The story of a deceptive killer …
… in which a seemingly-irresistible force meets a few possibly-unstoppable stewards.
It’s a drama. Who will win?
The poisonous killer plant in question is Convalaria majalis. As a deceptively favorite garden plant, it’s called lily-of-the-valley. But stewards of biodiversity call it the death lily, because – under certain conditions in nature – it kills all.
The photo below shows what this monster looks like – toward the edge of the patch, where some diverse vegetation still survives. In the middle of the patch, we found nothing beside death lily and dirt.
But the next photo zooms in to show why this spot is worth caring about:
Above, you see a purple-leaved plant on the Endangered list – cream vetchling or wood pea (Lathyrus ochroleucus). It deserves life, and, indeed, reproduction and recovery of its once-common woodland status. (Notice the huge stipules visible where one compound leaf meets the main stem. These stipules distinguish the wood pea from some related look-alikes.) This plant, which now survives in few other places in Illinois, inspires the work shown in the next photo, of the same place, but after some handiwork.
Here six stalks of wood pea and a bit of other vegetation stand separated from the lilies. Step one - accomplished. Next we step way back, and you can see how big this patch is:
We're looking from the north. The south edge of the patch isn’t quite visible here, but if you look closely, you can make out three of the Restore Moraine team, weeding this menace from rare species on that south edge, at the top of the slope where the patch ends.
These are the heroes yanking out stems that are near the higher quality vegetation. We want to save as much rare vegetation as we can. Stewards from left to right are Eriko, Ryan, Mary, Mills, and Erica.
Then comes step two!
The herbicide glyphosate kills all plants. It’s a last resort for species like this lily that aren’t killed by something less toxic.
Here the heroes are Ali, Jordan, and Steve. Ali and Jordan are spraying death lily. But remember this photo?
Not so for the death lily. This whole lily colony is one plant, roots connected underground. What will happen to the roots in the area where we pulled out the leafy stems – when we spray the nearby intact vegetation? We don’t know. Has anyone else done this? We expect, from experience with other invasives, that the remains of un-herbicided roots will put up new stems near the endangered wood pea and other surviving natural vegetation. We may continue to pull the weakened new shoots, or perhaps we’ll carefully hand-wipe them with herbicide.
In the meantime, we’ll also focus on the rest of our priorities here.
The intrepid Restore Moraine volunteers work in only perhaps 20 acres of the 2,200-acre Moraine Hills State Park. Indeed, within these 20 acres, most of our work has been directed toward a top-priority four acres of rare high-quality oak woodland. Quality areas have shrunken under the stresses of past grazing, invasive species, over-populated deer, and excess shade from lack of fire. The four best quality acres are divided up among five little slopes where the ecosystem has somehow miraculously survived.
As described by Dr. Wayne Schennum, who studied it for decades, what survives here contains patches of rare high-quality remnant white and bur oak community – not recognized until relatively recently as a high priority for biodiversity conservation. Like the vast prairie, oak woodlands were once a major natural feature of this state. The park also has bogs and fens and sedge meadows and prairie remnants. It has many rare animal populations that also deserve stewardship. We help some with them, but we mostly try to focus on restoring health to this oak woodland.
Dr. Schennum, long advocated for “first aid” rescue work for this woodland, mostly by cutting invasive trees. Species had been vanishing in the gloom, as he documented. The diverse animals and plants of oak woodlands thrive in dappled sunlight under oaks naturally well-spaced by fire.
Friends of Illinois Nature Preserves agreed with DNR biologist Melissa Grycan that this site should be a priority. With her guidance and support, since June 7, 2025, the resulting Restore Moraine stewards have worked every Saturday morning, year round, to do what oak woodlands are increasingly understood to need.
We hadn't tackled the death lily until last week. We've studied the literature and the Internet and asked expert stewards about their experiences. This menace is most vulnerable to herbicide in spring. No other approach controls it, except repeated hand pulling, which is impractical for large populations. We hope to hear from others about varied approaches. This post will be updated as we learn more.
Endnote
At Moraine there have been surprises. We’ve found many new populations of Endangered or rare species. All have been injured by excess shade or invasive species. Hundreds of acres of ailing oak woods here need more care. They need regular fire, invasives control, tree thinning, and seeds – which need to be hunted, gathered, prepped, and broadcast into areas where richness has been lost.
But Moraine isn't the only Preserve with a lack of resources. Most Preserves are suffering. We can't just shift resources here from elsewhere. The Illinois Nature Preserves System needs more staff, contract stewardship, and support for volunteers. But with high-quality woodlands even rarer than prairies, some of us decided that this Nature Preserve was a priority for help by a Friends volunteer community. We're less than a year old here, but off and running. All are invited to come and help, if you're so moved.
Acknowledgements
Thanks for review, suggestions, and editing to Lana Federer and Jonathan Sabbath.
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