Invasive Species/Vegetation

A recent study conducted by the University of Minnesota and funded by the Minnesota Local Road Research Board determined that roadside plantings, particularly “turfgrass,” tend to do better when they are both biodiverse and carefully matched to their ideal growing conditions.

[Above photo by the Minnesota DOT]

University researchers noted in a blog post that roadside turfgrass serves the important roles of reducing soil erosion, pollutant runoff, and the spread of invasive weeds, as well as adding visual appeal. However, maintaining it along Minnesota roadsides is difficult because of the harsh climate and roadway maintenance practices, such as road salting and snow plowing in the winter.

“That’s why developing tools for practitioners to make better decisions on revegetating roadsides will save financial resources for Minnesota DOT, practitioners, and local communities,” noted Eric Watkins, a professor with the school’s Department of Horticultural Science and the principal investigator for this study.

The university’s researchers set up 14 test plots along Minnesota roadways and tested 44 treatments mixes. What they found matched up with existing literature compiled from similar reasearch: Biodiversity correlates to better vegetation cover and a decrease in weeds.

“The use of species mixtures, compared to monocultures, has been shown to have multiple benefits,” Watkins noted. “These include more coverage of the seeded species, reduced disease frequency and severity, and extended green color.”

The reason is likely because, within the diverse species mix, the plants have a variety of adaptations and tolerances and thus can survive a wider array of conditions than a single species could, he said.

Yet one “immediate downside” of biodiversity is complications arising from every plant species and subspecies having “wildly different germination rates, rooting depths, and moisture and temperature tolerances,” with interaction among species changing those things even further.

To make it easier for practitioners to implement biodiverse seed mixes, University of Minnesota researchers categorized state roads into three “seeding clusters” – regions based on growing conditions such as temperature, moisture, and soil quality. Two of the seeding clusters are geographic (north Minnesota and central/south Minnesota), with the third is categorized as “poor soil quality” or soil that is sandy, low in organic matter, etc.

“Establishing these test plots with seed mixes that vary by region was an important step in finding the most effective and climate-resistant roadside turfgrass,” explained Dwayne Stenlund, erosion control specialist with Minnesota DOT’s Erosion Control and Stormwater Management unit and the study’s technical liaison.

Moving forward, Watkins said his research team plans to make a web-based version of this seeding “budgeting tool” so it’s easier for local government agencies and the Minnesota DOT to use. They also plan to do more long-term studies at the test plots – their current research only lasted two year – as future seed testing will need to take climate change into account.

“Implementing these mixtures will reduce soil erosion, improve aesthetics, save local communities’ financial resources, and improve the overall environment we occupy,” Watkins added.

Many states are involved in an array of roadside vegetation research to make a variety of environmental improvements.

For example, the Illinois Department of Transportation recounted in a November 2022 blog post how it changed its mowing practices over the years to better protect roadside landscapes that are vital to pollinators and native planet life.

The agency said it adopted mowing policies to protect the habitat and migratory patterns of the monarch butterfly and other pollinators that use it as a food source. That policy allows for mowing of the state’s roads in a four-year rotation during the summer.

Meanwhile, ecologists at Idaho State University are working with the Idaho Transportation Department to turn state roadsides into veritable “Swiss army knives” of vegetation so they are both more fire-resistant and more welcoming to pollinating insects.

Those ecologists are working with three different types of ecosystems at those sites, figuring out how to make the land more hospitable to native plants and less so for invasive weeds. That research also includes increasing the habitat’s fire resistance, while becoming a more attractive habitat for pollinators like bees and butterflies.

The Pennsylvania Invasive Species Council or ISC is preparing to pilot test an invasive species management program this summer – and the Pennsylvania Department of Transportation is one of several state agencies on tap to play a key role in that pilot test.

[Above image by PennDOT]

The program is built around findings from the first statewide survey of impacts from invasive plants, insects, pathogens, and animals, ISC conducted in late 2022 – the Pennsylvania Invasive Species Impacts Survey.

