A test of two herbicides for use on banana poka (Passiflora mollissima (Kunth) L.H. Bailey) in Hawaii Volcanoes National Park

Abstract

Banana poka (Passiflora mollissima (Kunth) L.H. Bailey), an ornamental vine introduced to Hawai'i from South America, has become a serious pest in rain forests of three of the Hawaiian Islands. In Hawaii Volcanoes National Park, banana poka has invaded much of 'Ola'a Tract, where it damages native trees and displaces forest understory plants. Two herbicides in three different concentrations were tested for use against banana poka in '0la'a Tract. Treatments were Garlon 3A (triclopyr) and Roundup (glyphosate), each undiluted and at 50% and 5% dilutions in water. Herbicides were applied to the cut surfaces of banana poka stems near the point of rooting. Water applied to cut-stem bases served as a control and a test of the effectiveness of cutting alone. Sample size for each treatment was 10 vines. All treatments, including the control, killed 100% of banana poka stumps. However, the aerial portions of the vines survived and rooted in 40% of the water control plants and 10% of vines treated with 5% Garlon 3A. In the other five treatments, all vines were killed. Ten common, widespread native plant species and many others of sporadic occurrence were monitored in plots surrounding treated banana poka. Three woody plant species, four ferns, and two herbs generally remained constant or increased in numbers over the year in plots of most treatments. Only one fern species (ho'io-kula or Pneumalopteris sandwicensis) showed a significant decline in numbers; this occurred in the undiluted Garlon 3A treatment. Several other native tree and shrub species of more limited occurrence showed losses over the year in the undiluted Garlon 3A, undiluted Roundup, and 50% Roundup treatments. The 5% dilution of Roundup is recommended as an effective cut-stump treatment for banana poka, with no observed negative impacts on surrounding native vegetation.