Chippewa Prairie in western Minnesota is a place where a person can sense the character of the once vast tallgrass prairie. Flanking the Lac qui Parle Reservoir on the Upper Minnesota River, this 2,866-acre remnant prairie provides critical habitat to migratory waterfowl, grassland birds, rare butterflies, and other wildlife. The natural area also serves as a vital link to Big Stone National Wildlife Refuge and Lac qui Parle Wildlife Management Area.
The Nature Conservancy (TNC) and Minnesota Department of Natural Resources (DNR) jointly own and manage Chippewa Prairie Preserve. In 2012, 240 acres of grassland were added to The Nature Conservancy preserve affording a higher level of protection for native plants and wildlife in the adjoining natural area, and increasing the preserve’s size by nearly 20 percent.
“The 240-acre addition was established as part of the Conservation Reserve Program,” explains Joe Blastick, Land Steward with The Nature Conservancy. Although grasses were well established there were few forbs, and Siberian elm (Ulmus pumila) infested most of the 240-acre parcel.
“Our goal is to improve the overall condition of this new parcel, but to accomplish this we knew we had to first remove the elm,” Blastick says. In 2012, TNC partnered with Dow AgroSciences LLC (DowDuPont) to develop and implement an integrated management strategy for Siberian elm, and measure plant community response following tree removal on the newly acquired parcel.
Siberian elm was introduced to the area in windbreak plantings and from windblown seed. The oldest trees were up to 24 inches in diameter and 50 feet tall, with elm seedlings invading the grassland within several hundred yards of mature trees. The infestation was too large for backpack herbicide treatments or hand removal so a combined strategy was developed that included prescribed fire, cutting followed by cut-surface herbicide treatments on large elm, and aerial herbicide application on smaller trees and seedlings.
Dow AgroSciences LLC provided Milestone® and Garlon® 4 Ultra herbicides for the aerial application, and TNC provided project oversight, physical removal and cut stump treatment of larger Siberian elm, and paid for the aerial application. Baseline plant community data including percent cover of grass, forbs (wildflowers), and woody vegetation were collected along six permanent transects by Paul Bockenstedt, Ecologist with Stantec Consulting Services Inc., the summer of 2013 prior to herbicide application. The mean percent vegetative cover before treatment was 59 percent (%) grass, 18% Siberian elm, 1% non-native forbs, and 12% native forbs. Goldenrods (Solidago sp.) comprised about 80% of the desirable forb component, the vast majority of which was Canada goldenrod (Solidago Canadensis).
Blastick explains that timing various management activities was critical to the success of the project. The 240-acre unit was burned in May 2013 to remove accumulated duff and litter, rejuvenate warm-season grasses, and stress Siberian elm trees. Small Siberian elm were allowed to grow and develop leaves during the summer before the fall herbicide treatment. Larger trees were cut, piled and a 25 percent solution (v/v) of Garlon® 4 Ultra and basal oil was applied as a cut-surface treatment in June 2013. Herbicides were broadcast applied aerially with a helicopter to smaller trees in September 2013.
Two different herbicide rates were used:
Area 1 (120 acres) received Garlon 4 Ultra at 5 quarts per acre (qt/A) plus Milestone® at 7 fluid ounces per acre (fl oz/A).
Area 2 (88 acres) was treated with Garlon 4 Ultra at 3 qt/A plus Milestone at 5 fl oz/A.
Area 3 (0.5 acre) was the non-treated control.
Managers realized that fire alone would not kill the elms, but they felt that a combination of stress from the fire and proven effectiveness of the herbicides should provide good control.
To ensure maximum uptake and translocation of herbicide in target trees Dow AgroSciences LLC recommends herbicide application to woody vegetation PRIOR to burning. Recommended application rate for controlling elm is Garlon® 4 Ultra at 4 qt/A plus Milestone® herbicide at 7 fl oz/A. A higher rate was used in this study because the site was burned prior to herbicide application. Dow AgroSciences field specialists are available for field visits to help with choosing the right herbicide and rate for brush control projects.