“A biodiverse native ecosystem provides the natural resources that are essential to our lives, from agricultural food production to outdoor recreation and fishery, timber, and other industries,” explained Rich Negrin, acting secretary for the Pennsylvania Department of Environmental Protection, in a statement.

He added that the ISC believes a statewide program is necessary to respond to growing number of invasive species in Pennsylvania – including the spotted lanternfly, mile-a-minute vine, Japanese stiltgrass, barberry shrub, zebra mussels, and many others.

The pilot will bring together expertise from local and state government, industry, community, and academic organizations to create a Partnerships for Regional Invasive Species Management or “PRISM” program.

The Council and the Pennsylvania Association of Conservation Districts or PACD will partner to pilot-test a small-scale version of a PRISM program in 13 northwest counties in July.

Using $210,000 from the U.S. Department of Agriculture Forest Service, PACD plans to conduct on-the-ground projects to remove invasive species and conduct educational outreach to help prevent the introduction of invasive species. In addition, PACD will develop a strategic plan identifying priorities and committed partners for the region – including PennDOT.

“PennDOT has worked with federal, state, and local partners to encourage native plant growth and target invasive species in our right of way,” noted Mike Carroll, acting PennDOT secretary. “We look forward to continued partnership through this council to address this statewide challenge.”

Other state departments of transportation are also engaged in efforts to eradicate a variety of invasive species in their regions to improve protections for native plant and animal life, as well as encourage pollination efforts.

For example, the Kentucky Transportation Cabinet recently began cranking up its annual weed control program to keep a dozen unwanted and noxious weeds from encroaching on the bluegrass state’s transportation infrastructure.

Meanwhile, in November 2022, the Illinois Department of Transportation recounted in a blog post how it changed its mowing practices over the years to better protect roadside landscapes that are vital to pollinators and native planet life.

The agency has adopted mowing policies to protect the habitat and migratory patterns of the monarch butterfly and other pollinators that use it as a food source. That policy allows for mowing of the state’s roads in a four-year rotation during the summer.

Finally, in October 2022, ecologists at Idaho State University began working with the Idaho Transportation Department to turn state roadsides into veritable “Swiss army knives” of vegetation so they are both more fire-resistant and more welcoming to pollinating insects. They are working with three different types of ecosystems, figuring out how to make the land more hospitable to native plants and less so for invasive weeds.

The Kentucky Transportation Cabinet is cranking up its weed control program to keep a dozen unwanted and noxious weeds from encroaching on the bluegrass state’s transportation infrastructure.

[Above photo by KYTC]

Weeds are more than a gardening nuisance; they can obscure sightlines, compromise drainage, wipe out native plantings, and kill off roadside turf, leading to roadbed erosion and serious maintenance issues.

“Some weeds are highly destructive and difficult to control,” said Naitore Djigbenou, executive director of the KYTC Office of Public Affairs.

“Weeds clog storm-water drainage systems and can compromise pavement and structures which can lead to potholes and structures failures,” Djigbenou noted, which is why KYTC uses Integrated Roadside Vegetation Management or IRVM to “suppress and control noxious and invasive weeds on state-maintained highways.”

Weed control is accomplished through mowing, turf-grass establishment, insect biological control, and the use of herbicides approved by the Environmental Protection Agency that are applied by licensed applicators.

“If left untreated, some weeds can grow several feet tall and impact driver visibility,” KYTC Secretary Jim Gray pointed out in a recent news release. “Actively treating the weeds on state-maintained property enhances safety, prevents damage to ditches and drains and minimizes the presence of plants that attract deer near highways,”

The agency also reaches out to private landowners, he said, encouraging them to request that highway crews treat some noxious weeds on adjacent state-owned right-of-way.

Kentucky law dictates which 12 plants are considered “noxious weeds” that should be eradicated. They are Amur Honeysuckle, Canada Thistle, Common Teasel, Cutleaf Teasel, Japanese Knotweed, Johnsongrass, Kudzu, Marestail, Multiflora Rose, Nodding Thistle, Poison Hemlock, and Spotted Knapweed.

