Leafy spurge (Euphorbia esula) Control and Soil Seedbank Composition Fifteen Years after Release of Aphthona Biological Control Agents

Abstract

Aphthona spp. flea beetles were released in two ecological sites of the Little Missouri National Grasslands in southwestern North Dakota in 1999 to control leafy spurge. The change in leafy spurge density and soil seedbank composition was monitored to evaluate the effectiveness of the biological weed control agent and the associated change in plant communities 5, 10, and 15 yr after release in loamy overflow (valleys) and loamy sites (ridges). In 2014, 15 yr after release, leafy spurge stem density had decreased 94% from 110 to 7 stems m−2 in the loamy overflow sites and 88% from 78 to 9 stems m−2 in the loamy sites. Leafy spurge represented only 2% and 6% of the loamy overflow and loamy seedbanks in 2004, respectively, compared with nearly 67% and 70%, respectively, in 1999. There was a slow shift to reintroduction of native species into the seedbank over the last 15 yr. The number of desirable species increased to 21 by 2014 (more than three times the number of species in 1999) in the loamy overflow sites, and doubled to 14 species in the loamy sites, while less desirable forb species doubled in both sites. Desirable grass species doubled in the loamy overflow sites by 2014 but remained unchanged in loamy sites. Aphthona spp. successfully controlled leafy spurge for more than 15 yr without any additional control methods or costs to land managers and resulted in the slow return of a subset of native species.