July 15, 2011

Over the past few years there have been some changes regarding roadside vegetation management with a shift focused on three things: (1) reducing maintenance costs, (2) implementing native vegetation on the right-of-way and (3) selectively removing problematic, undesirable weeds and invasive species.


Over the past few years there have been some changes regarding roadside vegetation management with a shift focused on three things: (1) reducing maintenance costs, (2) implementing native vegetation on the right-of-way and (3) selectively removing problematic, undesirable weeds and invasive species.

Several herbicide products have been recently developed and are now on the market, showing good promise at aiding the three focus areas mentioned above. The purpose of this article is to highlight some of the research that is currently being conducted by the Habitat Lab in the Department of Forestry and Natural Resources of Purdue University.

Finding a fit

A good portion of what our lab researches is how several of the newly developed herbicides fit into the vegetation-management industry. Through numerous university and manufacturer tests, the products that we test are proving to curb the tide of resistance and improve control of difficult species that are so common on roadside rights-of-way (ROWs). With the recent development of these herbicides, roadside vegetation can, in our opinion, be reviewed and adjusted to move away from the status quo (mowing) to the use of environmentally friendly, cost-effective, tolerance/resistance curbing methods for safer, cleaner and more efficiently maintained roadsides. Please keep in mind that tank mixes will act differently on different species groups that are present in your respective location; however, the various tank mixes that we have been researching are showing to be an effective means to control broadleaf weeds as compared with mowing alone.

Native warm-season grasses and forb species also are being considered in an effort to reduce the cost of maintenance in certain areas. There are many other benefits to the ROW, in addition to reduced maintenance costs, which are described in greater detail later in the article.

Integrated intention

With funding from several entities, we are currently developing an integrated vegetation management (IVM) plan for Indiana roadsides. As a result of conducting this research, we have had the opportunity to host field days and training events, which we utilize to inform and train stakeholders from across the country of the various aspects of an IVM plan.

An integrated plan brings multiple management tools together and makes them work more effectively for the land manager. A simple example of this would be the implementation of plant growth regulators (PGRs) combined with broadleaf selective herbicides. This combination of treatments will reduce the number of required mowing cycles by reducing grass growth through seed-head suppression and killing the broadleaf weeds that can cause line-of-sight obstructions.

Mowing may still be necessary later in the year, once the effects of the PGRs have become reduced and due to some grasses’ ability to tolerate the effects of the PGRs. Furthermore, understanding the ecology/biology of the vegetation to be managed can allow for more successful management through proper timing of applications and mowing cycles.

Our IVM project is composed of two parts: (1) use of herbicide to control vegetation; and (2) selection of native alternative vegetative cover. Research discovery will allow INDOT and other states’ DOTs to implement best management practices for roadsides, resulting in greater native species biodiversity, greater control of invasive species and reduced maintenance costs.

Plotting answers

The vegetation-management aspect includes multiple control techniques including PGRs, selective broadleaf products, a combination of PGR and selective broadleaf control products, and mowing. Research sites in 2010 were located in three management districts representing three regions of Indiana (north, central and south) in an effort to compare regional differences among treatments and management practices. In the early spring of 2011, six additional sites were selected to allow for a thorough assessment of management needs by region throughout the state.

Treatments were applied in the spring and early summer, utilizing a research sprayer that was specially designed to mimic the equipment being utilized by INDOT for herbicide applications. The sprayer has the capability to hold six tank mixes with individually plumbed lines allowing for complete tank mix isolation. An additional tank holds clean water, allowing for all hoses, pumps and nozzles to be flushed, further reducing the potential of cross-contamination of treatments.

The sprayer is mounted in a trailer and towed by a truck, which is outfitted with ground speed radar and a Raven 440 monitoring system allowing for treatments to be applied at a rate of 30 gal per acre by keeping a constant speed of 13 mph. Plots are one-half mile each in length and extend 18 ft from the shoulder of the road and are randomly replicated three times to allow for statistical rigor. Vegetation inventories are taken on a regiment of 14, 30, 45, 60, 90, 120 and 365 days after treatment, rating vegetation response to treatments, estimates of overall effect to individual species and the vegetative complex as a whole.

