Efforts to restore or rehabilitate mixed wildflower (forb)-grass prairie landscapes in the Midwestern United States are often compromised by the presence of invasive plants.
While herbicides provide effective control of invasive plants, they are often not used due to concern that herbicide residues may persist in the soil and impact establishment of wildflowers. Researchers in Wisconsin and South Dakota examined the response of common native wildflower species seeded in the fall or spring following treatments with Milestone® and Transline® herbicides. The results of this research provide promise for land managers balancing invasive plant control and restoring desirable prairie habitat.
Native tallgrass prairie historically included a mix of grasses such as big bluestem (Andropogon gerardii) and Indiangrass (Sorghastrum nutans), along with native wildflowers such yellow coneflower (Ratibida pinnata) and wild bergamot (Monarda fistulosa). These ecologically important prairies provide food and shelter for a wide variety of wildlife species. It is estimated that more than 99 percent of native tallgrass prairie has been destroyed or severely impaired in the Midwestern United States, highlighting the importance of efforts by public and private land managers to restore or rehabilitate mixed wildflower-grass prairie systems in this region.
Invasive plants such as Canada thistle (Cirsium arvense) can greatly impact the success of seeding both grasses and wildflowers. Although, best management practices recommend the application of herbicides to control noxious and invasive weeds prior to establishing mixed grass prairie systems, there is concern about the effect of herbicide residues on wildflower establishment.
In 2009, Dr. Mark Renz, University of Wisconsin and Dr. Mike Moechnig, South Dakota State University teamed up on a research project to determine the tolerance of common desirable prairie wildflowers to herbicide applications. Land managers identified this research as an important requirement for restoring native prairie due to the high cost of native wildflower seed and lack of information on the tolerance of wildflowers to herbicides applied prior to planting. The objective of the study was to determine if herbicides applied the summer prior to planting would reduce establishment of common wildflowers in mixed prairie plantings seeded in fall and the following spring.
The study sites were located at university research farms in Arlington, Wisconsin and Beresford, South Dakota. The site in South Dakota is located in the southeast part of the state within the Northern Tallgrass Prairie ecoregion, and the site in Wisconsin is in the Prairie-Forest Border ecoregion in the southcentral part of the state (Figure 1). The research sites were in either annual or perennial cropping systems prior to the study. Fields were chisel plowed then disked to prepare the seed bed (Wisconsin) or in a no-till system (South Dakota) prior to herbicide application. Experiments were established as a split-plot design with four replications of each treatment. Milestone and Transline herbicides were applied in July 2009 (mid-summer treatment). Glyphosate was applied to the study area to control annual weeds and dandelions prior to seeding. Wildflower species (Table 4) were planted with a no-till drill as a dormant fall planting in November four months after herbicide treatment (Table 1). With a dormant seeding, wildflowers are planted in the fall just before the soil freezes. The seed remains dormant in the soil until the following spring when they will germinate and grow as soon as conditions are favorable. The spring seeding date was in April, approximately nine months after herbicide treatment. Annual weedy grasses were controlled at both sites by applying grass-specific herbicides and mowing in 2010 in Wisconsin.
Researchers designed the study to evaluate if Milestone and Transline herbicide treatments influenced establishment of common prairie wildflowers planted in the fall as a dormant planting or the following spring. Density of planted species was measured 12, 18, and 24 months after application. Species within each site were analyzed separately by location by analysis of variance (p<0.05). Although various herbicides, rates, and combinations were applied in the experiment, results discussed below include the maximum broadcast use rate of Milestone® at 7 fluid ounces per acre (fl oz/A) and Transline® at 16 fl oz/A.
Results from the study showed that specific wildflower species varied in response to timing of planting and herbicide treatment (Table 2, Table 3, and Table 4), but rarely did both factors interact to change wildflower density.
Black-eyed Susan density was reduced by Transline® at 16 fl oz/A at Wisconsin but not in South Dakota when compared to the non-treated plots 24 months after treatment.
There was either no difference or an increase in wildflower density from herbicide treatments in 86% of the species seeded in the study compared to non-treated controls.
In Wisconsin, the spring planting date resulted in significantly more plants per meter row for blanket flower, black-eyed Susan, wild bergamot, lance leaved coreopsis, round headed bush clover and purple coneflower (p<0.05).
There was no interaction between planting date and herbicide treatment. Differences in wildflower establishment by planting date may be due to biotic factors such as seed depredation.
Results suggest that many native wildflowers can be seeded as a dormant fall planting or the following spring following a summer application of Milestone and Transline at rates evaluated (Table 4). These herbicides are also safe to grasses, providing additional management tools for improving the success of restoring mixed wildflower-grass prairies.
This article summarizes a paper presented at the 66th annual meeting of the North Central Weed Science Society (December 12-15, 2011; Milwaukee, WI) by Mark Renz, Mike Moechnig, and Mary Halstvedt. http://ncwss.org/proceed/NCWSS-2011-Proceedings.pdf
First Published 3/2013; Revised 6/2019
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