Monday, March 9, 2009

Organic Pest Control

The chemistry of life is a funny thing. Different animals respond differently to the same chemical. Catnip is a perfect example. To humans, it makes a tasty tea, somewhat like mint. To cats, it is a mind-altering drug. To cockroaches, it is extremely noxious. Scientists have found that a catnip tea spray is 100 times more effective as a roach repellent than anything commercially available. The only problem is that you have to re-apply every day or every other day at the least.

Plants have no ability to move like animals do to defend themselves, but defend themselves they do. Plants have evolved a number of chemical defenses to protect themselves from being eaten. They have become experts in chemical warfare. Some defenses kill, some irritate, some cause pain, some are just unpleasant to be around. Marijuana makes its predator forget where they found food. We humans are kind of funny. We have developed this wonderful technology called culinary skills that allows us to dilute and combine the various chemicals that plants use to defend themselves to make our food more interesting. Now, I am not saying that all of our culinary herbs and spices are effective as pest repellents, but there is good reason to believe that many are. So here are a few known examples of foods that can be used as repellents:

Fruit is a bribe. The plant puts seeds that are capable of surviving the digestive system in a tasty coating so that animals will eat the fruit, seeds and all, and then deposit just the seeds in a new location with a handy lump of fertilizer. So why would a plant create a fruit that causes abject pain when eaten? Well, it turns out that capsaicin, the chemical that makes chilies spicy, is completely undetectable to birds. So they can't really tell the difference between a blueberry and a chiltepin (the wild form of chili peppers). Why would a plant create a berry that is only edible to birds? Maybe they don't like to be chewed. We don't really know, and it doesn't really matter. The point is that nature has provided us with a chemical that is extremely noxious to mammals, but undetectable to birds. Some bird food manufacturers are using this knowledge to make birdseed that is squirrel-proof. Just sprinkle on a little chili powder and the squirrels won't touch it.

The last place I lived had a robust wild population of cockroaches. While they never got an established indoor population (yay, cats!), they did tend to get in every now and then. So I planted catnip around the house, particularly by the doors, in an attempt to allow the living plant to repel the roaches. It worked really well. It was particularly noticeable when the large bush by the front door died and the number of cockroaches both in the front yard and coming my house tripled. Earwigs, on the other hand, just LOVE hanging out in catnip plants. I don't know why.

The distinctive garlic smell and spiciness is actually the result of a chemical reaction between two chemicals in the garlic clove that don't mix until the cell walls are broken. So it doesn't release the weapon until it is actually damaged. Garlic is a non-specific repellant. It will drive off insects, mammals, women and just about everything else. There are several commercially-available garlic sprays that you can use to spray around your garden to repel a wide variety of pests. It is one of the more effective repellents for use against deer and rodents. At my current abode we have a rather large population of javelinas, also called banded peccaries. They are sort of a native wild pig. They like to roam around at night and dig up all the stuff you just planted just in case there is something tasty in the ground. I have a large pot full of plants I brought from my last house that I don't want them digging around in, so I also planted a bunch of garlic in there. So far, they have dug around in just about everything else, but they have avoided that pot. Some people also use garlic for personal pest control against mosquitoes and other biting insects. The application is simple: you just eat a yummy meal loaded with garlic. The garlic smell will start coming out of your skin and provide protection for a day or two. But beware! It also repels people.

Okay, I don't know of any specific properties of lemon that make it a repellant, but you have to admit that the ubiquity with which it appears seems mighty suspicious. It is a flavor signature that appears in dozens of different plants, many of whom are unrelated. It appears in citrus, lemon grass, lemon balm, lemon basil, lemon thyme, purslane, and many others. Generally, when a chemical evolves separately in that many plants, it is because it serves a very specific purpose. One of these day's I'll work on testing that theory. There's got to be a good use for it.


  1. What a great resource, thanks!

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