Most management tactics used against leafy spurge are not economical, practical, or efficacious when used alone. Combinations of the biological control agent, Aphthona beetles, the herbicide imazapic (105 g/ha), and interseeded native grass species were evaluated for leafy spurge management at two sites: Sheyenne National Grassland and Ekre Grassland Preserve in North Dakota during 2001 to 2005. At the Sheyenne site, over a 5-yr study period, leafy spurge was reestablishing its stem density after a single application of imazapic, but stand suppression was maintained to < 11 stems/m2 when management combined imazapic with Aphthona or interseeding of native grasses. Aphthona beetles established at the Sheyenne site, but declined as leafy spurge density decreased. However, the remaining Aphthona population continued to suppress leafy spurge density. Leafy spurge stem control was successfully maintained for 3 yr by Aphthona and grass competition without repetition of the imazapic treatment. Leafy spurge root dry weights were reduced by 66% (< 111g/m2) in the insect plots during this period. At the Ekre site, similar results were observed for the first 3 yr. However, in the fourth yr, a failure of biological control agents to establish resulted in the resurgence of leafy spurge. During this study, lower Aphthona emergence was observed in imazapic-treated plots, possibly due to reduced leafy spurge density.
Nomenclature: Imazapic; leafy spurge, Euphorbia esula L. (Euphorbiaceae); flea beetles, Aphthona spp. (Coleoptera : Chrysomelidae)