The Local Disappearance of Garlic Mustard

Jim Steffen —  May 26, 2017 — 15 Comments

When it comes to controlling invasive plants, a little faith can’t hurt. This is particularly true for garlic mustard (Alliaria petiolata).

We have been struggling to get this highly invasive biennial plant under control at the Chicago Botanic Garden for more than 20 years. When I first began working on restoration of our 100-acre Mary Mix McDonald Woods, it took weeks of hand-pulling with many volunteers each spring to clear just 10 or 11 acres. After years of not letting the garlic mustard set seed in the McDonald Woods, a few years ago we finally began to see a light at the end of the tunnel (though we’d still end up with mountains of pulled garlic mustard each year). Thanks to the tremendous help of Garden volunteers, garlic mustard growth in the Woods has finally been curtailed, and each year we are now able to remove all flowering garlic mustard in the Woods’ entire 100 acres.

Garden volunteers pose with a pile of removed garlic mustard at an annual "garlic mustard pull" event.

Over nearly two decades, Garden volunteers have played a critical role in helping remove garlic mustard from the McDonald Woods.

About six or seven years ago, we began a new ecological restoration project in the Barbara Brown Nature Reserve (located at the south end of the Garden near Dundee Road). The area was highly degraded and choked with buckthorn shrubs (Rhamnus cathartica). After the buckthorn was removed, the following spring was a nightmare in terms of garlic mustard. Acres upon acres of garlic mustard monoculture required removing several dump truck loads just to begin making a dent in the population.

Garlic mustard takes over after buckthorn is removed from the woods.

After buckthorn was removed from the Barbara Brown Nature Reserve, garlic mustard plants completely dominated the understory vegetation for several years.

Garlic mustard became so dense in the Brown Nature Reserve that we were reluctant to pull it, since the resulting soil disturbance would greatly enhance sprouting of the soil’s dormant garlic mustard seeds. Fortunately, one of the Garden’s creative mechanics devised a basket system on a hand-held scythe. This ingenious tool allows us to harvest the plant tops by cutting and collecting the unripe seedpods—but unlike hand-pulling, using this tool completely eliminates soil disturbance.

Although the Reserve covers only six acres, in the first few years we were not able to remove all the garlic mustard plants before they began to drop their seed. This led to several more years of hand-harvesting to get the population more under control. Fast forward to spring 2017, and we’ve only found about 75 flowering plants to remove so far. What was once viewed as an impossible goal to achieve (i.e., near-total elimination of flowering garlic mustard from the reserve) has actually happened! Too good to be true, perhaps?

A handmade garlic mustard "rake" captures unripe seed heads.

This ingenious device fabricated by one of the Garden’s maintenance mechanics allows us to capture the garlic mustard’s unripe seedheads cut by the scythe’s sharp blade (the curved metal piece along the bottom).

Even with faith as small as a mustard seed, then you can move mountains: nothing will be impossible ― Viola ShipmanThe Charm Bracelet

There have been recent field observations circulating in the Chicago region regarding a possible disease that apparently is having a significant negative effect on garlic mustard (see woodsandprairie.blogspot.com).

Over the past several weeks, observers have reported an almost complete absence of garlic mustard in areas that are undergoing habitat restoration—and this absence has even been observed in areas where no invasive species management has been done. Further, some restoration workers have reported garlic mustard with very “weird” rhizomes that have many small plants emerging along them. This is not at all a normal growth form for garlic mustard. The speculation is that a virus or some other pathogen is deforming and/or killing the plants. This potential pathogen might explain why we have observed such an incredible decline of garlic mustard at the Barbara Brown Nature Reserve this spring.

I have also taken note of several roadside areas along my commute to work that in past years had dense stands of garlic mustard. This spring, I’m not seeing any garlic mustard flowers there at all. Yet quite interestingly, I’m still seeing dense stands this spring in areas outside the Chicago area. What’s going on with our region’s garlic mustard?!

