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17.  EFFECTS OF LEAFY SPURGE (EUPHORBIA ESULA L.) CONTROL ON THE WESTERN PRAIRIE FRINGED ORCHID (PLATANTHERA PRAECLARA SHEVIAK AND BOWLES)

Ann M. Erickson* and Rodney G. Lym1

Abstract: Habitat invasion by leafy spurge is a threat to the survival of the western prairie fringed orchid (WPFO). Leafy spurge is very difficult to control with methods other than herbicides, but by law, herbicides cannot be used in habitats that support the orchid. Long-term control of leafy spurge without harming the WPFO may be achieved with the use of flea beetles (Aphthona spp.) as biological control agents. However, establishment of the flea beetles has not yet been successful within the habitat of the WPFO. Initial research found imazapic and quinclorac provided good leafy spurge control with little or no injury to the orchid. The purpose of this research was to control leafy spurge using both herbicides and biological control agents in an area that supports the WPFO. Treatments include insects alone, insects plus herbicides, and herbicides alone. Each herbicide was applied in the fall of 2000 at two application rates to 1 m2 containing a single orchid in the Sheyenne National Grassland. During the summers of 2001 and 2002, the effect of treatment on orchid recruitment and flower and seed production will be determined. Flea beetle populations will be estimated by determining the number of adults that emerge from soil cores and by evaluating adult population in the field. Leafy spurge control will be monitored by sampling density of leafy spurge stems both before and after treatment. The long-term goal is to maintain leafy spurge below densities that interfere with the WPFO.
 


1Ann M. Erickson and Rodney G. Lym, Graduate Research Assistant and Professor, Department of Plant Sciences, North Dakota State University, Fargo, ND 58105. *Presenter.

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