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Unsilent spring

The funny thing about farm chemicals is they’re a lot less scary when you learn a bit about them — and some of the cautionary tales from the past have actually shown us how to use them more safely and effectively

spray applicator in a canola field

Back in the early ’80s, when I was a science student, I took a pollution geography course and wrote a term paper on pesticides. I read Rachel Carson’s Silent Spring, the book credited with birthing the modern environmental movement, and dug through the library for all available references. I wound up getting a pretty good mark for what the prof called a very informative paper. I knew everything an urban college kid should know about pesticides and figured if we imposed a worldwide ban, then everything would be beautiful.

For the last 10 years I’ve been a science journalist producing articles for the farm press and that means I’ve been writing about pesticides. I’ve talked to agronomists, chemists and farmers, as well as academics and regulators — in short, a whole lot of people I didn’t know about when I wrote that paper. Now I know about half of what I need to know about pesticides and figure that if we impose a worldwide ban, then everything will be beautiful. Except for the mass starvation and malaria.

Agriculture is a much more complicated trade than I realized back in the ’80s and there are a couple of things today’s science journalist would explain to yesterday’s science student. One is that there are no simple solutions to the complex problems attached to growing plants and animals in a profit-based business model. The second is that we know a lot more about pesticide toxicology than we did before DDT was banned and, in a perverse way, DDT may be the reason why. 

The first rule of toxicology states that a poison will only kill you if you get a sufficient amount of it; the dose makes the poison. For example, I was at a conference where McGill University chemist Joe Schwarcz slapped up a transparency with a long list of the chemicals that you’ll find in an apple. He pointed to a nasty little poison called arsenic but he said it was perfectly natural to find it in the same fruit that keeps the doctor away. 

He explained that there’s always a certain amount of arsenic in the environment, it’s in your food, but the amount is so small that it’s of no concern. Your body can handle tiny measures of it. But we know arsenic is poisonous and we fear chemicals, and just knowing they are there scares some people. Psychologist Paul Slovic calls this “intuitive toxicology,” when we recoil from something that we feel is contaminated. If it can do harm, then it must do harm.

Our modern fear of chemicals probably goes back to Silent Spring and DDT. DDT, or dichloro-diphenyltrichloroethane, was first synthesized in 1874 but its insect-killing ability was first described in 1939 by Swiss scientist Peter Hermann Muller. He was awarded the Nobel Prize in physiology and medicine as a result. 

What a find it was too. DDT was used widely to eliminate the malaria-carrying anopheles mosquito and as a powder treatment for lice. In terms of public health, DDT was responsible for saving countless lives that might have been lost to insect-borne disease. When it was applied to farming, it created a revolution in pest control and those farmers reaped the bonanza. We learned the promise of chemical agriculture.

We also got our first taste of the consequences of chemical agriculture. DDT is fat-soluble, so it won’t dilute in water. If you’re a bug and you get a sub-lethal dose, you’ll store it in your fatty tissues and it tends to stay there. If something like a fish or a bird eats you, your predator gets your full dose, as well as everything it got from eating your friends and family. The concentrations go up as you travel on up the food chain. At the top (and that’s us) it rises to an even greater level and this is called bioaccumulation. DDT was in the environment and it didn’t break down fast enough so it caused a lot of trouble with different species of birds and animals. Since it’s fat soluble, it was easy to find.

Another thing DDT taught us was an uncomfortable truth in a brand new science called genetics. Down in the cotton fields of the southern U.S., boll weevils took their annual drenching, but instead of dying as they had before, they marched on through the fields and decimated the crops. Certain genetic combinations were resistant to DDT, so killing the vulnerable weevils left only resistant parents and they begat resistant offspring. Insects became immune to a deadly and persistent insecticide. 

We had to ban it but I might say it was because of DDT’s long life and the boll weevil’s selective resistance that we learned some of what we really needed to know about chemical agriculture. Of greatest importance, we simply couldn’t spray toxic chemistry around without regard for the consequences. 

I’d tell that to the science student, and explain that nowadays any new chemistry undergoes intense scrutiny through the Pesticide Management Review Agency before it’s registered for use. Then I’d show myself the label on the package that outlines the directions for best possible efficacy. I’d talk about spraying and how farmers are instructed to spray under the right conditions. I’d mention how it’s usually done within a certain time period so the chemistry has a chance to work and after that it starts to degrade into its different components.

Then I’d show myself a list of banned pesticides, just so I knew we weren’t complacent in all this. I might mention the use of seed treatments, an effective way to aim an insecticide right at its target without foliar spraying. I might also point out that, due to an unfortunate incident with bees around cornfields in Ontario in 2012, new seed coats are under development and the results are promising. If new problems crop up, we look for new ways to solve them.

Then both of us would talk about a NOVA program — the PBS science series — we saw back in the late ’70s where we were introduced to the concept of Integrated Pest Management (IPM). This was a new idea that suggested pesticides should be used as needed rather than as insurance. Pest populations were measured and, if the numbers were high enough, then farmers would spray. On the other hand, if spraying cost more than the estimated crop loss, then they wouldn’t spray. Although they might lose some production, they would actually save a little money and pest populations were less likely to develop resistance.

Another thing I might mention to my earlier self are the interviews I’ve done with entomologists about biological control. There are a number of pest insects that are effectively managed with predatory beetles and parasitoid wasps. I’ve talked to others about fungal sprays that kill grasshoppers and then there’s Bt genetic modification. Spraying isn’t the only option but, if done when needed, it’s still very effective.

A lot has changed since we started spraying. We’ve developed an impressive array of new chemistries to replace the older outmoded ones and we’ve developed much better protocols for their use. Our analytical chemistry and environmental monitoring are more accurate so we’re much better at doing more with less. Farmers are a lot cagier about using these compounds, and the equipment they have is improving.

The last thing I’d tell myself is what a career farmer told me. I asked him about insecticides and he said he used them as he felt he needed but he used them as a last resort. There are an awful lot of little friends out in those fields and taking them out doesn’t do you any favours.

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