The next few weeks offer a great opportunity for Garden members to check their yards and other nearby areas that in previous years had shown dense stands of flowering garlic mustard. Maybe you’ll see a dramatic decline as well. Since this seems to be a very recent phenomenon, natural resource managers will need to continue monitoring to see if the decline persists.

Wouldn’t it be great if nature offers a way to rid our region of an invasive plant that has been plaguing our natural areas for so long? Stay tuned!


©2017 Chicago Botanic Garden and my.chicagobotanic.org

Jim Steffen

Posts

As a specialist in oak woodland flora and fauna, my goal is to restore McDonald Woods, a 100-acre oak woodland complex, using a number of methods. Through the removal of invasive species, the collection and sowing of seeds from appropriate local native species, the maintenance of nursery populations for seed production, the monitoring of floral and faunal populations and the use of controlled burning, I am striving to increase species diversity and develop a healthier functioning ecosystem. Utilizing my ornithological background, I maintain bird-nesting structures throughout the Chicago Botanic Garden, use bird bands to mark selected species of breeding birds at the Garden, and oversee a cumulative bird list.

15 responses to The Local Disappearance of Garlic Mustard

  1. Wow! When you figure out what is going on in Chicago, make sure you let us know. I moved from the Chicago area to Connecticut and I’m attempting to salvage 6 acres of my own and return them to their pre-mustard garlic state. It is rough going. So glad to hear that CBG has conquered it! Can you post directions for making the scythe? Also, the thought here is that if you weed-whack them just as they start to bloom, they won’t set seed and will just die. Did you ever try that? Will you be studying the anomaly/virus?

    • Hello Jane:

      My experience is that if you cut the plants while they are flowering, they will re-flower and still produce seed. Mostly, we pull flowering plants and remove them from the woods. I have seen flowering plants that were pulled and left in the woods during rainy weather and they continued to grow and develop seed pods. If I decide to cut plants, I wait until the green seed pods develop and the plants are completely done flowering, then I cut them and remove them from the site. The green seed pods will continue to develop it left in the woodland.

      JS

  2. It would be so great to identify the anonymous maintenance mechanic by name. I feel the folks who do all the behind the scenes prep, planting and maintenance in hot weather and cold get almost no recognition for their hard work. There are so many plaques recognizing donors all over the place in the garden, that some amount of visible gratitude for staff would not go amiss. Particularly in this “let them eat cake” era ……

  3. The weird behavior of garlic mustard may have something to do with the presence of the invasive jumping worms (Amynthas spp.) from Asia, which are spreading on the North Shore. These worms change the soil structure and soil chemistry, sequestering nitrate and making the soil more alkaline, changing the composition of the bacterial population, depleting mycrorryzae etc., and their effects on individual plants are mostly unknown (woodland ephemerals will decline as the worms eat the duff layer). Perhaps something in the worm castings repels garlic mustard? Perhaps the earthworms eat their seeds?

    • Hello Martha:

      You are right to be concerned about jumping worms. They can have devastating impacts on the soil and leaf litter. However, as it relates to garlic mustard, we do not have jumping worms, yet, in our woodland. So I do not think they are a factor for us. I would also mention that all of the earthworms we have in Northeastern Illinois are exotic species that tremendously disrupt the functioning of our natural ecosystem. We have studied them for a number of years, even when garlic mustard was growing abundantly, seemingly without affect on the mustard. The jumping worms have arrived at the Botanic Garden, but so far they have not spread to our woodland.

      JS

  4. I am so happy for you. I have just a small piece of property on a ravine and struggle with garlic mustard every year.
    To Jane: In your comment about weed whacking, it is my understanding that even if you cut all the flowers off, they will still go to seed. So unless you rake up all the cuttings from the weed-whacking you will still have a problem.

