Admirable, Abundant, and Adaptable, But Not Aggressive

During the last month or so, I’ve had several people tell me how aggressive marestail (horseweed, aka Conyza canadensis) is, and how this is a particularly bad year for it.  One person suggested marestail should be added to Nebraska’s noxious weed list.  This week, Olivia and I drove from our Platte River Prairies to the Niobrara Valley Preserve – right through the center of our state – and I tried to document what is certainly a summer of abundance for marestail.

Marestail is an annual/biennial plant with tiny flowers and fluffy wind-blown seeds. Marestail is abundant across much of Nebraska this year, including in this flat area at The Nature Conservancy’s Niobrara Valley Preserve.

Here are a few things you should know about marestail right off the bat.  First, it is native to Nebraska and most of North America.  It acts as an annual plant in states to the east of us, but acts as a biennial here, usually germinating in the fall and blooming the following summer.  In its native habitats (including grasslands), marestail is a colonizer of bare ground, filling spaces between plants left open by disturbances like grazing, trampling, animal burrowing, drought, or fire.  Because marestail loves open soil conditions, it isn’t surprising that it has become a weed in crop fields.  It has garnered special attention lately because it has a strong ability to become resistant to herbicides, including glyphosate, which it started showing resistance to way back in 2006.

In other words, marestail is a tough native plant that has always scraped out a living when and where it can.  However, it’s not a plant that can push other plants around.  Instead, it sits in the soil (as a seed) and waits for a time when surrounding plants are weakened and abundant light is hitting the soil.  Then it pops out of the ground and tries to grow, bloom, and produce as many seeds as it can during its short window of opportunity.  In any particular year, marestail can be found here and there in most Nebraska prairies, especially those in the western 2/3 of the state.  However, it also seems periodically to respond to certain weather patterns and exhibit a flush of abundance across a larger region – as it is doing this year.  Many short-lived plants do the same thing, each with its own individual preferences for weather patterns.  Many Nebraskans might remember the huge sunflower party across the Sandhills back in 2013, for example, following the big drought of 2012.

During late summer, marestail flowers and produces seed heads, helping it stand out from the surrounding vegetation.

Whether it’s sunflowers or marestail, huge regional flushes in abundance don’t last long.  By 2014, annual sunflower numbers in the Sandhills had returned to normal – patches of yellow flowers here and there, around livestock tanks and fence corners, and wherever else there was open soil to grow in.  Marestail will do the same thing in 2019.  That pattern of boom and bust is not evidence of an invasive plant.  Instead it characterizes a plant that is too weak to compete most of the time and has to take ultimate advantage of the few windows of opportunity it gets.  When it is abundant, marestail isn’t stealing resources from other plants, it is taking resources that weren’t being used.  I don’t know for sure what weather patterns led to rampant marestail germination last fall, but I’m sure this year’s abundant rains have played a big role in the survival of a large percentage of those seedlings.

Call me crazy, but I think marestail adds an attractive texture to the grassland this year.

When short-lived plants like marestail and sunflower (along with ragweed, gumweed, and many more) are in the middle of a short-term explosion in your prairie, you could choose to fight them.  You could, for example, mow them off, trying to prevent them from making seed.  However, that’s a lot of work, and the plants will do everything they can to regrow and still produce seed – it’s what they do, and they only get one year to do it.  Even if you do keep them from going to seed, there are many thousands of seed already in the soil, ready to spawn the next generation of plants whenever they get the chance.  You could also spray short-lived opportunistic plants with herbicide, but I wouldn’t recommend it.  First, you’ll likely kill the surrounding plants (the ones that normally out-compete marestail and sunflower) and just trigger another explosion of opportunistic plants the f0llowing year.  Second, with most short-lived plants, by the time they’re big enough that you notice them (especially by the time they’re flowering) herbicide treatments just make them produce seed more quickly, so are counterproductive.

Marestail might not have big showy flowers, but it can still be an attractive part of a landscape, especially if you know it isn’t dangerous.  If you’re still not a fan after reading this, just squint your eyes and pretend it’s a funny-looking grass.

The smartest choice is to just sit back and marvel at these periodic phenemona, knowing you’re watching a short-term and harmless event.  Marestail, of course, doesn’t have the wide aesthetic appeal of sunflowers (though not everyone likes sunflowers either), but it has its own distinctive charm.  I think it adds an attractive texture to the landscape, but I’ll admit I’m a little odd.  Regardless of whether you find it attractive or not, it’s here, and it’ll be here whether you like it or not.

