Weeds have been in the media quite a lot lately. Usually related to some sensational story about “superweeds” and how they’re “winning.” So it was extremely refreshing to read the measured take by Carl Zimmer in the New York Times Environment section, titled “Looking for Ways to Beat the Weeds.” Zimmer doesn’t resort to over-the-top statements and headlines as link-bait, and instead presents an interesting and accurate assessment of many of the problems with weeds. Perhaps most refreshing? He doesn’t even use a glyphosate-resistant weed as his hook. Instead, he uses barnyardgrass, which has not evolved glyphosate-resistance yet, as an example of “a supremely triumphant weed.” He even discusses some of the other interesting traits weeds have evolved over time, including flood resistance, crop mimicry, and prostrate growth habits.
Barnyardgrass, for example, has changed dramatically from its non-weed ancestors. They originally grew on dry land, for example, and were thus poorly suited to the flooded fields where rice grew. The weeds have evolved a tolerance to waterlogged soils.
This is often lost in the discussion of weeds: they will evolve to ANY selection pressure we apply repeatedly. If you mow your lawn, you’ll select for low-growing weeds. If you till the soil annually in the early spring, you’ll select for weeds that emerge later in the year. And yes, if you apply the same herbicides over time, you’ll select for weeds resistant to herbicides. It’s evolution, and it is rather common in weed science. Kudos to Mr. Zimmer for recognizing this, and more importantly, not buying into the hype that superweeds will eat your family.
I encourage you to go read it now.