I’m sure you’ve heard that garlic is good for you. For thousands of years, all around the world, people have attributed health benefits to eating the so-called stinking rose. But it also turns out to be a big help in keeping some crops healthy.
Organic gardening books for years have recommended planting garlic in and around your garden to help repel pests. Unfortunately, there isn’t much evidence showing this to be effective, other than as a way to utilize small amounts of garden space to grow another crop. Instead, it is garlic oil, sprayed on crops, that turns out to be one of nature’s most effective pesticides.
Oils in general are effective pesticides — they coat and cover plant leaves, smothering a number of insect pests. Not every oil can be sprayed on plants though, without damaging the leaves or leaving undesirable residues. Meanwhile, certain natural oils — clove, rosemary and neem trees — are especially effective at killing pests. So is garlic.
But garlic has something that these other oils don’t have: natural sulfur compounds. These are part of what give garlic its unique flavor as well as its tendency to produce gas when eaten. Sulfur is also a natural fungicide, and the particular sulfur molecules in garlic are especially effective at killing several of the most destructive fungi that infect many crops. So garlic oil is not just an insecticide, it is also a fungicide.
We spray garlic oil on our table grapes. Not only does it eliminate powdery mildew, it also kills leafhoppers — a destructive pest that feeds on the leaves and can defoliate the vines. We also spray it on our onions, where it again does double duty: fighting downy mildew and killing a pest called thrips.
Sometimes we even spray garlic on, well, garlic. It turns out that the sulfur compounds in garlic cloves do not exist in the rest of the plant while it is growing. (This is why planting garlic in your garden does not do much to prevent pests) So the leaves are susceptible in wet years to a fungus called “rust” which, if left to spread unchecked, can kill the plants before they even have a chance to form bulbs. But garlic oil kills it.
The best thing about spraying garlic on our crops is how safe it is to use. While drinking a quart of garlic oil would give you pretty nasty heartburn, it is technically a food and the EPA does not even consider it a pesticide. Yet it works so well that some conventional growers have begun using it instead of much more toxic chemicals.
So on any given day of the year at Terra Firma, the smell of garlic may be wafting across the field, even if we have no garlic growing at the time. Oh yeah, and it also helps keep the vampires away.