In addition to these large-scale test plots, we are regularly testing products on target species in small plots. A CO2 pressurized backpack sprayer is outfitted with a set of nozzles to mimic broadcast applications at constant rates ranging from 20 gal per acre to as much as 50 gal per acre to mimic hand-gun applications.

Often we target invasive plant species; in other studies we simply focus on a particular problematic species of the industry. Much like our larger roadside plots, a stringent data-collection regimen is in place to capture treatment effects through time. Utilizing side-by-side plots, which range in size from individual stems (brush and tree species) to 10-ft by 20-ft areas (herbaceous broadcast applications), allows for visual comparison of treatments. These small plots are regularly used to demonstrate treatment differences to stakeholders during our field days, both visually and through data summaries and photographs taken at different points throughout the season.

The alternate vegetative cover portion of our research consists of the selection of native warm-season grasses and forbs to be planted along roadsides and other ROWs. For the 2011 growing season, six sites were selected across the state of Indiana and are currently undergoing the planting process. These sites are locations that have historically held a maintenance regime of mowing several times per year, such as cloverleaves and broad ROW. These sites were selected in order to target those areas that could receive less maintenance on a yearly basis and shift toward a two- or three-year maintenance schedule.

There are several reasons for using native grass and forb species in the ROW. Low-maintenance plant community, resilience to invasion of invasive species, pollinator corridors, increased biodiversity and an additive source of native vegetation seed and genetic inflow for existing natives are some good examples of what native vegetation brings to the ROW. Furthermore, if proper species selection and planting rates are utilized, then native vegetation has the potential to outperform non-native species in terms of longevity and survivability due to morphological and geographical traits.

Native vegetation requires less maintenance than traditional roadside vegetation cover due to the adaptations of the native species. Properly selected and planted community types will tolerate the conditions and climate of a particular region better than non-native species as adaptations to regional water stress, heat and other growing conditions are naturally present in native species. Growth characteristics and species relationships keep each other in check and make a more uniform composition, which will minimize maintenance requirements as found in other systems.

As a result of the community structure and species relationships, invasibility by other species that are not part of the native assemblage is impeded (but not totally removed) by competition and reduced available resources. Due to minimized rates of invasion, maintenance needs are further reduced, but not altogether removed. There remains a need for periodic maintenance in native vegetation communities, as many invasive species are strong competitors for those remaining resources and/or are superior competitors; invasives will therefore fill a niche not currently occupied by the planted native vegetation.

Biodiversity is a large component of the use of native grasses and forbs in the ROW. With the richness of species found in native warm-season grass communities, a multitude of species benefit from its health. The insects that eat and pollinate the flowers and grasses in these plant communities become food sources for birds and rodents specific to these habitats. Albeit, this habitat is small in expanse, but it can still act as an excellent corridor for these species to travel to and from breeding grounds and other habitat that is more suitable for permanent residence. Today’s fragmented landscapes need as much connectivity as possible to minimize the detrimental effects that can arise from the loss of habitat and connectivity between habitats.

Seeking a right way

Realizing that not every acre of the ROW will be planted in native warm-season grasses and forbs is key to the effort of producing cost-effective and management-compatible seed mixes, planting rates and planting locations. Efforts need to be focused on putting the proper seed mix for the acre to be planted to maximize the effectiveness of natives on the ROW. The need for alternative species mixes to suit the variety of soils, management strategies and public perception has been gaining attention for several years. As a result, prior research and experiences are being put into practice on Indiana roadsides to determine the best seed mixes for future plantings.

There is an increasing need for ways to cut costs associated with vegetation management, yet the need for safe and properly managed ROW is only growing with our expanding population. There are numerous areas of vegetation management, specific to ROW, which are in need of further research. The next time you are driving down the road and come across an area that looks a bit untidy with pin flags and “Do Not Mow or Spray” signs scattered about, remember this: Vegetation management isn’t easy, and it takes a lot of research and test runs before an appropriate IVM plan can be implemented. For more detailed information, test results and photos, please check out our website at: web.ics.purdue?.edu/~mkrausha.

About The Author: Kraushar is a habitat specialist and graduate research assistant, wildlife science, for Purdue University’s Forestry and Natural Resources.

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