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 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 NormanTualatin 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.