Search is on for tetracycline replacements in organic orchards
By STEVE BROWN
PORTLAND -- Though researchers have tested several treatments that may be able to replace oxytetracycline in organic apple and pear orchards, they say they need more time to find the most effective way to fight fire blight.
The antibiotic has been the treatment of choice, but its use in organic orchards is due to expire in 2014.
When the National Organic Standards Board meets in Portland April 9-11, its crops subcommittee will propose extending the expiration date to 2016. The sunset date had previously been postponed to allow more time for the development of effective alternatives.
The industry's long-term goal is to develop host resistance, said Ken Johnson, professor of plant pathology at Oregon State University. But in the meantime, treatments are being developed to deal with floral infection in susceptible cultivars:
* The National Organic Program has approved the use of fixed copper for pre-bloom application, but results have ranged from poor to good, he said.
* Being tested for the early bloom stage of pears is Bloomtime Biological, with poor to good results. The use of lime sulfur and fish oil on apples has had good results.
* New in 2012 was Blossom Protect, a yeast product that has shown good to excellent results in the mid- to full-bloom stage. Tim Smith, with Washington State University Extension in Wenatchee, said the yeast is a natural organism common in the Pacific Northwest. The cost is about double that of antibiotics.
Rachel Elkins, farm advisor with University of California Cooperative Extension in Lakeport, addressed the likelihood of the yeast product causing russeting in Bartlett pears. There was plenty of rain in 2011, she said, and one application led to russeting; 2012 was drier, and it took three applications to cause any increase.
Elkins plans to set up commercial-scale tests of the product.
* A copper product by Gowan, called Previsto, has been excellent in treating the pathogen at full bloom and beyond. It still needs Environmental Protection Agency registration, expected by this July, Smith said, as well as approval by the NOP. The components of Previsto have been accepted as organic, he said.
In a webinar by extension.org, the researchers described their work in "integrated control" with the non-antibiotic substances.
Johnson said the researchers found success using a delayed dormant fixed copper in orchards with fire blight history, thinning apples with lime sulfur, applying Blossom Protect near full bloom, and using soluble copper at later bloom as a substitute to oxytetracycline.
It will take time to fully research the different materials, he said, "but this is doable."
The only U.S. pear breeding program focusing on fire blight resistance is in West Virginia, Elkins said. She called blight "the limiting factor" for Eastern pear growers.
Smith said the effectiveness of resistance is relative, not absolute.
While waiting for new cultivars and new products, he said, "The most important factor is sanitation in the neighborhood. One (fire blight) canker can affect an area of three or four acres."