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ISSUE 15   August 13, 1998



    Plateau has shown promise for leafy spurge control in North Dakota. However, grass injury especially to cool season species has been observed. The labeled rate for optimal leafy spurge control is Plateau at 8 oz product/A 2 weeks before a killing frost plus an additional 4 oz/A the following spring or at 12 oz/A in the fall. The label also states that Plateau should be applied with a methylated seed oil (MSO) adjuvant, such as Sun-It II or Scoil, and nitrogen fertilizer regardless of rate or timing. The objectives of this research were to evaluate Plateau applied with and without adjuvants and at differing times of treatment to maximize leafy spurge control with minimal grass injury.

    The first experiment evaluated Plateau applied in the mid-summer or fall for leafy spurge control at locations near Valley City and Jamestown, ND. Mid-summer treatments were applied to the flowering stage of leafy spurge and fall treatments during regrowth. Plateau applied mid-summer did not visibly control leafy spurge topgrowth 3 MAT. However, by the following spring [10 months after treatment (MAT)], Plateau at 16 oz/A alone or 8 oz/A plus a MSO averaged 90% control. Grass injury 10 months after the mid-summer treatment at Valley City averaged 28%, but was not visible at Jamestown. Plateau provided better leafy spurge control when applied in the fall than mid-summer. All fall- applied Plateau treatments averaged 99% leafy spurge control and 23% grass injury the following spring, 9 MAT. Plateau at 16 oz/A alone or 8 oz/A plus a MSO maintained 96% control 12 MAT with no grass injury compared to 37% control with Tordon plus 2,4-D.

    A second experiment evaluated Plateau applied at 2-week intervals from 15 August to 15 October for leafy spurge control at locations near Valley City, and Buffalo, ND. Plateau at 4 oz/A plus MSO reached a maximum of 90% leafy spurge control when applied in mid-September. Leafy spurge control with Plateau at 8 oz/A plus MSO averaged 90% when applied anytime during September, and was similar to control with Tordon plus 2,4-D. Leafy spurge control tended to be less when Plateau was applied before September 1 or after October 1. Grass injury was minimal, but tended to increase with the later Plateau application dates.

    The third experiment evaluated Plateau applied with or without adjuvants at locations near Walcott, Valley City, and McHenry, ND. Treatments were applied in early to mid- September to fall regrowth at all three locations. Plateau provided better leafy spurge control at 8 oz/A than 4 oz/A, and application with a MSO was necessary to provide long term control. Plateau at 4 or 8 oz/A plus MSO or plus MSO and 28% N averaged 95% leafy spurge control the following spring (9 MAT) at all three locations. The Walcott location was established one year earlier than the other two locations; all treatments were reapplied the following fall and evaluated 12 and 21 months after the first treatment (MAFT). Leafy spurge control was the best with Plateau at 8 oz/A plus MSO or plus MSO and 28% N, which averaged 66% control before the second treatment (12 MAFT) and 89% control after the second treatment (21 MAFT).

    In summary, Plateau provided better control when applied in the fall compared to mid-summer, especially when applied in mid-September. Plateau at 8 oz/A provided a broader application window for maximum leafy spurge control and provided longer lasting control compared to Plateau at 4 oz/A. Plateau plus MSO provided better leafy spurge control than Plateau alone or with 28% N adjuvant. In general, grass injury was minimal by 12 MAT regardless of treatment.

Denise M. Markle and Rodney G. Lym
NDSU Plant Sciences
Graduate Student and Professor



    The western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles) is a federally listed threatened plant species in the United States. Once widespread throughout the tallgrass prairie, its populations are now limited to isolated prairie remnants. According to the U.S. Fish and Wildlife Service there are approximately 40 populations of the western prairie fringed orchid remaining. The three largest known populations of the orchid occur in Minnesota and North Dakota in the United States and southern Manitoba in Canada, with one of the largest occurring in the Sheyenne National Grassland.

    Leafy spurge (Euphorbia esula L.) currently infests approximately 1 million acres of land in North Dakota including wide spread infestations on the Sheyenne National Grassland which located in Ransom and Richland counties of southeastern North Dakota. The grassland is a federally managed tract of remaining tallgrass prairie. Leafy spurge a noxious weed and therefore is required by law to be controlled or eradicated where infestations occur, including areas where threatened and endangered species occur. Leafy spurge infestations continue to expand on the sandy soils of the Sheyenne National Grassland having a negative impact on plant species diversity including the western prairie fringed orchid.

    Areas in the grassland that presently support the orchid are impacted by leafy spurge invasion. Management efforts are focusing on reducing leafy spurge without harming the orchid. Biocontrol methods have proven ineffective in controlling leafy spurge on the grassland. Aphthona spp. flea beetles have been introduced into the grassland many times but have yet to become established in populations large enough to control leafy spurge. The soil in the Sheyenne National Grassland can be over 90% sand and Aphthona spp. larvae have difficulty locating leafy spurge roots and rapidly desiccate.

    Preliminary research has shown that the western prairie fringed orchid will resume growth in areas where leafy spurge has been controlled by herbicides. The objectives of this research are to evaluate the effect of herbicides on the western prairie fringed orchid and leafy spurge growing in the same area. Three herbicides will be evaluated for their effectiveness in controlling leafy spurge and the effect on the recruitment of the western prairie fringed orchid. The herbicides to be evaluated include Landmaster BW, Paramount (quinclorac - a new BASF compound) + Scoil and Plateau + Sunit + 28% N. All herbicides will be applied in the fall of 1998 when the orchid is dormant. The long-term goal is to control leafy spurge without harming the orchid and restore the habitat of this endangered species.

John J. Sterling, Rodney G. Lym,
Donald R. Kirby & Carolyn Hull-Sieg
NDSU Plant Science Graduate Student & Professor
Animal and Range Science Professor, and Research Wildlife Biologist,
USDA Forest Service, Rocky Mountain Research Station



    A Section 18 has been issued for control of purple loosestrife with Garlon 3A in North Dakota. The Section 18 allows one ground application at a rate of 2 gallons/A (6 lb ai/A) and expires on September 30.

    Ostlund Chemical Co. in Fargo, among other distributors, has Garlon 3A product available. However, inventory is low. Should you wish to to contact them regarding product availability , telephone 1 800 729-8878 and speak to Tony Turner or Troy Schrader.

Rod Lym
NDSU Weed Science

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