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Jan
12
2009
Organic farms surprisingly vulnerable to pest invasion
Conservationists sometimes tout biodiversity a lot like salesmen of centuries past promoted magic health elixirs – a cure for all your ails. But for organic farmers who buy the claim that a wider array of species will automatically control crop pests, the authors of a new study have one thing to say: Don’t bet the farm on it.
Writing in Ecology Letters, the researchers surveyed 10 pairs of organic and conventional farms in southwest England, and, indeed, found that organic farms harbored more plant, herbivore and parasitoid species, the latter of which can be fatal to crop-munching insects. But when they introduced a new, unknown insect—a leaf miner—to the systems, the parasitoids on organic plots proved no more capable of controlling the invasion. On organic lands, parasitoids colonized up to 47 percent of the leaf miners, a number that was no different, statistically, than the 63 percent on the conventional plots. Similarly, parasitoid biodiversity had no effect on natural pest control rates within the larger survey pool.
As governments pour money into stemming the tide of biodiversity decline on intensively farmed lands, the results provide a dose of truth-in-advertising about some of the perceived benefits.—Jessica Leber
Source: Macfadyen, S. et. al. 2008. Do differences in food web structure between organic and conventional farms affect the ecosystem service of pest control? Ecology Letters DOI: 10.1111.j/1461-0248.2008.01279.x
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Filed Under Biodiversity, Habitat, Restoration |
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This is a straw man. I don’t ever recall anyone ever saying that organic farming techniques will “automatically” protect them against crop eating insects. The text here is very deceptive. The salient question is whether the leaf miner species deliberately introduced had any specific prey species in the studied plots. If no specific prey species for that leaf miner were present in the test plots, then it is only logical that the leaf miner would have free rein, regardless of whether the plot is “organic” or conventional. In a real organic gardening situation, as soon as the leaf miner appeared, the gardener/farmer would seek to identify the leaf miner, identify a potential treatment, and apply it. “Organic” does not mean you just hope that whatever is in your garden is a priori sufficient to protect your plants from pests. You still have to do the work.
Thx.