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County weed commissioner warns of growing Japanese knotweed problem, proposes tracking and roadside control
Summary
Acting weed commissioner Tyler Kelly told supervisors he has documented increasing Japanese knotweed across county rights-of-way and near bridge infrastructure, recommended a tracking program and discussed roadside spray options; the board filed the required 2025 weed-commissioner certification.
Tyler Kelly, planning and zoning county sanitarian and acting Marshall County weed commissioner, told the Board of Supervisors that Japanese knotweed populations have increased across Marshall County and pose infrastructure risks.
"I have been seeing an increase in Japanese knotweed throughout the county," Kelly said. He described the species as difficult to control, resistant to some herbicides, and prone to spreading when mowed: "When you mow it, it spreads, heavily, and I'm seeing it in areas that I definitely do not want to see it in," including near bridge embankments where root growth can separate concrete joints.
Kelly reported outreach to landowners and Marshall County Conservation, recommended starting a tracking program for the species, and said a roadside spray program could address other invasives such as leafy spurge. He referenced a product used in Story County called Polaris (a soil sterilant) as one approach but noted long soil half-life and tradeoffs. Conservation director Emily Herring raised concerns about residents dumping cut plant material into ditches, which contributes to spread.
The report was filed as the 2025 county weed commissioner certification required by state law; the board moved and carried approval and authorized the vice chair to sign.
Kelly and staff said they will continue outreach, tracking, and interdepartmental coordination to develop a control plan and identify funding or resource needs.
