Sunday, September 6, 2009
A plant's natural defense system
For those of you that know me, you are aware that I am not a proponent of "spray-and-pray" applications of pesticides. While pesticides are an important component of agriculture today, I hope that through science and sound decisions we will be able to support ourselves with a limited use of these products in the future.
In my experience, it seems that many people do not realize the risks associated with pesticides to themselves and the environment. If the label says to apply one ounce, then two must be better, right?
While I consider myself to be an environmentally-minded person, I hesitate to categorize myself -as my friend Chip says- as "hippie-sensitive". Rather, I like to form my perspectives based on science. So here it goes:
Over the last eight years, I have noticed that plants that are treated frequently with pesticides are more susceptible to leaf spots and blights than plants that are never sprayed. What I mean is that as long as the plants are regularly sprayed, they are fine. But miss one application and the plants quickly lose their leaves or become covered in spots. Why?
In Michael Pollan's book In Defense of Food: An Eater's Manifesto, I found an answer that seems based on real science. A lot of research has been conducted over the last couple of decades on the nutritional differences between organically and conventionally grown fruits and vegetables.
Results from this work shows that in "addition to these higher levels of minerals, organically grown crops have been found to contain more phytochemicals- the various secondary compounds (including carotenoids and polyphenols) that plants produce in order to defend themselves from pests and diseases....Because plants living on organic farms aren't sprayed with synthetic pesticides, they're forced to defend themselves, with the result that they tend to produce between 10 percent and 50 percent more of these valuable secondary compounds than conventionally grown plants." (Pollan, 2009)
Over 30,000 secondary metabolites (phytochemicals) have been identified in plants, including Neem extract and pyrethrum. These metabolites are not necessary for plant development, rather they are produced by plants as a natural defense system.
So what he's saying is that in nature, animals and plants do not waste precious energy on things they don't need. And if a plant is being protected from insects and disease with pesticides, it is not going to create the same amount of protective phytochemicals. They will instead put that energy into growth and reproduction.
We seem to collectively agree that this is true when humans are on a steady diet of antibiotics, that they will be more susceptible to sickness if they stop taking the medicine. At least temporarily this is true. And the same is true for plants.