Native Forb and Shrub Tolerance to Milestone ® Herbicide Milestone ® (aminopyralid) is a broadleaf herbicide that has reduced risk to the environment compared with other commercially available herbicides, making it a desirable alternative for invasive weed control on rangeland and wildland sites. Effect of Milestone on desirable native forbs and shrubs is a consideration for land managers when making decisions about controlling invasive plants. Exp eriments were established at 16 locations in 6 states to determine long -term response of native forbs and shrubs to Milestone ® applied in summ er or fall, and to develop a tolerance/susceptibility ranking for native plants. Studies were established within diverse native plant communities in western Montana; Boulder and Steamboat , Colorado; Theodore Roosevelt National Park (TRNP), North Dakota; Glacial Ridge Preserve and restored prairies in M innesota; South Dakota Fish and Game, and o pen grassland near Grangeville, Idaho . This is a summary of multiple research locations completed by Mary Halstvedt, Dow AgroSciences Field Scientist . The follo wing researchers conducted the field experiments: Travis Almquist, Luke Samuel, Rodney Lym, North Dakota State University, Fargo; K. George Beck, Colorado State University, Ft. Collins; Roger Becker, University of Minnesota, St. Paul; Celestine Duncan, Weed Management Services, Helena, MT; Pat Green, US Forest Service Ecologist (Retired) ID; Michael Moechnig, South Dakota State University; and Peter Rice, University of Montana, Missoula. Materials and Methods: Plant communities with high levels of diversity were selected as research sites. Some locations had light to moderate infestations of invasive species such as Canada thistle , yellow starthistle, or spotted knapweed . Field experiments were designed as randomized complete block with two to five replications per treatment and initiated from 2004 to 2009. Herbicide treatments were Milestone ® at 5 or 7 fluid ounces/A . Broadcast ground applications were made with either a CO 2 backpack sprayer, or pickup boom sprayer. At one M ontana location a broadcast application was made with a helicopter. Treatments were made in late season (August/September/Oct ober) at seven locations, June /July at four locations, and June and September comparisons at two Minnesota and Colorado sites , and South Dakota. ® Trademark of Dow AgroSciences LLCLC Data collection across sites varied and included either canopy cover or plant counts along a permanent transect, or plant density within each plot. Table 1: Research Locations and Methods: Location Name Researcher Site Type Treatment Time Methods Code Rod Lym and Luke Milestone ® Pre and Post: 30 plots - 3 Theadore Roosevelt Western ND Canada thistle/arid October Samuel, North Dakota at 7 fluid frames/plot - 90 frames National Park USFS ND grassland 2004 State University oz/A per treatment Two Rivers and Post only: 20 frames per Milestone ® June and Hedquist- MN Dept of Southwest Roger Becker, Canada thistle prairie treatment for counts by at 5 fluid September Natural MN 2008 University of Minnesota restoration species and presence oz/A 2006 Resources(DNR) per plot Rod Lym and Travis Milestone ® Pre and Post: 90 frames Glacial Ridge Nature Northern MN Canada thistle prairie October Almquist, North Dakota at 7 fluid per treatment % cover by Conservancy GlacialRidge restoration 2006 SU oz/A species Open canopy, Larry Creek Bitterroot Western MT Peter Rice, University commercially thinned National Forest MTRice of Montana Ponderosa pine with Pre and Post: 5 reps - 4 spotted knapweed transects with 9 frames - Milestone ® Grant Cr. Elk Refuge Rough fescue October 180 frames per Western MT at 5 fluid National Wildlife Peter Rice grassland with spotted 2006 treatment. Canopy cover MTRice oz/A Federation knapweed and frequency of Open canopy, occurance Pattee Canyon Lolo Western MT Peter Rice Ponderosa pine habitat National Forest MTRice with spotted knapweed George Beck and Jim ® Pre and post data - Boulder, CO Diffuse knapweed Milestone Boulder Open Space Sebastian, Colorado June 2007 density of each species CO2007 upland rangeland at 5 fluid State University oz/A per plot. Celestine Duncan, ® Native rangeland with Helena, MT Native Rangeland Milestone Pre and post canopy Weed Management June 2007 good forb diversity MTDuncan weed free at 5 fluid cover by species Services oz/A Milestone ® Celestine Duncan and at 5 fluid Montana USFS Aerial Western MT Spotted knapweed October Pre and post canopy Andy Kulla, US Forest oz/A Operational Study USFSMT open canopy forest 2007 cover by species Service applied by helicopter Pre and Post: 5 reps - 4 Native bunchgrass and Milestone ® transects with 9 frames - Missoula, MT Peter Rice, University forb plant