Fountain grass control in Hawai'i Volcanoes National Park 1985-1992

Abstract

Fountain grass (Pennisetum setaceum) is a perennial alien bunchgrass disruptive to native ecosystems in Hawai'i. Control of fountain grass began in Hawai'i Volcanoes National Park in the 1960's. Until 1985 the control program emphasized the core of the 8000 ha infestation in the park. Since 1985, fountain grass management has employed a two-step strategy, first controlling outlying populations and then the center of the infestation where fountain grass densities are higher. This report summarizes fountain grass population levels and workloads, 1985-1992, and thus addresses the effectiveness of a control strategy starting with satellite populations. There was a striking decline in number of fountain grass plants in satellite populations after 3-7 years of removing plants. Also, there appears to be little establishment of new populations in areas on the periphery of the main infestation and beyond. Workloads required to accomplish control of outliers decrease after intensive initial efforts. These trends indicate that the spread of fountain grass has been successfully checked, and that control efforts have been successful on the edge of the range. They also confirm the hypothesis of Moody and Mack (1988) that control is most successful when it focuses on satellite populations. Control of satellite populations should be maintained because of the capacity of fountain grass seeds to remain viable in the soil for at least 7 years. Management should also now emphasize the core of the infestation and employ the same intensive, systematic approach used with initial control of outliers. Successful control in this area cannot be predicted at this time because fountain grass densities have increased with suspension of management in 1985. However, the use of a pre-emergent herbicide promises to reduce workloads.