(Beyond Pesticides, July 2, 2010) A study by researchers from Washington State University (WSU) and the University of Georgia suggests that a balanced mix of insects and fungi in organic fields provides for both better pest control and larger plants than in conventional agriculture. The study, which was funded by the U.S. Department of Agriculture’s (USDA) National Institute of Food and Agriculture (NIFA) and published in the July 1 edition of the journal Nature, shows that organic farming practices lead to many equally-common beneficial species, and that this reduces pest problems.
“It’s always been a mystery how organic farmers get high yields without using synthetic insecticides,” says co-author Bill Snyder, Ph.D., associate professor of entomology at WSU. “Our study suggests that biodiversity conservation may be a key to their success.”
The study involved 42 potato plots enclosed in fine mesh on the Pullman campus of WSU. The researchers planted both potato plants and Colorado potato beetles (a very problematic pest of the potato) in each of the plots, adding varying numbers of beneficial insects, fungi and nematodes, microscopic soil-dwelling worms that attack beetles’ eggs and larvae.
Crops placed in the organic test plots with a more balanced insect population grew faster, because no one species of insect had a chance to dominate the plot and kill the potato plants. In fact, the study found that the increased evenness of species in the organic plots compared to the conventional plots led to 18% lower pest densities and 35% larger plants. Larger plants generally translate to greater potato yields, suggesting that organic methods might provide higher profits as well as an ecological sustainability advantage.
Though previous conservation and biodiversity studies tended to focus on species richness, or the number of individual species present in an area, this study is one of the few to consider the advantage of relatively equal numbers, or “evenness” of species for a beneficial agricultural ecosystem. Thus, the results show that both richness and evenness must be maintained to ensure a healthy environment. Conventional agricultural methods, which rely heavily on spraying pesticides, tend to wipe out the majority of insects, leaving behind a few hardy species that end up dominating the conventional field ecosystem. These findings promote the reliance on a mix of natural predators as a way to avoid the “pesticide treadmill” that forces farmers to use larger and larger volumes of different costly chemicals to kill hardy pests that develop resistance.
Research director Andrew Jensen from The Washington State Potato Commission, which partially funded Dr. Snyder’s research, says they hope to translate the study into practical advice their members can use. Washington is second (after Idaho) in potato production in the U.S., but less than 1% of the state’s potatoes are organically grown. Studies like these might convince potato growers to cut back on spraying and eventually switch to organic methods, which would suit top potato customers, like McDonalds and Wendy’s, who are being pushed to green up their practices.
“People who buy a lot of potatoes are asking the growers to reduce insecticide use as much as possible, to document pesticide use, and include biological control as a consideration,” remarked Dr. Snyder in a comment to the Seattle Times.
This study adds to the body of scientific literature considering the benefits of organic agriculture, which includes a paper published by the Rodale Institute in 2003, describing how an organic system produces better yields of corn and soybeans under severe drought conditions and gives better environmental stability under flood conditions through lower runoff risks and greater water retention capabilities in the soil. This helps to balance inaccurate, industry-funded studies which only confuse consumers.