Short-term disruption of a leafy spurge (Euphorbia esula) biocontrol program following herbicide application

Abstract

Integrated pest management (IPM) for invasive plant species is being advocated by researchers and implemented by land managers, but few studies have evaluated the success of IPM programs in natural areas. We assessed the relative effects of components of an IPM program for leafy spurge (Euphorbia esula), an invasive plant, at Theodore Roosevelt National Park, North Dakota. Effects of herbicides on leafy spurge abundance and on dynamics of flea beetles (Aphthona spp.) used to control leafy spurge were evaluated over three field seasons following herbicide application. We monitored leafy spurge-infested plots with established flea beetle populations that had received picloram plus 2,4-D in September 1997 or 1998, imazapic in September 1998, versus those with no chemical treatment. Mature stem counts did not differ significantly between treated and untreated plots in 2001, suggesting that leafy spurge stands had recovered from herbicide treatment. Flea beetles were less abundant on plots with a history of herbicide treatment. Structural equation models indicated that in 2000 negative correlations between relative abundances of the two flea beetle species were greater on plots that had received herbicide treatments than on those that had not, but by 2001 no differences were apparent between treated and untreated plots. These results suggest that the most effective component of IPM for leafy spurge at this site is biological control. All herbicide effects we observed were short-lived, but the increased negative correlation between flea beetle relative abundances during 2000 implies that herbicide application may have temporarily disrupted an effective biological control program at this site.

Integration of biological control into weed management strategies.

“…In leafy spurge (Euphorbia esula L.) stands treated in autumn with 2,4-D and picloram, Aphthona spp. were shown to be temporarily less abundant compared to untreated plots, with no significant long-term benefit to weed control (Larson et al, 2007). The authors felt that the flea beetles may have abandoned the herbicide-treated patches for greater resources available in untreated plots.…”

Leafy Spurge (Euphorbia esula) Affects Vegetation More Than Seed Banks in Mixed-Grass Prairies of the Northern Great Plains

“…Herbicides have been used for leafy spurge control in TRNP since 1960, but use escalated in the mid-1990s, with up to 210 ha yr 21 being treated with over a dozen formulations (Larson et al 2007). Multiple herbicide treatments were used in the Knutson Creek drainage from 1985 to 1998 (Samuel and Lym 2008), but the specific locations of these treatments are unavailable.…”

“…Biocontrol organisms were first released at TRNP in 1987, but large releases started in 1992 (Andrascik 1994), with more than 18 million biocontrol flea beetles released between 1989 and 2004 (Prosser 2004). These control efforts eventually reduced cover of leafy spurge in the park (Larson and Grace 2004;Larson et al 2007) to the point that only a few scattered patches were identifiable via hyperspectral remote sensing in 2002 (Anderson et al 2004). We identified all biocontrol release locations (Hager 1998) within 200 m of our plots, a distance that flea beetles can travel in 2 wk (Jonsen et al 2001), using geographic information system (GIS) software (Quantum GIS v. 1.8.0) ( Table 1).…”