Scott Rall: New top-line weed predators make thistles seem tame

Canada thistles are very unpopular weeds. But there's worse.

Scott Rall
Scott Rall

One man’s weed is another man’s habitat.

Man has been at war with weeds, I’ve called them annual and perennial vegetation for as long as we have had fire, I think. Weed control for ag producers over the past 20 years has been with crops that are resistant to a chemical called glyphosate. The common term most people recognize it as is “Roundup.”

The farm fields are sprayed with the chemical and it kills almost all of the weeds but leaves the corn or soybeans unharmed. There are some weed varieties that are becoming Roundup resistant, which means the chemical does not work on them as well as it used to.

Just about every weed is intolerable to an ag producer, and I understand why. High on the list is the Canada thistle. This weed plant is a perennial and comes back year after year if you don’t kill it dead. They spread seeds all over the landscape in numbers so high you could not count them all.

They are a broadleaf weed and can be killed with Roundup or other broadleaf herbicides like the good old stand-by 24-D. It is an opportunistic weed. Show me one space of disturbed dirt and by the end of the growing season it will be filled with Canada thistle.


The challenge when dealing with habitat and this aggressive weed is that most areas that are restored to wildlife habitat include plants that benefit pollinators like honey bees and monarch butterflies.

These native forbs and flowers are also broadleaf plants. If during the initial seeding and restoration of a wildlife area, you get a batch of Canada thistles that also grow in this new planting, you cannot spray them with a broadleaf killer without killing all of the desirable flowers and forbs as well.

When the grasses and flowers of newly-planted wildlife areas get fully established, they will for the most part, out-compete the Canada thistle and other weeds for survival -- and the weed issues decline dramatically. It is getting to be the norm, now, that all new plantings will get mowed the first year in order to keep the weeds that do get started from going to seed and spreading onto the neighbor’s property. This is a good idea and I fully support it.

There are a few other weeds that in my opinion should get far more attention than the veracious attention the Canada thistle gets. The first one is the plant called wild parsnips.

The plant grows from 2-5 feet tall and has yellow blossoms. The way to best identify it is that the stem of the plant is ribbed. If you rub up against the plant or try to pull one without gloves, many people will break out in blisters. The arms and hands of those affected looked just like they were burned with scalding hot water.

The plant really is a problem, and I am starting to see it all over the county.

When you mow it, all you do is spread the seeds down whatever path the mower takes. Mowing is the biggest cause of the spread, in my opinion. The plant is on the strict control list of noxious weeds.

The next one is even worse. It is called poison hemlock. It also grows from 2-5 feet and has white flowers. It is most easily identified by the small purple spots on its pale green stalk. These purple spots give way to a completely purple stalk when the plant matures.


Poison hemlock has been around for so long that a tea which contained some of its leaves was used to kill an emperor in Roman times. The plant is on the “exterminate with extreme prejudice” list of weeds.

If you pull either of these two plants and toss them on the ground, the seeds will still mature and germinate. They must be removed and burned or buried.

This hemlock plant showed up on my property three years ago and I have kept it at bay. I recently saw an entire stand of it on township property and took it upon myself to go kill it without mercy.

Spay and walk away does not work. I have had the entire plant bend over and the tip bent back toward the sun and it managed to keep growing.

I spay these areas over and over on my property to ensure I am not the cause of their spread. I will continue to do my best in controlling Canada thistles in new and existing wildlife properties, but these two top-line weed predators make a thistle look like a dandelion. Wild parsnip and Poison hemlock deserve a lot more attention than does the lowly Canada thistle.

Scott Rall’s Twitter address is @habitatchampion.


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