Crown Vetch - How to Combat an Evil

It's a threat to biodiversity. This menace can roll over a fine, ancient prairie or savanna, killing all - rare plants and animals alike. It's a bad plant! Really? Can a plant be "bad"? See Endnote 1. 

With its colorful but deeply ugly face, it glares at us, below:

A nightmare? But this is a story with a happy ending. We found the feared and hated killer invasive in a high quality area - near endangered species. We'll show what we did to wipe it out. But first we'll say why.

The photo above is a detail from Palatine Prairie where it was left to expand for many years. In large parts of this original prairie, as shown above, crown vetch had wiped out nearly every other plant and animal. Aside from couple of sprigs of toadflax (white flowers) and a few blades of sedge, nothing else survives.

In another photo from nearby, a few more plants survive. In the upper left corner are some blazing star and prairie dock leaves, but the trauma is shocking. Perhaps twenty plant species that would have been in this photo a few years ago are already gone, and vastly more species of invertebrates.

So what did we do (as photographed below) at Somme? After much experimentation, we've adopted a radical approach. In high quality areas, we cut most other vegetation, to save it - and get it out of the way temporarily. Think of a prairie fire in summer. Everything above ground is removed, and the prairie sprouts right back.

Here's what the patch looked like when we finished cutting away the rare beauty. Next step: we spray with Transline, a herbicide that kills mostly legumes (like crown vetch and prairie clover) and composites (like blazing stars and asters). So we especially carefully cut all the natural legumes and composites, and we also cut any other vegetation likely to get in the way of the spray. We want to coat every crown vetch leaf with that medicinal chemical. 

Next, step back for a minute to think about the context. The cut patch is in the middle with mostly prairie vegetation in the foreground and savanna vegetation near those trees. Literally hundreds of plant species here are threatened.

The open savanna or "prairie" vegetation here includes prairie lily, both white and purple prairie clovers, prairie violet, and scores more conservative plants.

The next act was to spray:

The blue is a dye in the Transline herbicide. We can see it coating every leaf. We did not successfully cut out every other plant, but we cut most of them. The bergamot and violets we see here will probably survive fine. If not they'll spread back in from around the edges. We cut them, to some degree, to save them. But we cut mostly to make sure we killed all the crown vetch.

Too many times, we had returned to a sprayed patch, years later, to find that we'd missed a bit, and the infestation was again virulent. (This approach is too demanding for larger populations, but even there, it may be helpful to use this sort of approach to save some patches of highest quality vegetation so that it and its soil biota can recolonize.)

Here, steward Eriko Kojima uses a backpack sprayer. For small patches, she often uses a little hand sprayer. 

She has done this work in very high-quality prairie ("Grade A") with complete, permanent control of the vetch, and no loss of high-quality prairie plants. For years, we repeatedly checked that spot. The crown vetch was completely gone. There was no noticeable difference between the sprayed patch of high quality prairie and the unsprayed high quality prairie all around it. 

On the other hand, we also know from experience that older patches of the vetch have years' worth of seed lying in the ground, waiting. They sprout. We watch for them and kill these smaller, isolated plants before they have time to booby trap the ground with more seed. After a few years, all but the worst populations are gone. The lesson: find it and zap it early.

This post is and update and expansion of a section of a previous post.

It would be good to hear from others about successful and unsuccessful approaches.  

Endnote 1

Biodiversity loss is a major threat to the planet. There are other evils: climate change, war, oppression of some people by others. Not all of us need to take time out of our happy lives to work hard to end all evils. But it's a badge of honor to humanity that many of us do pitch in where we can. Biodiversity is an incomparably important heritage that has evolved over hundreds of millions of years. Our species is unintentionally wiping out major parts of it. Numerically, most species and ecosystem types are threatened with oblivion or radical depauperization. 50% of the rainforest is gone. 99.99% of the original tallgrass prairie is gone. Less than that survives of high-quality oak ecosystems. Invasive species are today one of the two or three major threats to most surviving remnants. Many of us have been inspired by the words and actions of Rachel Carson, Aldo Leopold, Robert Betz, Tom Vanderpoel and many. Also, of course, there's this quote: The only thing necessary for the triumph of evil is for good people to do nothing.