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Saturday, May 6, 2017

The End of Garlic Mustard?

This year, one of the worst invasives has largely disappeared from some sites.

Is a disease killing it? Will the "loss" be temporary? Can we encourage it?

Withering, discolored leaves on garlic mustard (Alliaria petiolata).
Is this the beginning of the end of a great scourge?
Many state websites call garlic mustard one of the most destructive invasives, degrading the biodiversity of millions of acres.

But this spring, a number of stewards have reported similar experiences:

"I visited three areas where we’ve had major garlic mustard infestations.
In one, I found a few stragglers. In the other two I found none at all.
It’s almost spooky."

"We have definitely had this experience at Deer Grove, but what I saw today is more than the effect of steady pulling.  The odd thing this year is that I am not seeing even the occasional random stem.  I walked miles and miles and saw 3 stems total."

"I had the same experience 2 days ago at Schaumburg Road.  I walked a couple miles through the woods and saw about 10 plants.  The only exception was one 3 acre grove.  Now to figure out the difference between that 3 acre grove and the other 100 acres."

"Your report of the decline of garlic mustard is consistent with my
observations over last 3 or 4 years in NE IL and NW IN. Many sites I visit
have had a dramatic reduction in Gm. Many Gm plants have crinkled leaves
after blooming. I believe a virus is responsible based on how other
species respond to pathogenic viruses.”
For a couple of years, we've noticed a few sickly plants like that at Somme. We decided not to pull them (but to snip off any forming seed). If this is a disease, and if it's not doing any other harm, we wanted it to spread. These results are being found at sites scores of miles distant. At many areas farther away, garlic mustard infestations are still virulent.

Mike Tuttle found some research on viruses attacking garlic mustard:

A number of the comments (below) make interesting suggestions.

There's been some discussion about volunteers moving sick plants to new populations. Is that legal? Probably not. Federal agencies certainly wouldn't do it without doing a lot of very expensive research first. The viruses referenced above also infect some crops (like turnips).

Here's something of a parallel - but in this case with gypsy moths. I once heard that staff folks from one forest preserve went to areas of sick gypsy moths to gather infected caterpillars - and released them in areas the gypsy pests were starting to over-run. I observed one area said to be treated this way. The moths came through in numbers sufficient to attract breeding yellow-billed and black-billed cuckoos. But they did not defoliate whole trees, and the infestation was over after a year or two.

Are there people who are experts at this kind of thing?


  1. The 3 acre grove "found control plot" is definitely worth scrutinizing. Is it in a moist pocket? Does it hold the mist, dew, snow longer than other areas? A visit in the twilight or early dawn might help reveal that, as the fog settles or lifts over the land.

    Are there walnuts or honeysuckle or other soil affectors around? Is that area more mycorrhizal than others? Is it warmer, cooler, more or less wind protected? Is the insect or insect predator life richer? More fungi? What crawls in the soil?

    One possibility is that with the abrupt loss of ash seeds, winter seed eaters are desperately looking for alternative endosperm food. Areas that lacked ash would not see this sudden shift, and in once ash rich areas the impact could be temporarily dramatic.

    Spring lake has grasshoppers that eat the leaves of garlic mustard. Maybe now if the population ends up dropping they could become regulators. If. For anybody up that way still it would be worth a look.

  2. Miami & St Paul Woods also have almost no GM. However, I'm betting that it was the winter weather.
    Kent Fuller

  3. I too suspect weather must be a factor; the thing that puzzles me though is that GM is thriving up here in McHenry County and the weather hasn't been much different up here, as far as I know...minimal snow cover, extremely mild winter here as in Cook...

    1. good observation. The weather is 'triggering' something perhaps; but that triggering depends on a difference in conditions between the affected and unaffected areas. Do you know what the history of ash seeds were in the unaffected areas of McHenry County? Were they areas where the ash has been long-time removed and taken out of ecological-feedback-loop-play?

  4. Perhaps there is a natural, evolutionary-derived decline occurring. Interesting paper summarized here (, full paper here (

    1. That is a fascinating paper. The authors point out that invasions should be in any case managed to prevent damage to the native plant community. The thesis that A. petiolata populations become self selecting for reduced sinigrin which then affects the population viability could explain why a mature population is then susceptible to a pathogen.

  5. Plenty of it up here in southern Wisconsin. I was also in Massachusetts and Connecticut recently and garlic mustard was all over the roadsides. In the last few years I have notice many garlic mustard plants that appear to be spindly with damaged tips. I just assumed it was frost damage given our crazy temperature swings in recent years. I can only pray it's the beginning of something else :-)


  6. I'm also in Southern WI, and we are seeing a small decrease in the garlic mustard on the sites we're managing, but this could be due to annual variation or just all the hard work we've been putting in!

    I've been volunteering doing garlic mustard control work at Blue Mound State Park (we could use some help if anyone is up this way!) There I've noticed a lot of plants with small holes in the leaves. Not sure who is making the holes, and I'm not sure they're having much of an impact on the productivity of the plants, but its something.

    I have an odd but serious request: is there a chance I could come down and harvest a dozen or so typhoid mustards to try to inoculate a couple populations locally, assuming we are talking about a virus, I'd like to help it spread!

