To Kill a Monarch

Not exactly a Harper Lee title, nor is this a story about the run up to the first World War (Archduke Franz Ferdinand was, strictly speaking, not yet a Monarch… human or butterfly). And as we shall soon see, no monarchs were actually killed in this episode, tough some habitat was deliberately destroyed.

Specialists, are they truly special? Word play aside, anyone whose diet is limited to a very short list of possible foods starts out at a disadvantage to another whose opportunities for food are less restricted – particularly when the supply of their particular food source comes under pressure. We humans not only don’t eat milkweeds1, we find them a nuisance in fields where we would prefer another plant species.

Yesterday found me at the wheel of a spray rig, applying herbicide to kill weeds in a soybean field. Hundreds of millions of acres throughout the US Midwest have similarly been dosed these last couple months as the 2019 cropping season limps along. There is still a fair amount of land not “under the plow” (quotes because plow is more euphemism now than was once the case) … and this non-agricultural land can still host milkweeds and thus monarchs. Monarch habitat loss due to agricultural weed control – though a significant concern – is slowing2. And efforts are underway to deliberately increase the milkweed presence in the US Midwest.

Earlier this month Jeff Ollerton blogged about visiting the U.S. and working on a survey of milkweed family members and their distribution on the Eastern Seaboard3. His post came to mind as I was spraying, and I noticed a common milkweed just ahead of me. We also have hemp dogbane (Apocynum cannabinum) on the farm where I work, though I didn’t have one handy to photograph yesterday. The pictures here are of three weeds we struggle to control here – all three photos taken within a few meters of each other. The milkweed (Asclepias syriaca) captures the most attention for a general audience due to its role as monarch habitat. Canada thistle (Cirsium arvense) and marestail (Erigeron canadensis)  capture more attention from farmers here as they are more difficult to control.

Three perennials at Woodstock

Left to right, 3 weeds common in central Ohio soybean fields:  Common milkweed; Canada thistle; Marestail

In a few days I should be able to see whether any of the plants pictured here is still alive. If I had to guess any might make it my money would be on the thistle. If one looks closely at the thistle picture there in the middle, you might see a very small thistle plant in one corner. That one likely is dead. The two shoots in the center are likely not seedlings but regrowth from an older rhizome – something the chemicals I was using will have a tougher time killing. The foliage in the photo will likely burn up, but the rhizome(s) may well send up another shoot later this summer.

For anyone concerned about this catastrophic loss of plant material in a small Midwestern soybean field, you may rest assured there is still plenty of monarch habitat on this landscape.  Within a couple hundred meters of where these photos were taken there is a drainage ditch.  For a bit over ten meters on either side of that ditch there is undisturbed soil supporting all sorts of fauna and flora.  Indeed there are so many representatives of each of these three rascals to provide seed for all future soybean field efforts.  The monarchs needn’t worry.

  1. Though we don’t eat milkweeds it seems there may be a market for fibers from milkweed:
  2. Good backgrounder on crop production in the US heartland and how milkweeds as habitat have fared in recent times:
  3. Jeff Ollerton visits the U.S. and studies monarchs and the milkweed family:


  1. Poison? Sure that’s a nuisance and all, but the real problem with eating milkweeds is that at a certain point your mouth becomes glued shut. Which for some people, is a definite step forward in life.

    A little known fact is that Bob Dylan is the only person capable of writing a song that involves rhyming Asclepiadaceae–I wouldn’t try it if I were you.

    On the chemical theme, I have a new chemistry book review post out, but I wouldn’t waste much time on that either. I sure didn’t.


    1. Jim!!
      It’s been too long. Was beginning to think something horrible had happened – like your being caught in a serious CA forest fire.
      You’ve reminded me of something we used to toss around in statistics class back in the day. Back from a soybean yield trial plot where we’d sprayed herbicides for weed control… when asked what we’d been up to we could offer “Just a little Poisson distribution”. Let Mr. Dylan riff on that.

      A new chem book? Have been waiting for someone to update Charles’ Law, for I’m sure the pressure to do so must be getting intense.


      1. Yes it has Clem. And something(s) did, and still are, but I won’t go into them here.

        I suggest never engaging a Frenchman on the expected number of fish per unit sampling effort. I can proudly say I never have, and it’s turned out well. Also, Bob Dylan has a song in which fish trucks and explosions are mentioned in the same phrase…but you knew that already.

        Liked by 1 person

  2. […] might recall, from a couple posts back, how I don’t spare the milkweeds when preparing fields for planting on this landscape.  In […]


  3. […] get used to them, deal with them as necessary, and move on. Milkweed (Asclepias syriaca) has been mentioned here before. Killing milkweed plants in a cropped field and shaking the fist at those along the ditch which go […]


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