The Response of Weeds and Cut Stems of the Native Hawaiian Grass Sporobolus virginicus (L.) Kunth to Two Forms and Two Rates of Oxadiazon Applied As a Component of a Hydromulch Cap In a Simulated Roadside Planting

United States Department of Transportation initiatives are calling for increased use of native plants for highway rights-of-way re-vegetation.  In Hawaii, Sporobolus virginicus (a coastal native grass) has been identified as a useful species for roadside plantings.  Plantings of S. virginicus can be accomplished by hydromulch capping of cut stems, however, weed management is essential for successful establishment.  In this study, the efficacy and safety of the pre-emergence herbicide oxadiazon applied in the hydromulch cap over S. virginicus cut stems was evaluated in a trials repeated over two years.  Oxadiazon in two forms, granule and suspension concentrate, was applied at 2.25 and 3.36 kg ai ha^-1.  S. virginicus response was recorded as counts of new shoots, aboveground biomass and percent visual coverage.  There were significantly greater counts of S. virginicus shoots, biomass and visual coverage found with the G form of oxadiazon, with no significant effect of application rate.  Herbicide treatments with the G form of oxadiazon resulted in significantly less weed biomass than the suspension concentrate, with no significant effect of rate.  Granular oxadiazon, in the hydromulch cap, can provide commercially acceptable weed control while maintaining high levels of rooting and plant vigor during the establishment period.

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