Successful right-of-way vegetation management methods challenge even the toughest unwanted species.
By Tara Beecham
Whether the land that needs protecting is as remote as a country roadside or as heavily trafficked as a national park, vegetation management is a necessary battle against invasive species. Without structured planning, motorist safety can be at risk, power lines can become damaged, and stormwater outlets can become clogged, causing flooding.
“Vegetation is one of those things that, if it’s left unattended for a few years, can grow out of control,” says Tucker Ferguson, acting director for the Bureau of Maintenance of operations for the Pennsylvania Department of Transportation (PennDOT), based in Harrisburg. “It needs to be maintained year after year.”
Mowing, brush cutting, herbicide use, and even biological programs that introduce insects or grazing animals are some right-of-way vegetation management approaches maintenance professionals employ across the United States. And it is a combination of two or more of these methods that has become increasingly prevalent.
Combining Methods for Roadside Safety
Integrated vegetation management (IVM) has become a staple at state transportation departments, including the Ohio Department of Transportation (Ohio DOT).
“IVM uses many different methods to control the vegetation in the most environmentally sound, cost-effective way possible,” says Scott Lucas, a transportation manager at the Columbus-based Ohio DOT, citing mowing, tree and brush trimming and removal, and herbicide applications as some of the practices the Ohio DOT uses. “Across the state, we use different control methods depending on what the desired outcome is and what vegetation needs to be controlled.We try our best to control the vegetation before it becomes a problem to the motoring public. This stays in line with our ‘safety first’ standard.We want to make sure the motorist can see roadside signs, signals, fixed objects, and other motorists either along the roadway or at intersections and driveways.”
Just as for Ohio DOT officials, visibility is a top priority for many state transportation departments when planning vegetation management.
“The main purpose of the program is to provide a safe travel corridor,” says Craig Dusablon, landscape coordinator for the Vermont Agency of Transportation (VTrans), which is based in St. Albans. “Clear zones are established for vehicle recovery and snow storage. Sight distances are cleared for passing zones and sign visibility. Hazardous trees and trees that may interfere with utilities are removed. The secondary purpose is for aesthetics and wildlife habitat.”
VTrans uses both mechanical and chemical vegetation management on its right-of-way areas. “Mowing on the interstate system is done twice per year and on the secondary as necessary, usually at least twice per season. Herbicide is used on an annual basis, primarily for control of vegetation beneath guardrails, poison ivy control, and control around aviation equipment at our state-owned airports,” says Dusablon. “Brush work is typically done in the fall or winter months.”
Herbicide treatments vary among the state transportation departments. This is due in part to the effort to keep the type of desired vegetation protected within the right-of-way areas in various North American climates.
For example, David Ross, technical manager for lawn and garden at Syngenta, based in Greensboro, NC, explains that some vegetation management programs incorporate pre-emergent herbicides, like the company’s Endurance, which can be used to control crabgrass and specific weeds along roadsides as well as in flower plantings.
Nonselective herbicides, such as the company’s Reward and Touchdown, are often implemented in vegetation management programs that require “taking out existing vegetation” and beginning a new planting, says Ross.
“Both of those have a zero-hour plant-back time. They don’t have any residual activity in the soil,” he explains. “Endurance does. It creates a barrier in the soil. They [the targeted invasives] become inhibited and don’t emerge. You re-seed the following season.”
Following a period of unusual weather, the New Hampshire Department of Transportation (NHDOT) has used vegetation management techniques primarily along new road construction areas and restoration along rivers that had been flooded.
“We’ve had two record-breaking rainfall years,” says Guy Giunta, landscape specialist supervisor for the roadside development section of the NHDOT. “That’s very unusual.”
Burning bush, Norway maple, and Japanese barberry are among the plants the NHDOT avoids because of their invasiveness. Japanese knotweed, bittersweet, and buckthorn are also invasives that have posed challenges for the department where mowing and cutting remain the primary right-of-way vegetation management methods.
