Introduction

Introduction thompsbb
A vehicle travels on a road alongside colorful roadside vegetation.

 

What is IRVM?

Integrated Roadside Vegetation Management is an approach to right-of-way maintenance that combines an array of management techniques with sound ecological principles to establish and maintain safe, healthy, and functional roadsides. The IRVM toolbox includes judicious use of herbicides, spot mowing, prescribed burning, mechanical tree and brush removal, and the prevention and treatment of disturbances such as farm field runoff and herbicide overspray to existing vegetation. IRVM’s long-term objective is to reduce roadside maintenance by creating stands of durable, long-lived native plants.

History

History thompsbb

IRVM techniques were introduced to Iowa in the mid-1980s in response to the need for groundwater and surface water protection. Prior to that time roadside weed control had relied exclusively on herbicides, with most counties employing an application method known as blanket spraying, also known as broadcast spraying, to spray wide swaths of the roadside. 

Besides being expensive and potentially harmful, blanket spraying was an ineffective means of weed control, creating openings for weeds by stressing and weakening roadside grasses and eliminating beneficial broadleaf species. Iowa counties were spending a lot of money putting large amounts of herbicide into the environment and, at the same time, making little or no headway in the control of roadside weeds. Clearly, this type of roadside management proved unsustainable.

Another development of the mid-1980s was the Iowa Department of Transportation’s use of native prairie grasses and wildflowers to control erosion and save money on fuel since native plants require less mowing than cool-season grasses. A few county conservation boards were also experimenting with this naturally adapted, alternative vegetation for roadsides. 

When the Iowa Legislature officially adopted IRVM in 1988, the cornerstone of the program became the establishment and protection of native vegetation in Iowa roadsides. The Living Roadway Trust Fund was created the following year, supporting state, city, and county roadside projects. For more information about the history of IRVM and the LRTF, see the 2018 report created by Jean Eells entitled “Iowa’s Living Roadway Trust Fund and Integrated Roadside Vegetation Management Program.”

Since that time over 100,000 acres of state and county road right-of-way have been planted to native vegetation. Diverse stands of 15–45 prairie grass and wildflower species—all naturally adapted to local growing conditions—provide stable, low-maintenance roadsides for Iowa.

IRVM Program

IRVM Program thompsbb

Goals

  • Maintain a safe and effective road system.
  • Provide responsible and sustainable vegetation management.
  • Make the most of Iowa’s immense 847,000-acre roadside resource. 

Basic Tenets 

  • Prevent soil erosion.
  • Control undesirable species in roadsides.
  • Do not rely exclusively on herbicides.
  • Plant the best-adapted vegetation.

The Road to Success for County Roadside Management

  • Create a full-time roadside manager position.
  • Hire a conservation-minded individual to run the program.
  • Give the roadside manager the power to succeed.

The Integrated Toolbox

  • Use the principle of species diversity for a strong, weed-resistant plant community. No single species is adapted to all roadside conditions. IRVM employs a mix of species suited to the range of growing conditions in a typical roadside and the varying climate conditions of an Iowa growing season. Any roadside planted to a monoculture will develop gaps for weeds to exploit.
  • Use herbicides sparingly. Overuse of herbicides weakens stands of grasses, allowing increased weed invasion. Careless use of herbicides also destroys beneficial broadleaf species that would otherwise help prevent weeds by occupying the same niche sought by broadleaf weeds.
  • Make more effective use of herbicides by spraying smarter with better training, better timing, and better technology.
  • Prevent disturbances. Farm field runoff and herbicide over-spray are common disturbances from adjacent land that destroy roadside vegetation and cause more weeds. Work with individual landowners to enlist their cooperation in reducing these negative impacts.
  • Conduct prescribed burns to promote healthy native vegetation. By burning native plantings every 3-5 years or so, trained and well-equipped crews use fire as the most effective means of managing fire-adapted prairie species.
  • Mow patches of weeds to reduce seed production and seed dispersal.
  • Use a variety of means to clear brush and trees before they block the vision of motorists, obscure signs, and become dangerous obstructions to errant vehicles.

The Benefits of Native Vegetation

Iowa road departments plant native vegetation for a variety of reasons:

  • Native plants are durable, long-lived perennials well-adapted to Iowa’s climate and growing season.
  • A diverse native planting adapts to a wide range of soil and moisture conditions.
  • Native plants perform well in poor soils.
  • Extensive native plant root systems provide superior erosion control.
  • Deep roots and dense above-ground foliage reduce stormwater runoff by intercepting raindrops, slowing water flow, and increasing infiltration.
  • Extensive roots and decaying foliage further increase stormwater infiltration by adding organic matter to the soil, making it spongier and more absorbent.
  • Root systems penetrate six to eight feet or deeper, enabling prairie plants to survive drought and high salt concentrations.
  • Extensive root systems deprive weed roots of water, nutrients, and space.
  • Tall prairie vegetation shades out Canada thistle and other weed seedlings.
  • A wide swath of prairie grass in the right-of-way traps blowing snow in some situations, increasing the storage capacity of the ditch and reducing the amount of snow deposited on the road.
  • Native roadside plantings provide valuable food and cover for songbirds, game birds, and small mammals.
  • Native roadside plantings provide important habitat for agricultural crop pollinators.
  • Native plants add color and natural beauty to the right-of-way.
  • Tallgrass prairie roadside plantings restore a piece of Iowa’s natural heritage.

Progress to Date

Herbicide use in Iowa roadsides has been reduced to spot-spray application and Iowa DOT and half of Iowa’s counties routinely plant native vegetation.

Since the early 1990s over 60,000 acres of state and 35,000 acres of county road right-of-way have been planted to native vegetation. Diverse stands of 20–45 prairie grass and wildflower species — all naturally adapted to local growing conditions — provide stable, low-maintenance roadsides for Iowa.

As of late 2023, 56 counties have an IRVM plan and 47 counties have a roadside vegetation manager. Counties with either a plan or a roadside vegetation manager collectively manage 308,000 acres of roadside vegetation using the principles of IRVM. 

As of late 2023, 19 cities have an IRVM plan. It is more difficult to estimate the number of city acres of right-of-way managed using IRVM techniques since unlike state and county highways, there is no comprehensive estimate of the amount of right-of-way in all Iowa cities.

The Challenge

Encouraging the remaining counties and cities to place more of a priority on roadside vegetation is a challenge. Many are not so much against IRVM as they simply are not inclined to do much of anything with their roadside vegetation.

Of Iowa’s land area of 35,860,480 acres (56,273 square miles; 2020 Federal Land Ownership Report), 4.3% is public land. Roadside rights-of-way comprise around 60% of this public land within Iowa (Figure 1), representing a significant area where sustainable management techniques can improve water quality, reduce soil erosion, enhance aesthetics, and provide other public benefits.

A graph showing total acres of the various types of public land in Iowa.

Figure 1. Public land use in Iowa (acres). Sources: Tara Van Waus, Iowa Department of Transportation; Iowa Department of Natural Resources, 2023; Iowa County Conservation System, 2016, 2023; Vincent et al., 2020.