The Problem of Herbicide Resistance

Farmers who are growing herbicide resistant crops such as corn or soy may start to identify with Audrey Jr. in Little Shop of Horrors. In that film, later made into a Broadway musical, a dorky florist’s assistant cultivates a plant he names Audrey Jr. after the co-worker he pines for. This is no ordinary plant, this one craves blood to grow and its constant cry to “feed me” wreaks havoc with human lives. While there are no plants that suck blood, although ones like the Venus fly trap do dine on insects, there are ones which at least figuratively suck farmers’ blood. We are talking about weeds that can no longer be killed by herbicides. Weeds along with insects are farmers’ great enemies. They compete with crops for nutrients in the soil, reducing crop yields. Various herbicides are available to kill weeds but the problem is that they damage crops as well. That’s why farmers welcomed the introduction in the 1990s of soybeans and corn that were genetically engineered to resist the herbicide glyphosate. Fields could be sprayed to wipe out weeds without harming crops. Yields and profits increased. But in the long run, you can’t beat biology. It was no secret from the beginning that eventually weeds would develop resistance to glyphosate.

This is what farmers are now seeing. The lifeblood sucking weed that corn, cotton and soy growers are worried about is called palmer amaranth. It has already devastated cotton fields in the south and is moving into corn and soy fields in the Midwest, probably introduced by manure from cows fed cottonseed contaminated with palmer seeds. Short of pulling out weeds by hand, which is possible but very labour intensive, farmers will have to look for new technologies. On the horizon are crops that have been genetically engineered to resist 2,4-D and glufosinate, two very effective herbicides that traditionally cannot be sprayed on growing crops because they will kill them just like they kill weeds. But 2,4-D will kill weeds that are resistant to glyphosate and will not harm the crops that have been engineered to resist the chemical. Of course this isn’t a long term solution because the weeds will eventually develop a resistance to 2,4-D as well. And 2,4-D doesn’t have quite as good a safety profile as glyphosate. Weeds that cannot be destroyed by herbicides are a farmer’s bane, and eventually, like Audrey Jr. they come out on top.


Joe Schwarcz

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