Issue link: http://read.dmtmag.com/i/138107
What risk do antibiotics pose? Use of antibiotics in tree fruits is tiny compared with use in animal production. by Geraldine Warner ne of the main drivers behind campaigns to ban the antibiotics oxytetracycline and streptomycin from organic fruit production is the public's fear that their use could reduce the effectiveness of medicinal antibiotics in humans. Dr. Steve Lindow, plant pathologist at the University of California, Berkeley, said there's some justification for that view; there's clear evidence that use of antibiotics in animal production can increase the number of antibiotic-resistant genes in the environment and that these genes can be introduced into human pathogens. It's therefore thought possible that the same scenario could apply with antibiotics used on plants, though there's no evidence yet. "It's guilt by association," he said. However, the volume of antibiotics used on fruit trees is tiny in comparison to the amount used in animal production. David Granatstein, sustainable agriculture specialist with Washington State University, said it's been estimated that only about 10 percent of pome fruit growers in the country apply antibiotics in any given year. The products are applied in bloom, and leave no residues on the fruit. A scientific study in Oregon showed that oxytetracycline degrades rapidly on the tree or in the soil and is gone within a week of application. And, a study in Wisconsin that found no difference in resistance genes in orchards treated annually with streptomycin for ten years versus orchards never treated. Human pathogens are rarely found on apple flowers or leaves, limiting the opportunity for transfer of resistance genes, Granatstein said. Scientists say that biocides, such as triclosan, used in household antibacterial soaps are of much greater concern because they are used so widely at sublethal concentrations that they promote bacterial resistance. blossoms. Biological controls work by colonizing flower stigmas, where it is hoped that they will build up to sufficient numbers to exclude the fireblight bacteria and prevent infection. Some biocontrols produce their own antibiotics that partially control the disease. Lindow, who developed Blight Ban (Pseudomonas fluorescens A509), said that biocontrols are useful in reducing the need for antibiotics, but are not total replacements and are not as effective as streptomycin where the fireblight organism has not developed resistance to it. Growers are "between a rock and a hard place," he said. "Biologicals are very helpful. They can be integrated with antibiotics so we can reduce the amount of antibiotic, but, normally, we would have considered both together in some way." • Opposite effect The decision of the National Organic Standards Board not to extend use of the two antibiotics beyond 2014 is likely to have the opposite of its intended effect and increase the amount of antibiotics used in apple and pear production, Granatstein warns. Surveys he has conducted show that between 70 and 90 percent of Washington organic growers would reduce their acreage of organic apples and pears unless there's a proven alternative, or drop their organic status entirely so that they could protect their orchards with antibiotics rather than lose trees. Since the late 1990s, there's been extensive work to develop biological controls for fireblight, but with limited success. Biological fireblight controls work in a different way from antibiotics. Properly timed applications of antibiotics kill the fireblight bacteria before they are able to infect the tree, usually through the www.goodfruit.com Domex Superfresh Growers®, owned by the Kershaw family, is using the power of social engagement to connect growers to consumers. We are achieving reliable performance with exceptional sales and marketing for our family of growers while delighting consumers everywhere. Call us today to learn more about growing with Superfresh Growers®. We know what's trending NOW. Our difference makes all the difference™ 151 Low Rd., Yakima, WA. 98908 | superfreshgrowers.com GOOD FRUIT GROWER July 2013 17