Pre-and postemergence herbicide tolerance of tropical fimbry, a native Hawaiian sedge with potential use for roadside revegetation

Abstract

Tropical fimbry (Fimbristylis cymosa) is a salt, wind, and drought tolerant sedge under consideration as a native roadside revegetation species in Hawaii. Multiple rate studies were conducted on transplanted tropical fimbry plugs to identify pre- and postemergence herbicides that are safe for selective weed control during plant establishment. The response of newly transplanted tropical fimbry plugs to applications [1 and 44 days after transplanting (DAT)] of oxadiazon (2.0 and 4.0 lb/acre), oryzalin (2.0 and 4.0 lb/acre), and oxadiazon + oryzalin (2.0 + 2.0 and 4.0 + 4.0 lb/acre) were evaluated at 212 DAT through visual vigor ratings and seedhead counts. Response of established transplants to the postemergence broadleaf herbicides, aminopyralid (0.06 and 0.11 lb/acre) sulfosulfuron (0.06 lb/ acre), prepackaged mixes of carfentrazone-ethyl + (4-chloro-2-methylphenoxy)- acetic acid (MCPA) + mecoprop + dicamba (0.02 + 1.11 + 0.22 + 0.11 lb/acre), and carfentrazone-ethyl + 2,4-D + mecoprop + dicamba (0.02 + 0.77 + 0.24 + 0.07 lb/ acre) were evaluated through visual vigor ratings 35 days after spraying (DAS). Results of the preemergence study indicate that low rates of oxadiazon and oryzalin provided an acceptable level of growth suppression to the sedge (>60% visual vigor). Postemergence applications of the prepackaged formulations of carfentrazone-ethyl resulted in moderate to high foliar injury (46% to 74%) and plant mortality (17% to 23%). Plants treated with sulfosulfuron showed signs of stunting (visual vigor of 36%), but exhibited the least foliar injury (16%) and no mortality. Plants treated with high and low recommended rates of aminopyralid exhibited very low injury ratings (1% to 2%) at 35 DAS. Results obtained from these preliminary studies identified oxadiazon, oryzalin, and aminopyralid as potentially safe for controlling weed species in transplanted tropical fimbry.