Fighting back against these periodic flushes of marestail and other opportunists is expensive and futile, and usually results in weakening the plant community that normally keeps them in check.  Most importantly, remember that, at least in grasslands, marestail doesn’t steal resources from the plants you like, it just takes what they can’t use.  What’s to dislike about that?

30 thoughts on “Admirable, Abundant, and Adaptable, But Not Aggressive

  1. Hello Chris

    We are having an explosion of marestail here in Illinois as well. There are more plants and it is taller than I have ever seen it.

    Thanks for the article.


  2. We see it in disturbed areas a lot. I haven’t had the time to observe its use by birds etc. Does anyone have some information? While it’s not something I’m likely to plant in the garden, if it’s something which provides value in a landscape, we should know about it.

  3. Wonderful, perceptive take on native ‘weeds’. One could add the importance of holding the soil in place during periods of prolonged drought or bison disturbance

  4. Converted an ag field this year to a bare root-tree planting (CRP). On 8′ x 8′ centers. We put pre-emergent herbicide in a band around the trees, but left spaces in between alone. Horseweed filled in the gap, almost to the exclusion of other plants. 6-7′ tall, and yet not densely underneath and it was quite easily to walk through it (unless sections with giant foxtail). I even hope that it partially hides some of the juicy oaks from the deer (one can always wish at least). I’d take horseweed (and common ragweed) over the smartweeds and foxtails in this instance.

    • We just did the same, converting 10 acres of cropland to bare root seedlings. Marestail is taking over and I’m not sure what if anything I should do. How did your seedlings end up?

  5. I know Marestail is immune to Roundup in Monroe county Il. and Franklin County Mo so its definetly more visible these days.

  6. Thank you, Chris! This article has been so informative and helpful. I’ll be happy to squint my eyes and think mares tail is pretty, as long as I know it’s not invasive and going to take over all the hard work of establishing our pollinator acres.
    New request- what can you tell us about prickly lettuce? More invasive?

    • Hi Patricia, In my experience with prickly lettuce, it is another opportunist species, and not invasive, but that experience is pretty limited. The only times I’ve seen it in big numbers have been in early stages of our prairie restorations, and it didn’t persist for more than a year or two.

  7. This really was a helpful article. I’ve been confused by increasing references I hear to “invasive” plants, when the plants in question actually are native, and don’t seem to be doing anything except being enthusiastic growers.

  8. Great perspective Chris. We’re seeing more of it here in NE Colorado this year too and many of the neighbors to our natural areas keep complaining about the proliferation of “weeds”. I’d much rather have marestail than puncturevine or cheat grass in those disturbed areas.

  9. Thanks for giving us your perspective, Chris. It’s a reminder not to jump to conclusions and immediately be judgmental. Horseweed certainly doesn’t rank at the top of my favorites list, but I did know it’s native in Michigan, too, and it must play some role, even if it’s an unrecognized one.

  10. Then apparently native to eastern SD as well; I had not seen it until early 2000’s an assumed it was introduced. Here in Western Montana(very dry moisture regime-10-12″ annually) we had an influx of native Six Weeks Fescue and Woolly Plantain due to a wet June, 2018. Like them both better than cheatgrass!

  11. I removed weedy sod from my back yard in Minnesota (Twin Cities) last fall and frost-seeded a pollinator mix from Prairie Moon in Winona, MN. This spring, after a massive April snowstorm and a wet spring, I had two of these, taller than anything else when I mowed the plot for the first time in July (a few weeks later than I should have…oops.) I could not ID the plant at the time, but now I recognize it.

    Thanks so much for the blog. I read about it in the Minneapolis Star Tribune earlier this year and it’s fast become one of my favorite emails.

  12. This grows in the area across the street where the neighbors allow me to garden. It’s quite the hodge podge, and not quite enough light to grow many vegetables, but we get a few things out of there. Plus, there is a black walnut tree on the west side of it. I usually pull out whatever marestail I come across, but I sometimes get behind and some go ahead and bloom. I won’t be as concerned about them now.

  13. Good topic. I have it on my property near Chicago and it’s a very beautiful plant, unique and attractive. It is easily removed from areas if someone chooses to do so by pulling, but its aesthetic appeal is high. I think if people stop automatically jumping in their minds to the preset of “weed!!” they could enjoy many more of our native plants and flowers.

  14. Different perspective about Marestail:
    If you are an advocate in the east for pocket meadows or pollinator gardens in suburbia, it’s a problem.
    It is aggressive, crowds out preferred better blooms. And even if broken off three times during the season it will produce abundant seed heads where you don’t wont them.
    I wonder how it fits into sowing attempts or restoration of natives in Nebraska?


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