• Skip to main content
Tualatin Soil and Water Conservation District Logo
  • Our Priorities
    • Clean and Abundant Water
    • Healthy Soil
    • Food & Farms
    • Thriving Habitat
    • Invasive Species Management
    • Resilient Forests
  • Our Programs
    • Rural Conservation
    • Urban Conservation
    • Forest Conservation
    • Habitat Conservation
    • Invasive Species
    • Conservation Education
    • Grants & Funding
  • Get Involved
  • Stay Informed
  • Subscribe
  • Our Story
  • Search
Home / News / Stay Informed / Milk Thistle: A Prickly Problem in the Tualatin Watershed

January 4, 2021

Milk Thistle: A Prickly Problem in the Tualatin Watershed

SWCD Branded Separator
Milk thistle flower. Photo Credit: Jan Samanek, Phytosanitary Administration, Bugwood.org

January 2021’s Weed of the Month is milk thistle!

Thistles are nothing new. We have been digging and pulling these pesky, prickly plants in our gardens and natural areas for a long time. For those less familiar with invasive thistles, these weeds can be particularly tricky to eradicate due to the thousands of seeds they produce and their ability to regrow after being mowed or cut.

Recently, there has been an uptick in milk thistle reports throughout Washington County – an alarming development!

  • Milk thistle rosettes
  • Milk thistle dead flowers
  • Milk thistle infestation
Milk thistle rosettes, dead flowerhead, and infestation. Photo Credit: (Top) Tualatin SWCD. (Bottom) Jan Samanek, Phytosanitary Administration, Bugwood.org

Milk Thistle Impacts

Agricultural areas are particularly susceptible to milk thistle. Crop fields and pastures are prime habitat for it, and heavy equipment, such as tractors, can bring seeds from other locations when not properly cleaned.

Not only does milk thistle crowd out crops and decrease farmer’s harvests, but it’s also toxic to livestock due to the high concentrations of nitrate. It can also injure livestock and people with its long spines.

Notes from the Field

Tualatin SWCD’s Invasive Species Technician, Trevor Norman, on his experiences surveying and controlling milk thistle:

The fog has begun to lift from the ground, only to reveal a field covered in lettuce-like tufts of vegetation. Completely covering around an acre of what was once prime horse pasture, this spiny thistle has rendered a portion of this field completely useless, quarantined from horses for their protection. It would be impossible to pull all these plants individually. Instead, it will take several seasons of herbicide treatment and years of monitoring to make sure this pasture is restored to a usable state. A small portion of this infestation has gone to flower and set seed. Gloomy, dead flowerheads hang before opening to release their seeds. I break out the trusty pair of loppers and begin cutting to prevent the seeds from spreading. Even when dead these spines are still capable of poking and inflicting pain!

TREVOR NORMAN – Invasive Species Technician

Trevor Norman

Tualatin SWCD Invasives Species Technician

How You Can Help

It is important that new infestations are reported quickly before they have a chance to grow and spread. While smaller infestations can be hand pulled, larger colonies must be treated with herbicide and monitored for many years.

If you believe you have spotted milk thistle in Washington County, please report it to the Oregon Invasives Hotline and we will respond and help get the infestation under control.


« Farm Transition Planning – Why is it So Important?
Where Do Pollinators Go in the Winter? »

Article By: Trevor Norman, Invasive Species Technician

Posted In:

Invasive Species, Invasive Species Management
SWCD Branded Separator

Share:

Share on Facebook Share on Twitter Share on Pinterest Share on LinkedIn Share on Email
Subscribe News Icon

Email me about caring for the soil and water!

Get Involved Icon

Find an Event

Calendar of Events
Upcoming Workshops

reflection in a lake

About Us

  • Our Story
  • Our Watershed
  • Our Staff
  • Our Board
  • Careers
  • Reports & Publications

Resources

  • Event Calendar
  • Weed & Pest Directory
  • Contractor Directory
  • Library & Videos
  • Tool Loan Program
  • News
  • Watershed Navigator

Contact Us

Tualatin Soil and Water
Conservation District
7175 NE Evergreen Pkwy #400
Hillsboro, OR. 97124

Phone: 503-334-2288
Office Hours: 8:00am - 4:30pm
Email Us

Follow Us

العربية العربية 简体中文 简体中文 繁體中文 繁體中文 English English Filipino Filipino Français Français Deutsch Deutsch हिन्दी हिन्दी 한국어 한국어 Русский Русский Español Español Tiếng Việt Tiếng Việt

© 2023 Tualatin Soil and Water Conservation District. All Rights Reserved. | Sitemap | Non-Discrimination Policy | Privacy Policy | Website Design by Hoopla Creative

 

Loading Comments...