“We are pretty much planting all native plant material, 3- to 4- or 4- to 5-foot shrubs,” says Giunta. These natives include highbush cranberry plants and pussy willows, because they are low enough to protect visibility and are not invasive.
Knotweed and ailanthus are two invasive, fast-growing species PennDOT battles in its approximately $25 million annual roadside vegetation management program. The program’s goals include maintaining highway safety, protecting pavement and signs, and keeping drainage areas clear, according to Ferguson. Mowing, brush and tree cutting, and herbicide use in combination with stump treatments are the main vegetation management methods used by the organization. The frequency of these treatments varies both with the road, which may need three to five mowing cycles a year, and herbicide treatments that are usually applied in two- to three-year cycles, says Ferguson.
In Iowa, noxious weeds, as defined by a state code, must be managed. “Most of them are perennials, so they can’t be controlled by mowing. You can mow them if it’s the wrong time of year to spray [herbicide],” says Mark Masteller, chief landscape architect for the Iowa Department of Transportation (Iowa DOT), which is based in Ames, IA. “It is our practice to use native plants on all rural construction projects.”
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Photo: DuPont |
| Low-volume backpack herbicide application targeting unwanted tall trees |
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Photo: Iowa DOT |
| Roadside vegetation management |
In one program, workers identify non-native vegetation along roadsides, kill the non-native vegetation, and then introduce native vegetation for the tall grass prairie region, including big bluestem, little bluestem, and Indian grass. Blazing star, gray-headed coneflower, monarda, and black-eyed Susan are some native wildflowers that are introduced, according to Mastellar.
Iowa DOT workers mow a swath along the edge of pavement for safety purposes, both to allow drivers to see animals and to prevent snow drifting.
“The budget has reduced, although I would say that mowing has been reduced less. Herbicide use has been reduced more,” says Mastellar. “I think it’s budget driven.” The Montana Department of Transportation (MDT) has an IVM approach that encourages desirable vegetation to curb unwanted weeds or tall-growing plants. More than 95% of the seeds used to reclaim the state roadsides through a reseeding program come from about 50 different varieties of native species. Weed infestations are actively monitored and mapped by the department, which, in special circumstances, works in coordination with county weed districts to prevent weed infestations from spreading.
“Our objective is to establish a dense, self-sustaining plant community at the soonest possible time following construction,” says Phil Johnson, a botanist for the MDT. “The plant community should be resistant to weed invasion, contain or eliminate sedimentation into our waterways, allow unrestricted driver visibility, and not draw wildlife to the roadside.”
The department uses IVM strategies, including biological controls. In 2006, the MDT funded a project costing approximately $25,000 of the organization’s noxious weed budget, through which 10 high schools raised and released these controls on department right-of-way areas.
“The selection of species used in reclaiming our roadsides is based upon local soil and climatic conditions, as well as adjacent land use,” says Johnson. “More and more native species seed sources are being developed to fill the needs of reclamation projects.
“We acknowledge the importance of creating a proper growing environment for our desirable species so that they create a dense, competitive stand. In other words, if you want to suppress weedy species, you need to create a growing environment that the desirable species flourish in: the principle of competitive exclusion.”
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Photo: Zen Sutherland |
| Keeping kudzu at bay is a full-time job. |
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Photo: National Park Service |
| Workers in an Appalachian grassy bald |
In Oregon, sections of the vegetation management program performed by the state transportation department are required by law.
“The state department of agriculture has a list of noxious weeds they have to control. We’re also required to have an integrated vegetation management program, where we use every tool that’s available,” says Will Lackey, vegetation management coordinator for the Oregon Department of Transportation (Oregon DOT). This includes using mechanical, chemical, cultural, and biological means to maintain vegetation for shading, sight distance, fire prevention, and tree hazard prevention.
“Most of the time we use native grasses. On some mitigation sites we use some native trees and some native shrubs, like Oregon grape,” says Lackey, adding that some native trees like the western red cedar are used. “We try to mix [natives] in wherever we can. In some places we still use non-native.”