Noxious weeds often invade and destroy the roadside turf grass, leaving those areas vulnerable to erosion, KYTC added. They can also smother native plants through rapid reproduction and long-term persistence. Twenty years ago, the Federal Highway Administration published a compendium of resources aimed at removing invasive species of plants that might take root along roadways nationwide. They can cause “significant changes” to local ecosystems, upsetting ecological balances and causing economic harm to the country’s agricultural and recreational sectors.

The Kentucky Transportation Cabinet is gearing up to control the growth of noxious and nuisance weeds along roadsides throughout the state starting in April.

[Above photo by the KYTC]

KYTC is targeting targets 11 noxious weeds with this effort: Johnson grass, giant foxtail, Canada thistle, nodding thistle, common teasel, multiflora rose, Amur honeysuckle, poison hemlock, marestail, Japanese knotweed, and kudzu.

KYTC added that local property owners may file a request that highway crews treat select nuisance weeds found on adjacent state-owned rights of way as well. To request weed treatment request submit a written application to the local KYTC highway district office, the agency added.

“Weeds are more than a nuisance-they pose safety concerns,” explained KYTC Secretary Jim Gray in a statement.

“Actively treating the weeds on state-maintained property enhances driver visibility near roadways, prevents damage to ditches and drains, and minimizes the presence of plants that attract deer near highways,” he said.

Noxious weeds often invade and destroy the roadside turf grass, leaving those areas vulnerable to erosion, KYTC added. They can also smother native plants through rapid reproduction and long-term persistence.

Twenty years ago, the Federal Highway Administration published a compendium of resources aimed at removing invasive species of plants that might take root along roadways nationwide. They can cause “significant changes” to local ecosystems, upsetting ecological balances and causing economic harm to the country’s agricultural and recreational sectors.

The Connecticut Department of Transportation is working with the U.S. Department of Agriculture, the Connecticut Agricultural Experiment Station, and the Connecticut Department of Energy and Environmental Protection to battle an invasion of the “spotted lanternfly,” which could severely affect the state’s agricultural crops – particularly apples, grapes, and hops, and ornamental trees.

[Above photo via Wikimedia Commons]

The spotted lanternfly – formally known as Lycorma delicatul – is not actually a fly, but an exotic and invasive sap-feeding planthopper that feeds on more than 70 species of plants. The preferred “host” of the spotted lanternfly is a plant known as “tree-of-heaven” or “Ailanthus altissima,” which itself is highly invasive and abundant along highways, in urban areas, and along the edges of agricultural and industrial areas.

The agency said in a statement that the concern is that the feeding of spotted lanternfly nymphs and adults on sap from trees and vines weakens the entire plant, while the excretions from these leaf-hopping insects encourage the growth of black sooty mold, thereby reducing photosynthesis.

As a result, agricultural crops face reduced yields due to the lanternfly’s feeding on fruit and general weakening of plants, if not destroying them outright.

To help combat the spread of this invasive species, the Connecticut DOT is spreading the word via informational posters and flyers at its rest stops about the spotted lanternfly invasion and is helping place traps in highway right-of-ways to help gauge the spread of this invasive pest. The agency added that it is training Connecticut field personnel in identification, reporting, and proper precautions to halt the spread of the lanternfly.

The agency also noted that during the months of August through November the adults of this pest can attach themselves or “hitchhike” on vehicles and trailers, so it is asking travelers to check their vehicles the lanternfly, and – if found – to take a picture, destroy the insect, and report it to The Connecticut Agricultural Experiment Station.

State departments of transportation across the country are regularly engaged in a variety of efforts to beat back invasive insect and plant species.

For example, Kentucky Transportation Cabinet highway crews engage in an annual effort – usually at the beginning of March – to control the spread of invasive plant species that can damage transportation infrastructure as well as interfere with motorist “line-of-sight.”

