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12. SEEDBANK STUDY OF A LEAFY SPURGE INFESTATION.  John J. Sterling, Donald R. Kirby and Rodney G. Lym, Graduate Research Assistant and Professor, Department of Animal and Range Science, and Professor, Department of Plant Sciences, North Dakota State University, Fargo, ND 58105.

Abstract. Approximately 15 to 20% of the Sheyenne National Grassland in southeastern North Dakota is infested with leafy spurge (Euphorbia esula L.). The purpose of this research was to determine seedbank composition, which may play a role in future site revegetation during leafy spurge control efforts. Herbicide efficacy trial plots were established to determine herbicide rates to be used in controlling leafy spurge in areas that also contain the western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles). These plots were also used to determine seedbank composition. Three herbicides at two rates each were applied in the fall of 1997, glyphosate plus 2,4-D (0. 5 and 1 lb/A), AC 263,222 (0.0625 and 0.125 lb/A) plus Sunit (0.25 lb/A) plus 28% N (0.25 lb/A) and quinclorac (0.8 and 1 lb/A) plus Sunit (0.25 lb/A). Soil cores 2.5 cm deep were taken in May 1998 and were washed through a 4 min sieve and a 0.2 min sieve to remove coarse and fine materials. Samples were then spread 3 to 5 mm deep on a layer of sterile sand (approximately 1 cm), which prevented contact between sample and potting soil. Seed from a total of 56 composited (4 blocks, 7 herbicide treatments, 2 subsamples) soil cores were grown in the greenhouse. Seedlings were counted and removed after identification. Unidentified seedlings were transplanted until identification was possible. Removal of seedlings was necessary due to high seedling density. Identification continued until no further germination was noted approximately eight weeks after planting. Seedlings were identified by species and placed in categories of leafy spurge, forb, grass, grasslike and other species for statistical analyses. No statistical significance (p<0.05) was determined between the treatments using Tukey's mean separation test. Leafy spurge comprised 40% of all germinated seedlings, with grasses 25%, forbs 22%, grasslike 10% and other species 3%. Thirteen grass species were identified, four were desirable native warm season species [big bluestem (Andropogon gerardii Vitman), sideoats grama (Bouteloua curtipendula (Michx.) Torr.), little bluestem (Schizachyrium scoparium (Michx) Nash) and sand dropseed (Sporobolus cryptandrus (Torr.) Gray)] and three were desirable native cool season species [prairie junegrass (Koelaria pyramidata (Lam.) Beauv.), needle and thread (Stipa comata Trin. and Rupr.) and green needlegrass (Stipa viridula Trin.)]. Eighty-five percent of all grass seedlings that germinated were Poa spp. and would be considered undesirable at that level of presence. Twenty-eight forb species were identified of which 86% were considered undesirable (23 species) while 14% (5 species) were considered desirable natives [white prairie aster (Aster ericoides L.), wild strawberry (Fragaria virginiana Duchense), wood sorrel (Oxalis spp.), common evening primrose (Oenothera biennis L.) and black-eyed susan (Rudbeckia hirta L.)]. The competitive nature of leafy spurge and its high representation in the seedbank will present continuing control problems for revegetation efforts.

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