The Oregon DOT works with the state’s department of agriculture on a biological control for vegetation management, releasing insects including beetles and weevils.
“We mow, and we spray, and we do a lot of mechanical shoulder blading. For your basic labor we use inmate crews,” says Lackey. “For our shoulders, we try to keep a bare shoulder so we use herbicide about once annually.”
In the urban areas, mowing takes place about two to three times annually, with more frequent mowing taking place in the wet, western side of the state. Mowing on the very dry, eastern side of the state, in general, is less frequent.
In addition to safety and preservation, aesthetics is an important aspect of the Florida Department of Transportation’s (FLDOT’s) vegetation management program.
“The department is made up of seven regional district offices and the Turnpike Enterprise. Each district has different soil types, plant varieties, and climate conditions,” says Tim Allen, maintenance rating program and roadside manager for the FLDOT, based in Tallahassee. “There has been an increase in the spread of undesirable and invasive vegetation within our rights of way,” says Allen. “By procedure, each district has to develop and maintain a turf management plan. The plan has to address the following major components:soil testing, soil amendments, mowing, herbicides, aeration, and control of invasive species. The department has a maintenance rating program in place to track the progress of each district. This program selects random sample points along our roadways. A two-member team rates up to 36 different roadway characteristics for each sample point.”
Landscaping, tree trimming, slope mowing, and roadside mowing are included in the characteristics currently listed for consideration under the vegetation and aesthetics element of the process, he explains. The FLDOT, which had a 2006 vegetation management budget of approximately $46 million, encourages the use of drought-tolerant plants as part of the vegetation management program.
Utility Easements
An easement that allows access to a utility is an example of a right of way requiring particular landscape sensitivity. Mark Rice with DuPont Vegetation Management and Forestry based in Chambersburg, PA, advises clients from Virginia to Maine with regard to what IVM strategies will work best for them. Although for new road construction, vegetation management programs must consider what grasses to plant to establish vegetative cover, Rice says that in utility right-of-way areas, vegetation management plans evaluate an area typically covered with many tall-growing, capable species in a wire zone that must be removed and replaced.
“We’re really looking to release the native species that have been crowded out, shaded out, by this competitive vegetation,” he says. “We use mechanical methods and chemical methods and try to reclaim the right of way. If we can create a right of way that has desirable understory or ground species, they actually prevent the germination of the tall-growing trees. They will outcompete the seedlings.”
Bringing an area back from a higher level of vegetative natural succession to a lower one, similar to what would naturally occur in an area after a fire, is much more successful than trying to establish a native species in the utility right of way, explains Rice. When vegetation levels advance to the tree stage, this crowds out and drives away desirable grass and forbs. But when a right-of-way area is returned to the grass and forbs level, he says, it creates the right habitat for mice and voles.
“Their chosen food is seeds and seedlings,” says Rice, describing this as a form of biological control. “They’re eating and devouring the seed source of these tall-growing, unwanted trees. We’ve also created a habitat for turkeys. They like insects. You bring back the deer. There’s more food available for them.”
Rice helps create plans for people working to bring their vegetation levels back. Utilities, for example, hire foresters. Their vegetation management plans are written based on voltage level of the lines and include different clearance requirements and the frequency of an area’s cycle time. Growth rates in Rice’s area, for example, might range from four-year to six-year cycles.
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Photo: National Park Service |
| There are over 1,000 vistas to maintain on the Blue Ridge. |
“Every cycle period, go back to that line,” he says, explaining that a vegetation management method depends on growth usually described by the height and density of unwanted vegetation. “If it’s low-density and shorter brush, we’ll use backpacks. If it’s taller and more dense, we may use a directed hydraulic application and directly spray on the unwanted species. If it’s out of control, we’ll have to come in and mechanically clear it.”
After a stable understory has been established by a second or third cycle, and as the unwanted species continues to decline, smaller amounts of spray are required, Rice explains.
