The news finally broke last week, months after the first anxious reports of browning and dying trees near lawns and golf courses across America.  Unlike their wild cousins in the Rockies and British Columbia, these conifers aren’t dying of pest outbreaks – they’re suffering from pesticides.

It seems that Imprelis, a recently-released DuPont herbicide marketed for environmental friendliness, is poisoning ornamentals like Norway spruce and eastern white pine.  Now, DuPont is promising new labeling for Imprelis, the Environmental Protection Agency is reevaluating its approval, and New York and California are congratulating themselves for never approving it in the first place.  Add Imprelis to the list of pesticides whose ultimate toxicity took us by surprise.  At least this time we noticed the signs within six months, not 25 years, as was the case with DDT.

The herbicides, fungicides, and insecticides applied to lawns each year may seem the most gratuitous – at least to those of us who don’t mind a dandelion or clover here and there.  But it’s actually agriculture that applies 80% of the 1.1 billion pounds of pesticide used in the US each year, quelling insect outbreaks, smothering weeds, and ensuring un-nibbled produce.

Of course, when we nibble that produce – or eat animals who’ve nibbled it – any residues and leftover toxins transfer to us.  That’s one major reason why every single sample that the Center for Disease Control tested in 2007 contained traces of pesticide.

How did we become so chemically dependent?

Most of the story should be familiar:  It’s the tale of the Green Revolution, which tripled our agricultural yields.  By growing hybrid crops with shallow root systems and short stalks, farmers ensure that their plants dedicate the majority of their energy to producing big yields.  But these varieties also need babying: lots of water to keep shallow roots moist, fertilizer to support increased fruiting, and pesticide applications to knock out wilder, tougher neighbors and natural enemies.

Of course, pesticide application is not without consequences. In sufficiently high doses, some pesticides are acutely toxic to humans as well as their intended victims.  Low-level, long-term exposures can cause cancer, reduce fertility, and disrupt endocrine signaling.  And many of the compounds don’t break down right away, so they’re washed into waterways and may accumulate downstream – persistent pollutants acting in unintended ways on unintended targets.

Some new technologies have been developed to reduce this spillover (and, of course, make immense profits for their patent holders).

In 1996, Monsanto began marketing its Roundup Ready line – crop varieties resistant to the herbicide glyphosate (Roundup).  Glyphosate is believed to break down quickly on fields, theoretically providing a localized, targeted attack on weeds.  But beyond campaigns against genetically modified crops (nicknamed “Frankenfood” by protestors), there are real fears that glyphosate resistance could “escape” (through genetic reshuffling by cross-pollination) and take off in the wild weeds.  Repeated application of glyphosate on acre after rolling acre creates strong selection pressure in favor of any plant that evolves to tolerate the chemical.  Like antibiotic resistance, pesticide resistance can spread rapidly through populations, devastating food supplies and livelihoods.

To minimize such risks, Round Ready’s sister seed, Bt-corn, comes with a mandate that other corn strains be planted alongside it.  Bt-corn has been genetically modified to produce a toxin normally manufactured by the soil bacterium Bacillus thuringiensi.  This BT toxin is noxious to insects that would normally attack the corn: in fact, farmers sometimes spray the bacterium itself on crops.

Of course, any bug that developed a tolerance for BT toxin would have exclusive rights to a field full of juicy, fat ears of corn.  In other words, its reproductive fitness would skyrocket, and that field, and its neighbors, would be demolished by the lucky arthropod and its offspring.  In theory, though, any toxin-free corn nearby would harbor an abundance of the same species, but without resistant traits.  Hopefully, that first resistant bug would choose a mate from among the susceptible population, and the resistance trait would be lost in the genetic shuffle.  (Note that this only works if resistance arises from a recessive mutation, i.e. one in which two copies of the gene are necessary – one from each parent.)

But who wants to plant an offering for the enemy when Bt-corn is so profitable and successful?  At least one in four farmers was willing to dodge the law back in 2008, when the EPA surveyed US corn plantings.  With reports of resistance spreading in China and India, our time bomb could explode at any moment.

And so we find ourselves locked into another arms race with evolution, pitting our chemical engineering against the random luck of millions of mutating, adapting plants, insects, and fungi.  To fail is to surrender a huge and critical segment of our food supply.  But to prevail is to release more and more toxins deliberately into our environment, some of which will have side effects far deadlier than DuPont’s Imprelis.

Some people are bowing gracefully out of the dance, turning to the traditional methods of “Integrated Pest Management”.  They rotate crops, use mechanical pest traps, breed pest predators, and plant a range of plant varieties.  These are the tools organic farmers use – with the delicious success you can witness at weekend farmers’ markets, or in your own backyard garden.

Join me, for a bite.