Effects of Various Herbicides on Smooth Cordgrass (Spartina alterniflora) Seedlings.

A commercial seed production system for Louisiana native coastal plant species smooth cordgrass (Spartina alterniflora) can be used to fulfill seed demand for a large-scale planting and revegetation. To develop seed production field, smooth cordgrass seed can be drilled-seeded in rows and managed under flooded conditions. Herbicide applications will be needed to control weeds, but there is no information available on the seedling tolerance to herbicides. To establish suitable herbicide applications and develop strategies to control weeds, 14 herbicides, fenoxaprop-p-ethyl, triclopyr, thiobencarb, penoxsulam, Imazosulfuron, halosulfuron-methyl, carfentrazone-ethyl, bensulfuron, pendimethalin, orthosulfamuron, imazethapyr, glyposate, quinclorac, and propanil (3',4'-dichloropropionanilide) were evaluated for their effects on the seedling survival and growth of smooth cordgrass. Herbicide spray was carried out at the three-to five leaf stage using rates of 0, recommended rate (1X), and two times of the recommended rates (2X) in a replicated completely randomized design. Smooth cordgrass seedlings showed very good tolerance to penoxsulam, quinclorac, orthosulfamuron, bensulfuron, and pendimethalin. At 2X application rates, these herbicides caused no visible injury with 100% seedling survival rate. Herbicide imazosulfuron, halosulfuron-methyl, and carfentrazone-ethyl produced minimal injury (5%) with more than 95% seedling survival rate. Thiobencarb, caused 40% seedling mortality and reduced the plant growth by 30%. Very severe plant damage was resulted from the application of fenoxaprop-p-ethyl, propanil (3',4'-dichloropropionanilide), imazethapyr, glyposate, and triclopyr.