“You would apply a lower total volume,” he says, noting that on the second cycle, a backpack application may be performed to selectively target the undesirable species. “[If the application was] 20 gallons on the second cycle, it may be only 10 gallons on the third cycle. That’s what we’re all aiming for.”
Protecting National Treasures
A drive through the two-lane Blue Ridge Parkway, a 470-mile national park stretching south from Shenandoah National Park in Virginia to the Smoky Mountains National Park that straddles the border of North Carolina and Tennessee, allows visitors beautiful views. There are about 1,000 scenic locations along the curving paved road, according to Chris Ulrey, a plant ecologist and vegetation specialist at the Blue Ridge Parkway, based in Asheville, NC.
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Photo: Oregon DOT |
| A planting using native material including sword fern, red twig dogwood, Pacific ninebark, and snowberry |
“At select places we cut that vegetation to provide views,” he says, explaining that these vistas can range from about one-tenth of an acre to 3 acres. “Basically, we cut everything. We do that about every three years. Traditionally, we did all that by hand.
“We’ve started applying herbicide to the stump at the top edge of the cuts, trying to guard against the rapid regrowth of the species. You can cut a lot of these woody plants and they will re-sprout and block the view.”
Known as the Vista Management Program, the work is contracted out with a budget of approximately $300,000. The amount of herbicide used is limited, says Ulrey, and is used to combat exotic plants, including tree of heaven and princess tree, that have invaded the vistas. The parkway crosses the large urban centers of Roanoke, VA, and Asheville. Ulrey says people in those locations were basically planting “what maybe they shouldn’t plant,” and the seeds from this vegetation have blown into the park.
In a natural area in the park near Asheville called Craggy Gardens, with an elevation of 5,000 feet, lies grassy balds, or big open fields located at the top of the southern Appalachian mountains.
“They [the big open fields] are natural occurring communities. The early European settlers thought it would be a logical place to graze their cattle. When you look at the mountain from a distance, it looks bald,” says Ulrey. “There are no trees on it. It’s native grasses and sedges. When the national parks purchased the lands, all the grazing stopped, invaded by native woody plants, and eventually these will all be forests.”
A variety of rare species occurs in the balds, and managing and maintaining the open area has posed a challenge for the park workers. Because the balds were created through native animal grazing, explains Ulrey, mowing is used to manage the area’s vegetation.
“We use walk-behind brush mowers and Weed Eaters to do this work. We think it basically simulates grazing,” says Ulrey, noting herbicides are not used in the area. “In an ideal world we’d bring buffalo and elk back and turn them loose up there. In this day and age, it’s just not a realistic option.
“We mow twice a year every three years,” he continues, explaining that this mowing takes place in early summer and then again in late summer. “It’s a strategy to exhaust the energy resources of the woody plants. We do it in-house. We’re doing about 20 acres of this type of habitat. It takes about three weeks times a crew of four people about $10,000 to $15,000 in personnel costs.”
At AcadiaNational Park in Bar Harbor, ME, part of the vista management program involves performing cut stump treatments with Garlon herbicide. Merle Cousins, the roads maintenance foreman at Acadia, says herbicide is used only when treating stumps, and mowing is the most common vegetation management method.
“We do roadside mowing along the ditchlines and on the back slopes. It’s about 4 feet of the road shoulder,” says Cousins. “We mow once a year for the roadside mowing. Our groundside mowing is as needed.”
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Photo: National Park Service |
| Vegetation is cut back every three years on the Blue Ridge Parkway. |
Invasive plants, such as purple loosestrife, are one of the primary reasons for vegetation control at the park, according to Geneva Langley, a botanist at the park.
While mowing and cutting are the primary form of vegetation management for rights of way at the park, prescribed fire is used for vegetation management in the vista management program on monitored plots.
“We don’t [mind] using prescribed fire to maintain rights of way,” says Doug Jones, fire management officer at the park. “Our objective is to use fire where appropriate to maintain the open vistas. When you cut mechanically, sometimes you actually stimulate more growth. Like a maple, sometimes you can end up getting even more shoots from that stump. One of the ways you can reduce that over time is through fire. It will cause the root system to die.”