Such efforts sometimes involve usual tactics, as well. For instance, the California Department of Transportation launched a pilot project in February 2020 that used 300 goats for nearly a month to help remove invasive non-native weeds such as bur clover, mustard, and thistle from a 20-acre site adjacent to Highway 1 just north of the Piedras Blancas Lighthouse. Instead of relying on herbicides, Caltrans said the goal of this project is to deploy a “more sustainable approach” to revitalizing the native coastal prairie adjacent to a highway realignment project originally completed in 2017.

Kentucky Transportation Cabinet crews began treating for noxious and nuisance weeds along state roadways in March, with those treatments designed to help control the spread of “undesirable plants” along state highway rights of way to improve driver safety and ensure efficient maintenance operations.

[Photo by the KYTC.]

In particular, KYTC crews are targeting Johnson grass, giant foxtail, Canada thistle, nodding thistle, common teasel, multiflora rose, Amur honeysuckle, poison hemlock, marestail, Japanese knotweed and kudzu.

The agency added that those noxious weeds often invade and destroy the roadside turf grass, leaving these areas vulnerable to erosion. They can also smother native plants through rapid reproduction and long-term persistence.

“Left uncontrolled, noxious weeds can grow so large that they interfere with a driver’s line of vision on highways,” Jim Gray, explained Jim Gray, KYTC secretary, in a statement.

“Weed maintenance is important in preventing potential damage to pavement and embankments, as well as clogged ditches and drainage problems,” he said.

State departments of transportation are also experimenting with other forms of weed control as well.

For example, the California Department of Transportation – known as Caltrans – began using goats in early 2020 as part of a pilot project to control weeds within a 20-acre site adjacent to Highway 1 just north of the Piedras Blancas Lighthouse.

Instead of relying on herbicides, Caltrans is taking what it calls a “more sustainable approach” to revitalizing the native coastal prairie adjacent to a highway realignment project originally completed in 2017.

According to an agency statement, the project brought in 300 goats for nearly a month to help remove invasive non-native weeds such as bur clover, mustard, and thistle.

As an 11-mile reconstruction project along Interstate 10 between Interstate 17 and the Loop 202 gets ready to start, biologists with the Arizona Department of Transportation are preparing to relocate native plants out of the way.

[Photo courtesy of the Arizona Department of Transportation.]

The agency said its crews are identifying state-protected plants in the planned construction zone – such as ocotillo and saguaro and barrel cactus – and studying roughly 2,500 trees to identify native species, including palo verde, mesquite and ironwood.  

The Arizona DOT plans to relocate most of them into temporary nurseries during construction, transplanting them back to their roadside habitats when construction work is complete. 

“Protecting the natural Arizona environment is an important part of our work,” said Robert Samour, senior deputy state engineer and leader of Arizona DOT’s major projects group, in a statement.

“There were more than 1,000 plants along the South Mountain Freeway that we maintained for more than three years and replanted after construction to preserve the plants and the beautiful landscape,” he said. 

[The Arizona DOT conducted a similar relocation effort in 2018 for native cactus plants located near a bridge replacement project on U.S. 60 where that highway crosses Pinto Creek six miles from the town of Miami, which is a little more than 81 miles due west of Phoenix.] 

The Arizona DOT anticipates starting the I-10 reconstruction project this summer, relocating native plants and utility lines. The agency anticipates construction will be complete by late 2024, with the project ultimately improving travel time and safety, as well as easing access to Phoenix Sky Harbor International Airport and supporting local, regional, and state economic growth. 

The California Department of Transportation and its contractors are deploying a new tool to safely speed up the removal of dead, dying, and diseased trees throughout the state: Telescoping grappling saws.

[Photo courtesy of the California Department of Transportation.]

The agency said in a statement that such saws allow its crews and contractors to take trees down at a faster pace than traditional tree removal processes; completing that process with greater safety from the ground via remote control, well outside the fall zone for trees being removed.