community Mount Sentinel at 7 fluid June 2008 180 frames per MTRice08 of Montana with moderate spotted oz/A treatment. Canopy cover knapweed infestation by species. Kufrin Waterfowl Plant counts taken per Morris Wetland Production Area Milestone ® June and Ortonville, MN Roger Becker, square yard for each Management Distirct Canada thistle control at 5 fluid September MNKufrin University of Minnesota species and % visual US Fish and Wildlife in 2 year old prairie oz/A 2006 cover by species restoration Native rangeland in George Beck and Jim Milestone ® July and Pre and post data - Steamboat, High elevation (8200 Western Colorado - 2 Sebastian, Colorado at 7 fluid September density of each species CO2009 feet) native rangeland locations State University oz/A 2009 per plot. Pat Green, US Forest Milestone ® Pre and post canopy Open grassland in Grangeville Native rangeland with August Service Ecologist at 5 fluid cover by species - 4 North Central Idaho IDGreen yellow starthistle 2009 (Retired) oz/A transects with 9 frames Micheal Moechnig, Milestone ® July and South Dakota Fish Big Stone, SD % Visual canopy cover by South Dakota State Native Prairie at 7 fluid September and Game SD2009 species University oz/A 2009 ®Trademark of Dow AgroSciences LLC First year post-application vegetation sampling was conducted in June and July the summer after treatment at all locations. Second year sampling was completed at 14 study sites. Individual rankings of tolerance to Milestone ® were established for 90 native forb species and 19 shrubs. Many species will show transient symptoms the year of treatment and those observations were not quantified. Evaluations were the year following treatment and were based on individual species reduction in canopy cover or density compared to non -treated controls or baseline data . Table 2: Four categories were developed for ranking tolerance of forbs an d shrubs to Milestone ® herbicide: Code Category Symptoms Injury Level Minimal symptoms <15% injury - may have Tolerant <15% T slight cupping of leaves Symptoms include cupping/yellowing and can MT Moderately tolerant inhibit flowering, with recovery the first growing 15 to 50% stand reduction season after application Injury could be significant the first year and may Moderately susceptible 51 to 75% stand reduction MS reduce stand Severe injury the season of application and stand reduction the year after treatment with Susceptible >75% stand reduction S possible death of established plants. Some plants may regenerate from seed bank Copyright 2012 Dow AgroSciences LLC Of the 90 forb species categorized, 23, 14, 19, and 34 were ranked susceptible (S), moderately susceptible (MS) , moderately tolerant (MT), and tolerant (T) , respectively at one year after application. Many forbs recovered by the second year following Milestone ® application with only 1 9 of 90 native forbs ranked either MS or S (Figure 1). Sunflower, yarrow, and lobelia were very susceptible to Milestone ® while lupine, golden Alexander and wild bergamot were very tolerant. Figure 1: Results of 90 f orb species with both 1 and 2 YAT (year after treatment) data showing increase in species tolerance by the second year following treatment. There were 29 plant families represented, with the greatest number of species (35%) in the Asteraceae family. ® Trademark of Dow AgroSciences LLC. Table 3: Tolerance rankings of forb species to Milestone ® herbicide. Forbs are listed alphabetically by common name within plant family and rankings are shown for 1 and 2 years after treatment (YAT). See Table 1 and 2 for locations and category description. Appl Common Name Family Genus Species 1 YAT 2 YAT Time Location Golden Alexanders Apiaceae Zizia aurea TT Fall Glacial Ridge Golden Alexanders Apiaceae Zizia aurea TT Summer MNKufrin Hearl-leaved alexanders Apiaceae Zizia aptera T NA Both MN2008 Nine-leaf lomatium Apiaceae Lomatium triternatum MT T Fall MTRice Wyeth's biscuitroot Apiaceae Lomatium ambiguum TT Fall MTRice Spreading dogbane Apocynaceae Apocynum androsaemifolium TT Fall Glacial Ridge Common milkweed Asclepiadaceae Asclepias syriaca TT Fall Glacial Ridge Arrowleaf balsamroot Asteraceae Balsamorhiza sagittata MS MT Fall MTRice Arrowleaf balsamroot Asteraceae Balsamorhiza sagittata MS+ MT+ Summer MTRice08 Black-eyed Susan Asteraceae Rudbeckia hirta S NA Both MN2008 Blanket flower Asteraceae Gaillardia aristata MT T Both MT Rice/Glacial/MTRice08 Canada goldenrod Asteraceae Solidago canadensis MT+ NA Summer SD/MN Kufrin Canada goldenrod Asteraceae Solidago canadensis MS MS Fall Glacial Ridge,MNKufrin cudweed sage Asteraceae Artemesia ludoviciana TT Summer MTDuncan Cup plant Asteraceae Silphium perfoliatum MT NA Both MN2008 Daisy fleabane Asteraceae Erigeron strigosus MT NA Both MN2008 Gay