  5. Ellen –

    That’s what I thought too, but here’s a what I got from the Forest Invasive Plants Resource Center:
    (https://www.na.fs.fed.us/spfo/invasiveplants/factsheets/pdf/garlic-mustard.pdf)

    It does say that it is “best” to pick them all up and bag them after cutting. I’m wondering if CBG has ever tried this. I’m curious about whether they really do set seed if you cut them down early enough.

    “Cutting second-year plants close to the ground by hand
    or with a weed whip may be effective, depending on
    timing and weather. Cutting too early in the season
    will result in resprouts, cutting too late will allow the
    seed pods to mature. For best results, cut just as
    flowering begins. Resprouting will be reduced because
    plants will have used up most of their energy reserves
    producing flowers and seedpods. Try to revisit the site
    to look for plants that were missed. Note: Some
    flowering plants are tiny, only a couple of inches tall and easily overlooked. These plants may
    have only one or two flowers, but still will produce a set of seeds!

    After pulling or cutting, it is best to bag and remove all flowering plants. Depending on weather
    conditions, uprooted and cut plants will continue to develop and may set seed, especially later in
    the season as seedpods mature. For small populations, plants can be decapitated and just the
    flowering tops bagged and removed. Garlic mustard should not be composted, because seeds are
    likely to remain viable. Bagged plants can be landfilled, or dried out and burned. In large
    patches where removal is not possible, pile stems in the most densely-infested area, where the
    seed bank is already presumed great. This, at least, will prevent another crop of seeds from
    being deposited in the forest. Covering with black plastic will help limit the ripening and spread
    of seed from the pile.

  6. Years ago Jim S. told me it would take 6 to 7 years of pulling to eliminate it. I think it took over 10 years. I have not seen one plant this spring. The bad news is that fields of lesser celedane and dames rocket replaced the mustard.

    Art A.

    • Wendy walcott May 30, 2017 at 2:11 pm

      The key is to introduce or encourage replacement species. At the Schlitz Audubon nature center, we saw woodland goldenrod take over , more each year as we attended to certain areas on our path down the bluff. Jewel weed will also dominate garlic mustard. If given the chance.. disturbed soil will yield weeds forever if replacement is not offered. Wendy Walcott, land manager, SANC, retired.

      • Hi Wendy:

        You introduce an important point. Removing garlic mustard without also providing competition, if none exists is very important. One of the reasons we decided to cut the unripe seed heads in the Reserve is that we had seeded the entire area with native species. It was only after controlling invasives for two years and seeding native species that the garlic mustard seemed to emerge from nowhere. By cutting the unripe seed heads, we did not tear the newly established natives out of the ground or disturb the soil.

        Jim

  7. Does this creative, inventive mechanic have a name?? I suspect if the device had been invented by someone on senior staff, that person’s name would have been stated. This feels very disrespectful to those who do much of the hardest work at the Garden. You can do better.

    • Hello Sandy (and others):

      The “garlic-mustard-harvesting scythe” was an idea of mine that I thought would be useful for tackling the garlic mustard in our woodlands, particularly the Barbara Brown Nature Reserve. Riley Obenchain, one of the Garden’s talented mechanics, helped me bring this idea to life. I have collaborated with Riley on a number of projects over the years. I’ll come-up with an idea for a tool that could help us better manage our natural areas, and then bring Riley that concept along with some bits and pieces of material. Using Riley’s sharp mechanical mind along with additional materials that he might dig up from his shop, together we create a new and useful tool.

  8. Carolyn Pearson May 31, 2017 at 8:15 am

    Jim, What an amazing story of 20 years of tenacity, perseverance and ingenuity. Nightmare indeed! I live next to undeveloped park district property and will have to quit whining now about the comparatively few unwanted specimens I find in my yard and garden each year. (As an aside, your mustard seed quote was familiar but recognized from a different earlier source – Matthew 17:20). What a inspirational saga! Well done.

Leave a Reply

Text formatting is available via select HTML. <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

*