Transportation Department works with OSU to save monarch habitat
STILLWATER — A new voice may influence when and where the Oklahoma Department of Transportation decides to mow along the highways in the future, and it comes from a simple weed.
It’s milkweed, which is the lone host plant for the monarch butterfly.
With growing concerns about the shrinking monarch population, which migrates through Oklahoma annually, a six-state collaborative formed under the Federal Highway Administration and in 2016 designated the Interstate 35 corridor as the “Monarch Highway.” From Texas to Minnesota, state agencies are looking into best practices to foster the growth of milkweed species and raise awareness about the butterflies and other pollinators.
Oklahoma comes into the picture as one of the first places where northbound monarchs will lay eggs in the spring, and one of the last where a final generation may hatch for the long trip south to Mexico for the winter.
The plants provide all the nutrition the caterpillars need and compounds in the plant give the larvae and the butterfly toxicity and a bad taste, thus their bright coloration as a warning for predators, field guides note.
The Transportation Department has been doing its part along I-35 and other roadways across the state to help milkweed thrive.
“We’re doing what we can to keep those roadsides so people can travel safely, and to also promote the growth of milkweed and habitat for pollinators,” said public information manager Lisa Shearer-Salim.
The Transportation Department used to mow roadsides four times a season but already has cut back in many places to doing only “safety mows” early in the season and delaying full-width mowing on rights of way until late June or early July.
Examples of “safety mows” include mowing grass and weeds close to the roadway to help prevent fires and provide safe places to pull well off the road for emergencies, and at intersections where tall vegetation might obstruct vision, Shearer-Salim said.
“Another exception is in the metro areas we do full mows sooner because of the intensity of traffic and to keep sight lines clear,” she said.
The department also is in touch with the Oklahoma Monarch and Pollinators Collaborative, or “Okies for Monarchs,” and on Friday worked with that group to expand a large butterfly garden at the state visitor center on I-35 in Oklahoma City. The 20- by 40-foot plot is a designated Monarch Watch Waystation, she said.
“Generally the goal is to mow less during the time the monarchs are laying their eggs, April-May and September-October,” Shearer-Salim said. “We’ll try to do full mows in the July-August time frame and then one at the end of October to get ready for the next year’s growth.”
The Transportation Department partnered in 2016 with Oklahoma State University to research what mowing regimens will work best to encourage growth of milkweed while keeping roadways safe.
A few species of milkweed are native to Oklahoma, but the most common is Asclepias viridis, sometimes called green antelope horn, green milkweed or green antelope horn. The monarchwatching crowd just calls it “viridis.”
Reports on Facebook pages of “plenty of viridis” along roadsides were common this spring. Experts say that whether it was just a good year for viridis or whether the mowing changes already are making a difference is unknown.
Off State Highway 51 just west of Stillwater, behind a sign designating the area as “Research and Training Habitat” with the emblem of a bright orange-and-black monarch, OSU professor of integrative biology Kristen Baum walked a plot Friday that is about 175 yards long and 25 or 30 yards wide with dozens of orange and pink flags noting where milkweed plants stood.
“This was just a very good milkweed spot and a great place to put one of our research plots,” she said.
Over the 170-some yards, the grasses and weeds are of varying heights and the milkweed in various stages of growth.
One section represents the traditional way the Transportation Department used to mow, with four mows per season. Another is hit just in mid-July (after the milkweed goes to seed), one is mowed in July and in the fall, one gets the fall mowing only, and another is mowed in mid-June and will be mowed again in the fall.
OSU researchers visit the plots, of which there are 25 scattered along State Highway 51 and I-35, to track the progress of vegetative growth of the milkweed — right down to the point of measuring stems.
“The weather year-toyear of course plays a big role, too,” Baum said. “This year in early spring, there was hardly any growth because it was cold so late in the year, but they did grow and now a lot of them went to seed earlier than usual.”
Milkweed fans shouldn’t be too concerned about July mowing for milkweed because the majority of the plants have disseminated their seeds and are in decline. However, limbs and leaves do regenerate from the mowed-off stems — possibly providing new tender growth for fall migrants.
Baum said there still is much to learn, and what mowing regimens or other measures will be found along the way are yet to be determined.
“We keep coming up with more questions, but that’s a good thing,” she said.
For the Transportation Department, it’s an effort that the agency expects can make a difference.
“It is a concerted effort,” Shearer-Salim said. “With our department owning that much property, it makes us a player in managing the state’s land.”