)

Smooth cordgrass (Spartina alterniflora) has been used extensively in habitat restoration and coastal erosion control in both brackish and saline habitats. Smooth cordgrass is a perennial intertidal salt marsh plant native to the Atlantic coast of the Americas (Adam 1990). It forms the dominant part of brackish coastal salt marshes from Newfoundland, Canada, to the Gulf of Mexico, and south to northern Argentina. Effective revegetation of this species is crucial to help reduce land loss. Between 1932 and 2010, Louisiana lost approximately 1,883 square miles of coastal marshes (Couvillion et al. 2011). Without effective intervention, erosion will continue, and an additional 513 square miles are predicted to be lost by 2050. Smooth cordgrass has been used to stabilize newly constructed terraces, re-establish lake rims, and create emergent marsh areas to reclaim large areas of land loss. Current revegetation, using smooth cordgrass, relies on the hand-transplanting of bare rooted stems and potted plants. Direct seeding of smooth cordgrass, using agricultural airplanes, provides an alternative planting technique suitable for a large scale revegetation (Utomo et al. 2012). However, large-scale planting will require a large amount of seed that can only be produced effectively from seed production fields.

Seed production systems of smooth cordgrass can be established over a wide range of environments, since it is a facultative halophyte and has the ability to survive in both freshwater and saltwater. Successful seed production of smooth cordgrass requires optimizing important growing conditions, including controlling weeds. Information regarding the herbicides that can be used in a seed production field of smooth cordgrass, however, is limited. The majority of research reported in the literature is focused on eradicating smooth cordgrass and its hybrid progeny to prevent them from growing outside their native ecological range (Anttila et al. 1998, Daehler et al. 1999, Patten 2002). Glyphosate, fluazifop, haloxyfop (Pritchard 1992, Shaw 1997), and imazapyr (Patten 2002) are among the herbicides used to eradicate smooth cordgrass. Recently, Levy et al. (2013) investigated the effects of 10 herbicides on smooth cordgrass in the greenhouse using sprayed potted plants. The studies identified that 1- and 8-month old smooth cordgrass plants are tolerant to bensulfuron, clomazone, halosulfuron, penoxsulam, and triclopyr.

A seed production field of smooth cordgrass managed in freshwater is very similar to that of rice (Oryza sativa). In this environment, a complex of grass and broadleaf weeds exists. Weed control methodologies that have already been established for water-seeded rice (Webster, 2014) can be used as a model for managing weeds in a smooth cordgrass seed production field. A wide range of herbicides have been identified and formulated for specificity of weed control from aquatic, broadleaf, sedge, and grass weeds. Quinclorac or thiobencarb, for example, are commonly used to control barnyardgrass (Echinochloa crus-galli) (Street and Mueller 1993, Zhang et al. 2005), while aquatic broadleaf weeds and sedges are controlled by bensulfuron (Beaty et al. 1993) or imazosulfuron (Godara et al. 2012). Although smooth cordgrass grows well in freshwater, it is less competitive against freshwater weed populations, such as ducksalad (Heteranthera limosa), spikerush (Eleocharis spp.), cattail (Typha spp.), and bulltongue arrowhead (Sagittaria lancifolia). A seed production field of smooth cordgrass can be established by growing transplants of parental lines in the field. Herbicide applications are required in the first year to keep the weed pressure low while transplants are established. Once established, the production field can be maintained for several years with minimal herbicide applications. The objectives of this study were 1) to determine the effects of 14 herbicides on smooth cordgrass seedlings and 2) to evaluate the applications of the herbicides penoxsulam and bensulfuron for control of ducksalad and the impact on yield.

Table 1.

Formulations and concentrations of 14 herbicide treatments applied to assess their selectivity on Spartina alterniflora seedlings. Recommended rates from formulation labels included for comparison.

We conducted herbicide tolerance studies at the seedling stage in the greenhouse in 2011 using 14 herbicides commonly used in the aquatic systems. Smooth cordgrass seed of ‘PolyC15...