Developing an effective glyphosate application technique to control Bischofia javanica Blume, an invasive alien tree species in the Ogasawara Islands

Abstract

Bischofia javanica is a non-native tree species in Japan's Ogasawara Islands, where it threatens native tree species due to its rapid propagation and growth. An effective method is needed to limit the expansion of B. javanica populations and to conserve the natural forest ecosystem of the islands. For this purpose, we examined the effectiveness of a new application technique for the herbicide glyphosate on B. javanica. In this method, glyphosate solution is directly injected into holes drilled in the stem, and each hole is then plugged with a cork stopper to prevent loss of the solution, namely the drill-and-plug method. We also developed an allometric regression model linking stem diameter with total aboveground biomass (AGB) to estimate the necessary herbicide dosage. Our results suggest that between 0.1 and 0.5 g kg−1 (active ingredient per unit AGB) is required to control most B. javanica trees. Verification of the drill-and-plug method using the minimum dosage (0.1 g kg−1) showed that most of the herbicide-treated trees were killed. These results suggest that the drill-and-plug method can help control the B. javanica invasion of the Ogasawara Islands.