Study on organic and conventional potatoes

Scientists from Washington State University and the University of Georgia have provided the most compelling evidence to date backing up a widely accepted principle of organic farming – in diversity, there is both stability and resiliency, according to The Organic Center. Crowder and others studied organic and conventional potato fields in Washington State, analysing the impact of species diversity and the evenness of populations on pest control and feeding damage in several ways. They refered to the degree to which any one organism dominates an ecosystem. In conventional potato fields, they found that "just one species accounted for up to 80 % of individuals..." while in the organic fields, the dominant species never accounted for more than 38 %. 

In their field work, the higher degree of evenness in the organic potato fields "translates into pest densities 18% lower and plants 35 % larger." In a meta-analysis of 38 published studies on predator-prey levels and impacts on yields, the team concluded that "natural enemy evenness increases yield." After explaining that conventional, pesticide-based control systems disrupt species diversity and tend to create ecological niches filled by a few highly dominate species, the authors conclude that "...organic farming methods mitigate this ecological damage by promoting evenness among natural enemies....very even communities of predator and pathogen biological control agents, typical of organic farms, exerted the strongest pest control and yielded the largest plants."

According to The Organic Center, the Washington State conventional potato industry remains remarkably pesticide dependent. The USDA's National Agricultural Statistics Service (NASS) last surveyed pesticide use by Washington's potato farmers in 2005. The average acre of WA conventional potatoes that year was sprayed with 17 pesticides, including six high-risk organophosphate and carbamate insecticides. An average of 14 pounds (6.3 kg) of pesticide active ingredient were sprayed on WA potatoes that year. This total includes 8.8 pounds (4 kg) of fungicides, 2.1 pounds (1 kg) of herbicides, and 3 pounds (1.4 kg) of insecticides. The above totals do not include the average 103 pounds (46.5 kg) per acre (0,4 ha) of "other pesticides" applied on Washington State potato fields. These other pesticides include the soil fumigant metam-sodium, which is applied at a rate of 158 pounds (71 kg) per acre and dichloropropene (applied at 160 pounds / 72 kg per acre). For the full details, The Organic Center has posted a table summarizing Washington potato pesticide use in 2005.
 

The Organic Center