Woody Plant Control in Northern Prairies
Data collected by Bockenstedt nine months after herbicide application and one year post burn indicate that the combination of herbicide and fire provided 100% control of Siberian elm trees and seedlings within transects. Grass cover increased to a mean of 93% across the six transects in the higher rate treatment (Area 1). Visual observations taken in the lower treatment rate (Area 2) indicates similar control. The area will need to be monitored another year to determine if there is a difference in long term control between the two herbicide application rates. “Compared to treated areas, the non-treated control plot had a lot of seedling Siberian elm, Canada thistle and other weedy species,” explains Bockenstedt.
Joe Blastick with TNC agrees. “Siberian elm and Canada thistle control looks excellent, so we are very pleased with results. The aerial broadcast application was conducted on an old Conservation Reserve Program field that provided good wildlife habitat, but had a low diversity mix of Indian grass (Sorghastrum nutans), little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardi), and switchgrass (Panicum virgatum) along with undesirable grasses including Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis). This was an efficient way to make an application to reach our objectives of removing the Siberian elm,” says Blastick.
Blastick explains that their long term goal is to showcase the site for habitat improvement. “Getting rid of the large Siberian elm trees and encroaching seedlings was critical for opening up the landscape for grassland birds. We are hoping the herbicide application hit the ‘reset button’ and the combination of patch-burn grazing and haying will keep future tree encroachment at bay. We realize that some manual cutting of trees will have to be done in the future, but by integrating fire, rest, grazing and haying we hope to achieve structural heterogeneity across the site. We know that various wildlife species require different habitat so with this project in conjunction with the adjoining natural areas we are maximizing habitat for more species.”
The Chippewa Prairie Complex is soon to be listed as critical habitat for the Poweshiek skipperling (Oarisma poweshiek) and Dakota skipper (Hesperia dacotae), small butterflies most often found in undisturbed native prairie remnants. PHOTO BY PHIL DELPHEY, USFWS.
The mission of The Nature Conservancy is to conserve the lands and waters on which all life depends. Founded in 1951, The Nature Conservancy is the world’s leading conservation organization working in all 50 U.S. states and 35 different countries. Through the dedicated efforts of more than 600 scientists and over one million members, The Conservancy has protected more than 119 million acres of land and 5,000 miles of rivers, and operates more than 100 marine conservation projects globally. The Nature Conservancy is the largest environmental nonprofit both by assets and revenue in the Americas.
DRIFT CONTROL TECHNOLOGY
Scotts Helicopter Services in Le Sueur, Minnesota applied the aerial herbicide treatment. Equipment was selected to minimize off-site drift during application, and GPS mapping was used to precisely deposit the herbicide within the treatment area. Application equipment was a Bell 37-Soloy helicopter with a 100-gallon spray tank. The 30-foot spray boom was equipped with 28 Bishop Accu-Flo™ nozzles (1.4 gallon per minute output/nozzle) with a total pattern width of 48 feet. This lightweight nozzle produces a high percentage of large, uniform size droplets to reduce drift during application. Total application volume was 10 gallons per acre and the application time for the 240-acre project was about two hours.
Patch-burn grazing is a grassland management strategy designed to improve wildlife habitat by increasing grassland structure and diversity. With this grazing system, a portion of prairie is burned to attract grazing livestock. Animals concentrate their grazing in the burned “patch” even though they have access to the entire prairie. As new patches are burned, cattle shift their grazing to the most recent burned patch, allowing previously-burned areas to recover. Cattle have a strong grazing preference for grasses, as opposed to forbs (wildflowers), which further increases plant diversity in recently grazed portions of grasslands.
Published August 2014; reviewed and updated June, 2019.
®™Trademarks of Dow AgroSciences, DuPont or Pioneer and their affiliated companies or respective owners. Milestone herbicide is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. Consult the label before purchase or use for full details.
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