Central Virginia Organic Gardener

"And 'tis my faith that every flower enjoys the air it breathes." - William Wordsworth, 1798

Sunday, March 11, 2012

It's happened: a superweed has been created

It has happened: overuse of an herbicide has lead to the development of super weeds. This development has been expected for years. Here's the deal: weeds are tough, adaptable plants. If you spray them with a targeted herbicide, almost all of them die...except for the few survivors who are able to resist the herbicide. If these plants survive to reproduce, they pass their protective genes on to their descendants and ...voila...in a few generations, all the plants are resistant and that genetic variation spreads. This is the same process that happens with bacteria and antibiotics, but that is even more scary, as bacteria can, under some circumstances, swap gene inside a host organism (so the process can be accelerated).

The actors here are Palmer amaranth (aka pigweed) in cotton fields in Georgia and glyophosate herbicide (trade name: Roundup). These cotton seeds have been genetically engineered to resist the effects of glyphosate, so they can be heavily sprayed with the stuff (imagine the environmental consequences, especially to aquatic organisms which are very vulnerable to this stuff and get a good dose from agricultural runoff). Pigweed grows fast and severely limits cotton yields. Farmers are resorting to old methods, like hand pulling, to remove this resistant pigweed, which, if left to set seed, can produce close to a million seeds per plant!

What I find interesting in the NPR report below is the weed expert's recommendation that cotton farmers use a tried and true organic method to deal with pigweed, that is, plant a cover crop of rye and intersperse cotton plants in it (though this method has not been fully worked out for large scale use, according to this expert). Pigweed cannot really grow in a rye field, and the rye also prevents erosion and adds nutrients to the soil when plowed under after the cotton harvest. What do Dow and Monsanto propose? More genetically engineered cotton plants that resist heavy doses of other herbicides. Can a multi-herbicide resistant pigweed be far behind? And more environmental damage? Other sad news is that pigweed is just one example of an herbicide-resistant weed currently posing a challenge to all growers.

For the NPR report, go to:

Palmer amaranth photo credit: Univ. Missouri Agricultural Extension office, at:

And, if you live in Georgia, continue to hand pull any pigweed you find in your yard and garden. I've heard that, when young, it is edible (but research this before you do and only eat organic weeds!!!!)!
Happy(?) gardening? How about "environmentally conscious gardening" this week!


Carolyn said...

Just the mention of Monsanto sent a shiver through me. Such a scary concept, and yet few of us will ever learn.

Judy Thomas said...

Hi Carolyn,
I was born an optimist, but I often worry about the hubris of humans as we go down this destructive path, blithely believing nature will take all these insults against it without biting back.

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