    Frank Hassler
    Good Oak Ecological Services

  7. This is exciting, and sounds like a disease.

    Do keep in mind, however, that extensive research on Alliaria throughout the ne US has shown that it is most damaging soon after it arrives at a site ... it's able to kill with high efficiency the mycorrhizal fungi that other species depend on to obtain soil nutrients (esp P). However, in time (decades), the local mycorrhizal fungi adapt, and Alliaria become no more a problem than it is in its native western Europe. What Steve has described here, however, seems a quantum leap above what had observed previously elsewhere.

    WHile we're on Alliaria, did anyone have the experience I had in Madison a few years ago, during our "winterless" winter (2012??)? There was just an explosion of Alliaria, and some plants of tremendous size ... almost as if either two generations packed in one year, or the plants just kept growing to enormous size, with multiple shoot per plant, up to 3 or even 4 feet in height.

  8. Champaign Parks are seeing an explosion of GM along the stream corridors and bike trails. Ash trees and Bush Honeysuckle have been cut by the city and the park people and master naturalists are trying to mop up. Funding for flood control and public safety seems to be available.

  9. Abundant species are a potential resource for other organisms, especially microorganisms. I hoped to promote the evolution of a garlic mustard disease by 1) causing slow death allowing incubation of disease (pulled plants were gathered into bunches as much as a hand could hold and stems were broken at least once), 2) encourage spread (by placing bunches in trees as high as possible), and 3) after diseased plants were observed trying to mix apparently healthy and diseased individuals in the bunches.
    I felt lucky as the system apparently worked. In 2004 I observed garlic mustard with krinkled leaves - most individuals flower but produce no or few seeds as a result of the misshappen leaves. I believe I presented the information on the VSNstewards group- suggesting other stewards might want to come to Cranberry or Spears and collect diseased plants. I remember talking to George Johnson about the disease and I offered to bring diseased individuals to Merwin but Roger Anderson asked me not to because he had an experiment going.
    Garlic mustard is in low abundance at Cranberry but one could not walk 3 miles and see only 3 plants, but they have become a problem of lower importance than dandelions.
    While I believe my encouragement of the evolution of disease worked for Alliaria, I confess I have applied the same ideas to Phalaris and have not seen any evidence of success. Evolutionary management of non-natives does depend on mutations arising that can overcome plant defenses.
    I also believe that much of the success of plants is determined underground by the microorganisms. The presence of the disease is probably not sufficient if the native community cannot control the underground community.
    Dennis Nyberg (I don't know how to change my no longer appropriate blog 'handkle'.)

  10. beaubien woods on the south side of chicago does not have this disease yet, but maybe a plant could sneeze into the wind for us.

    1. Robb, a handful was brought to Beaubien 27 May, but I spent 40 minutes walking around and did not see any garlic mustard.

  11. So where can one go now to collect some diseased plants to spread??

  12. While conducting a spring bird count last Saturday, garlic mustard was very abundant in northern Rock Island County, IL.

  13. Still thriving and spreading like wild fire in Eau Claire and Dunn Counties, WI. So tired of trying to pull it. follows road side mowers and deer trails as well as traveling along flood zones without abatement. I don't care if it is illegal to transport the sickly plants. A few years ago I actually saw someone selling garlic mustard that was in flower as a cut herb at the Madison, WI farmer's market...and he knew he was doing something illegal because when I asked him if it was garlic mustard he quickly hid it. When I try to educate people about garlic mustard they often just don't get it and simply ask if they can eat it. Sick of trying so if you have identified something that may help best to figure it out ASAP!

  14. I'm in southern Wisconsin, and recently visited two island sites on a river system. Island 1 is completely surrounded by water. On Island 1 the understory is filled with cut-leaved toothwort and mayapple with pockets of wild ginger. But mostly, the herbaceous layer is dominated by garlic mustard, and there's a dense seedling layer throughout the site.

    On Island 2, there is an access road across the river, which a farmer, hunters, and apparently deer use. On Island 2, the fringe of the island is dominated by GM where it floods frequently, but beyond that the understory is a rich mix of toothwort, wild leek, mayapple, geranium, and trout lily.

    I'm unsure what caused the infestation on Island 1 versus the excellent condition of Island 2, which is more disturbed and more frequently visited.

    I've been seeing holes in GM leaves but with no apparent damage to the plant throughout the region.

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  16. Here in Fox River Grove, IL, at the intersection of Lake and McHenry Counties garlic mustard in just one year has almost completely vanished. A year ago it blanketed degraded woods with flowering plants. Now it is hard to find even a few first year plants and the ones I found are smaller than usual. I only found a single, small stand of flowering garlic mustard.

    Another theory on the demise of garlic mustard from the University of Illinois is here-

  17. Pull the survivors up by the roots! Don't allow natural selection any chance to work.

  18. To Anonymous - June 2.
    The reason I'm not worried about my decapitated mustards contributing to natural selection is that they are biennials. That is, they die after their second year. So, if they don't produce seed, all the foliage is doing is providing food for the disease we hope will stick around, evolve itself, and continue to spread.

  19. Now if the same would happen to sweet clover...