Issue Feature

Glyphosate Helps Establish Native Wildflowers

RoadWorks

From the August 2007 issue of Better Roads Magazine

by Jeffrey Norcini, Anne Frances, Sandra Wilson, Keona Muller, Deborah Miller, Doria Gordon, and Carrie Reinhardt-Adams

Establishing and maintaining roadside wildflower plantings has increased in the past 10 to 20 years. This includes an ever-increasing focus on native species and sustainable practices.

For example, in Iowa, burning is routinely used to manage remnant populations of native wildflowers and grasses. And when native wildflowers or grasses are planted, seeds often are derived from plants adapted to the local environment.  The reasoning behind this approach to seed sources — which is being used in other states as well — is the concept that plants will adapt better to their home site or region than that same species derived from a different environment, especially in noncultivated sites like roadsides. This ecotype concept was put forth early by the Swedish botanist Göte Turesson.

Although the cost of ecotype-specific seeds is relatively high, such costs can be offset by reduction in long-term maintenance and reseeding expense when plantings are managed properly.

Regardless of whether a plant is native, naturally occurring populations, which have existed for centuries or many decades in a particular area or region, likely have become locally adapted to that area’s environment. Plants that grow better in the site produce more offspring, which establish and produce offspring of their own.

A lot of debate exists about defining the degree of localness with regard to distance between the source population and the area where those plants or seeds are to be planted. Defining localness is not simply a matter of distance or political borders. Climate, habitat, soil, and elevation seem to be the most important issues in many cases. For example, a South Georgia ecotype of a particular native wildflower or grass is probably better suited for use in a bordering county in Florida than is an ecotype derived from the Miami area.

Ecotype-specific seeds are expensive because of their specialized nature and relatively limited areas where they can be used effectively. Often, ecotypes have been subjected to a certification process to provide the end user with verification about the seed origin.

Several obstacles hinder expanded use of native wildflower ecotypes, one of which is protocols needed to establish and maintain such plantings. Current methods used by roadside vegetation managers to establish wildflower plantings need to be evaluated to determine whether they are appropriate for plantings established with the relatively expensive ecotype-specific seed.

The Florida Department of Transportation made a strong commitment to the planting and preservation of native ecotypes of wildflowers using methods that will maximize the economic, ecological, and aesthetic benefits from the state’s investment in the roadside wildflower program, as well as improve roadside safety.

Ecotype-specific protocols enhance roadside aesthetics and reduce mowing costs, as well as enhance roadside safety, since there would be less need for maintenance personnel and their equipment. However, FDOT guidelines on establishing and maintaining wildflower plantings are based on the use of wildflower seed that are either not native or are purchased from out-of-state suppliers. These guidelines were formulated on the best information that FDOT could compile, but most were not based on scientific evaluation of establishment and maintenance methods under Florida’s growing conditions. Current methods used by the Florida DOT to prepare sites for seeding of wildflowers range from no preparation (drill seeding into dormant turf) to application of glyphosate and subsequent tillage to reduce competition from turf.

As part of a field study of factors affecting roadside establishment of Florida ecotypes of native wildflowers, we evaluated use of glyphosate in no-till, simulated roadside sites in northwestern (Quincy, Gadsden County), northern central (Citra, Alachua County), and southeastern (Fort Pierce, St. Lucie County) Florida, where bahiagrass cover was moderate to moderately dense.  Bahiagrass is a very competitive and drought-tolerant turfgrass commonly planted along Florida’s roadsides for erosion control; however, due to its competitive nature bahiagrass can hinder wildflower establishment.

Two years ago, two applications of glyphosate were applied 10 to 14 days apart to replicated 10- by 13-foot plots, with the second application 10 to 14 days prior to seeding. Nonsprayed plots served as controls. Just before seeding, sprayed and nonsprayed plots were mowed to 1 to 2 inches; nonsprayed plots will be referred to as mow-only plots. Seeds of Florida ecotypes of native wildflowers were obtained from commercial producers in Florida. Species sown, which varied by site, were blanketflower, lanceleaf tickseed, Leavenworth’s tickseed, and standing cypress.

In August of last year, wildflower establishment was greater in plots treated with glyphosate compared to mow-only plots based on visual estimates of percent coverage. At Quincy, percent cover of blanketflower, lanceleaf tickseed, and Leavenworth’s tickseed was 16, five, and 13 times greater, respectively, in glyphosate-treated plots compared to mow-only plots. Similarly, at Citra, percent coverage in the glyphosate-treated plots of blanketflower, lanceleaf tickseed, Leavenworth’s tickseed, and standing cypress was 23, four, 13, and 11 times greater, respectively, in glyphosate-treated plots.

Results were less dramatic at Fort Pierce, where percent coverage of Leavenworth’s tickseed was only two times greater in glyphosate-treated plots compared to mow-only plots. The Fort Pierce results were at least partly attributed to the relatively high establishment rates in both glyphosate-treated and mow-only plots.

Regardless of site, the greater percent of wildflower coverage in glyphosate-treated plots appeared to result from glyphosate suppression of bahiagrass.  These results indicate that glyphosate may improve the initial establishment of wildflowers, but it is not yet clear if the established wildflowers will become self-sustaining populations.

University of Florida/IFAS
North Florida Research & Education Center
http://nfrec.ifas.ufl.edu/norcini

 

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