Why Pesticides Are Actually Important for Agricultural Sustainability
I know that some readers will find my title surprising or offensive, but I hope you will read on. I’m writing this because I’m involved in a “broad stakeholder process” that is trying to define “scientifically sound metrics” to measure the sustainability of specialty agriculture (fruit and vegetable crops…). Its a very ambitious effort and probably the most ambitious when it comes to defining a measure of “sustainable pesticide use.”
On one level it could seem simple. Pesticides have to be used (even in Organic) otherwise the yield of farming would be too low and the land, water, energy and labor invested in a crop would be compromised or lost. Not all pesticides are the same (They actually differ rather dramatically in terms of their particular risk factors or lack therof. All meet rigorous EPA-determined risk standards when used according to the detailed EPA label limitations, but that still does not mean they are the same).
So, the answer might seem simple. Just pick the option with the least risk and you will be the most sustainable, right? From the perspective of an environmental organization, the key risk factors are for humans (workers, consumers) and for the environment (birds, bees, fish, earthworms…).
Unfortunately, the problem is that it isn’t that simple. When you get into the details of what it takes to grow each particular specialty crop there are a whole lot of other risks (and benefits) that have to be considered in the decision of whether to use a pesticide and which one. I’d like to give just a few specific examples of where sustainability depends on pesticides in unexpected ways.
Pesticides that Protect Consumers from Far More Dangerous Toxins
There is a moth called the Navel Orange Worm (NOW) that attacks tree nut crops. The larvae eat their way into the developing nut while it is still in its green husk. If a grower was only concerned about yield of nuts, not many insecticide sprays would be needed to produce an economically viable crop. Unfortunately, these larvae not only injure the nut, they tend to inoculate it with the spores of a fungus called Aspergillus flavus. That fungus then produces a toxin called aflatoxin which is the most potent natural carcinogen known. As I’ve said in a previous blog, the food system in the developed world does a remarkable job keeping this terrible toxin out of the human food supply. In the developing world this is one of the most frequent causes of death (liver cancer, immune-suppression).
In the case of tree nuts, prevention of aflatoxin contamination is accomplished by applying more pesticide sprays than would be needed just for yield protection. The growers are also using other cultural and IPM methods, but this is definitely a case where using fewer or lower risk pesticides would NOT be the right “metric”. We need the growers to continue to use what works to protect us.
Pesticides That Allow Non-Pesticidal Methods to Work
When I started graduate school in an agricultural field in 1977, Integrated Pest Management (IPM) was a brand new field. Since that time it has gone a long way towards helping growers successfully grow their crops with minimum possible risk to the environment and us. One of the particularly cool methods that is used is called “pheromone mating disruption.” Many male insects find their mates by following the “scent” of the pheromone chemicals that the females produce. One important IPM strategy is to put up a bunch of sources of the same pheromone chemicals throughout something like an apple orchard so that the males can’t find any real gradients leading to a female, and so little mating occurs because of this “disruption”. Little mating, fewer pests in the next generation. This method works great as long as the overall population of the pest in a given area is quite low.
IPM At Risk
Take the example of the Codling Moth (the most troublesome pest of apples – damage shown above). With this insect it is common for local population “hot spots” to develop that soon overwhelm the IPM method of “mating disruption”, not just in that spot but over a large area (these things fly). The only way to prevent this is for the growers to do lots of trapping and scouting so that when a “hot spot” develops, they spray it with Azinphos-methyl , a seriously “old school” pesticide, but something that has been just about the only thing that can save the IPM approach on the surrounding acres (that may be changing soon). 30 years ago, Azinphos was what was routinely used every 21 days on all the apples. In recent years it has played only a minor, but critical role in making it possible to use the “soft” IPM approach. This is a higher risk pesticide that lowers the overall risk spanning multiple adjacent orchards. How do you count that in a sustainability metric? (by the way, the mycotoxin patulin can occur in even minor codling moth damage)
I will follow-up with additional crop-specific cases where pesticide use decisions (and sustainability assessments) get complicated.
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