Anderson, R. C., and D. E. Gardner. 1999. Biological control of kahili ginger in Hawaiian forests. Abstracts of the X International Symposium on Biological Control of Weeds; 4-14 July, 1999; Bozeman, Montana. P. 63.
ABSTRACT
Ralstonia solanacearum was tested for its efficacy as a bioherbicide for the alien kahili ginger (Hedychium gardnerianum) in Hawaiian forests. This weed was inoculated with an aqueous suspension (1 x 106cells/ml) of the ginger infecting strain of the bacterium, combined with an organosilicone surfactant, in 10 x 10m2plots in heavily invaded Metrosideros wet forests of Hawai'i Volcanoes National Park. Treatments consisted of spraying mechanically wounded and non-wounded rhizome mounds and shoots in both winter and summer. Controls were wounded only. In addition, half of the wounding treatments received a second application of the potential bioherbicide on regrowth after 6-8 weeks. No infections were observed in non-wounding treatments. In the wounding treatments, both rhizome and stem infections were observed in both the surfactant and non-surfactant based inoculum within 6-8 weeks. Shoot symptoms included interveinal chlorosis, water soaking, and epinasty. Rhizome symptoms included water soaking and decay of infected tissues. Seedlings germinating in treatment plots were also affected by the bacterium, causing death and stunting. Following inoculation, the number of stems produced on rhizome mounds varied within treatments. Some of the mounds had no regrowth, while others sprouted similarly to the non-treated controls. Many surviving shoots were much reduced in height and failed to mature or flower. Average infection rates of emerging shoots following the second application with and without surfactant were 35% and 25% respectively. Although treatment responses were inconsistent, preliminary results suggest that effective control of kahili ginger can be accomplished using R. solancearum as a bioherbicide with limited wounding assistance to enhance the spread of the bacterium and build up inoculum levels in the soil. The use of R. solancearum as a bioherbicide is a possible alternative to existing control strategies that are not practical on a large scale. However, application in areas where water runoff could occur to commercial edible ginger (Zingiber officinale) plantings should be avoided.
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