Prescribed fire can also be cost-effective. “They would have to look at what the vegetation is that they want to burn, keep historical management in mind—and keep safety in mind,” says Langley.
In the park’s wetlands, vegetation is managed with a foliar application of herbicide. “We use a 1% glyphosate solution,” says Langley.
Native plants and grass seed are used for plantings. “We use native plants for restoration. We use genetically native plants,” notes Langley. “Red or white spruce we plant quite frequently.”
Municipal Maintenance
In Alabama, the Calhoun County Highway Department is working toward a Bermuda grass release program. Brian Conary, the administrative services manager for the department who is based in Anniston, AL, says the organization is helping the Bermuda grass thrive by “taking out its competition.” The area has had a problem with Johnson grass in the past, and Bermuda grass is favored for visibility purposes because it won’t grow higher than 6 inches.
“It’s a program that the state, our county, and several of the counties have been trying to do for years,” says Conary, adding that the herbicide costs for the program last year were $165,444 and the program’s mechanical budget was $238,990. “There have been changes in the herbicides that we use targeting particular weeds. When you take something out, there is always something else that takes its place. When we take out the Johnson grass, then we have a problem with the foxtail.”
Spraying is done three separate times during the spring and summer months to eliminate enemies of Bermuda grass. There is no active planting as a part of the program.
Controlling vegetation in city right-of-way areas, particularly curbs, gutters, and sidewalks, is a challenge the City of Lakeport, CA, meets with mowing, spot-spraying, brush cutting, and manual removal.
“We have a year-round program. Heavy brush trimming or removal is done once or twice a year depending on the growth rate in a given year,” says Doug Grider, the public works superintendent for the City of Lakeport, adding that the city uses Ukiah, CA–based NTech Industries’ WeedSeeker, a selective sprayer, as part of its vegetation management program. “The WeedSeeker setup we are using basically replaces a person and truck that used to drive around and spray weeds invading curbs, gutters, and sidewalks. Another advantage of the WeedSeeker is that it only sprays when it detects a living weed or plant, which means a large cost savings over broadcast spraying.”
Though city workers perform very little planting during the year, Grider says native plants are required for any planting that is completed.
Going Native
One of the most common trends in right-of-way vegetation management is, in a sense, a return to a region’s past. Dusablon of VTrans says he sees an increasing use of native plants in vegetation management programs, and possibly decreased use of herbicides.
“We are working with the Natural Resources Conservation Service on developing native plants for our rights of way,” he says. “Our plantings, whether native or non-native, are chosen by a performance measure. We have developed a technical manual that addresses critical area plantings using both native and non-native plants and seeding techniques.”
Ferguson says PennDOT is also increasingly using natives. “We are incorporating more and more native plants in our plantings,” he says, adding that many times they don’t grow as quickly as needed to prevent erosion. “[So] we’ll mix native plants with non-native.”
Switchgrass and little bluestems are among the natives PennDOT uses. “They seem to perform the best in our climate,” says Ferguson. “We need the combination to get the growth and the cover that we need.”
Conflicting attitudes toward the use of herbicides in vegetation management programs persist in some select areas.
“The government is hesitant to spray, [while] the industry is saying, ‘We understand your concern, but we’re losing control of our invasives,’” says Giunta, adding that the latter group is referring to safe and effective herbicide programs.
Lucas of the Ohio DOT notes, “We have been working more with using plant growth regulators [PGRs]. Plant growth regulators and certain herbicides slow down the growing process of plants, such as grass, and also reduce seed head production. We are hoping to reduce the number of mowing cycles each year through the use of PGRs. A pilot program we ran in a couple of our District 5 counties has shown a marked cost savings.”
For now, the IVM approach continues to be an effective way for most right-of-way vegetation management programs as they face challenges combating invasive species that threaten both landscapes and safety throughout the United States.
Based in Morgantown, PA, Tara Beecham writes frequently for Erosion Control.
EC - July/August 2007
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