2011 21.4 Organic Fire Blight Control & the NOSB
For the past several decades, the most common control for fire blight has been the use of antibiotic sprays along with a predictive model of disease development. The National Organic Standards Board (NOSB) is considering revoking the most widely used antibiotics for controlling fire blight in Washington State and North America on a whole, tetracycline and streptomycin, from its approved products list.
Fire blight is a plant disease caused by the bacterium Erwinia amylovora. It is native to North America and resides in wild hosts such as crabapple and hawthorn. Apple and pear orchards in the Pacific Northwest are at risk from this disease. A serious infection does not occur every year in every orchard, but constant vigilance is required to keep orchards healthy. The most common infection route in this region is through the blossom, therefore,
monitoring and control is most critical at bloom. The disease can be vectored in many ways, including honeybees, other insects, birds, rain, wind, and hail. Once a tree is infected, the bacteria travel downward in the tree’s vascular system, can kill the entire tree, and can rapidly spread to infect an entire block. (see Figure 1) The economic consequences can be devastating.
Antibiotics versus biocontrol
Streptomycin and tetracycline have long been key disease control materials for fire blight. Streptomycin is now generally ineffective in the Pacific Northwest because of resistant disease strains, while tetracycline can provide 85-95% control if application is timed correctly. The two antibiotic materials used today throughout North America are oxytetracycline and streptomycin. The former is primarily used in our region, while Midwest and Eastern growers rely on the latter. Besides antibiotics, growers have other tools to prevent and control fire blight, including plant genetics, sanitation, removing diseased limbs, managing nitrogen and water, antibiotics, copper, and biocontrol products. However, biological controls have been researched and developed continuously since the 1980s, but to date, no control has proven equal to antibiotics. Michigan State University researcher George Sundin et al. (2009) tested numerous biocontrols over seven years in Michigan, New York, and Virginia, and found that “the prospects for biological control of fire blight in the eastern United States are currently not high due to the variability in efficacy of existing biological control options.”
Educating the NOSB on “Alternatives”
When the National Organic Standards were being drafted, the two antibiotics, both considered synthetic products because of their manufacturing process (they are naturally occurring compounds produced by microorganisms), were put on the National List of Allowed Synthetics. It was specified, however, that they could only be used for fire blight control in organic apples and pears [NOP Subpart G Section 205.601(i)9-10)]. Materials on the list are reviewed every five years as part of the sunset process to determine whether their continued use is justified or whether a suitable organic compliant alternative has become available. Since tetracycline and streptomycin are the only allowed uses of antibiotics on organic foods, there has been pressure to phase them off of the list. Various interests have put forward justification over the years, while growers have cited lack of effective alternatives.
In 2006, the National Organic Standards Board (NOSB) cast a mixed vote (7 yes, 4 no) to renew the two antibiotics until the next sunset. Then the NOSB received a petition in October 2007 to change the annotation to the use of oxytetracycline by adding another chemical form of it. This triggered a review independent of the sunset process (slated for 2011) and would have reset the sunset clock for another five years. However, on November 19, 2008, the NOSB changed the annotation to include both forms of tetracycline, and added the expiration date of October 21, 2012. The USDA accepted this recommendation as a final rule in 2010. The majority of NOSB members appeared to support phase-out as soon as possible. Streptomycin was slated for sunset review and a similar phase out in 2011.
Washington State organic orchardists were surveyed in February 2010 for their response to this regulatory change. Eightytwo percent of the respondents said they would not be able to control fire blight in a high infection risk year (CougarBlight model >700-800) without antibiotics (Figure 2), given the available alternatives. Many growers anticipated reducing their organic apple and pear production based on the loss of tetracycline. Organic growers in the Upper Midwest and Pennsylvania were also polled and generally said that antibiotics are crucial for fire blight control. Since Washington State produces the vast majority of organic fresh market apples and pears in the U.S., the loss of tetracycline would likely diminish the supply of these products at the same time that domestic and international market demand is growing. The Washington State Horticulture Association submitted a petition to the NOSB to remove the annotation regarding the phase-out out date for oxytetracycline. The petition was put on the docket, along with the sunset review of streptomycin, for the April 2011 NOSB meeting in Seattle. The meeting location allowed many affected growers to testify in person.
The testimony and discussions at the Seattle meeting were lengthy and illustrated the complexity of fire blight. Many NOSB members did not understand the nature of fire blight, the effective control options available, and the levels of risk and loss growers face with the disease. A significant part of the justification for the phase-out was based on presumed availability of alternative controls and resistant varieties and rootstocks.
Alternative controls are registered for use, but have not performed consistently or with the same efficacy as antibiotics. According to Tim Smith, WSU Extension and a world expert on fire blight, all pears are considered quite susceptible to the disease. Apples have a wider range of susceptibility, but none are truly resistant. An extension bulletin from Colorado State University states that “[c]ultivars of apple, crabapple, and pear differ in their degree of susceptibility to the bacterium…although some cultivars are less susceptible than others, no cultivar is immune to infection when the pathogen is abundant and conditions are favorable for infection.” Thus full resistance, or immunity, is NOT currently available to growers.
‘Red Delicious’ apple is one of the less susceptible varieties, but it is also one of the least desired by organic consumers. ‘Gala’ and ‘Fuji’ are produced on the most organic acres in Washington, and ‘Gala’ is more susceptible. This presents a conundrum to growers: should they choose a variety principally on the basis of consumer demand or a disease trait?
There is a new project using marker-assisted breeding to find sources of resistance from Malus sieversii, a wild apple relative that could lead to NOP compliant resistant varieties in the future. The NOSB repeatedly referred to resistant rootstocks, especially the ‘Geneva’ series from New York, as a reason to phase out antibiotics. These look very promising, but are not yet commercially available because of propagation problems. Also, a resistant rootstock does not confer resistance to the scion (top) of the tree, which is where infections occur (primarily through the blossoms).
NOSB might also consider that switching a rootstock in an orchard isn’t like changing a wheat variety in a seed drill. Replanting an orchard is a $15-20,000 per acre expense. Introducing a new variety into commercial channels is a multimillion dollar proposal that can take years.
After much debate and numerous revisions to the committee recommendations, the NOSB voted to extend the expiration date for oxytetracycline to October 21, 2014. The same expiration was voted for streptomycin under the sunset review. Statements can be found at http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5091701 and http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5091714. NOSB members asked the industry to create a task force to monitor progress towards alternatives, which has been initiated by Washington State University and Michigan State University, with support from the Organic Trade Association. The Organic Tree Fruit Industry Working Group will provide updates to the NOSB and try to help them objectively assess whether suitable alternatives to antibiotics are ready by October 2014.
Ongoing Research in alternatives
In the meantime, research on non-antibiotic fire blight control continues. Dr. Ken Johnson, Oregon State University, was awarded a USDA OREI grant to continue his work on fire blight control in organic fruit. He will collaborate with colleagues in Washington and California to test new products and integration of existing tools and management practices. Several growers have tried a non-antibiotic regime and report success so far.
A new yeast product from Germany called Blossom Protect® shows promise in initial trials. This yeast is naturally occurring in Washington orchards and was screened for its potential use a number of years ago by Dr. Larry Pusey, USDA-ARS fire blight research in Wenatchee. There are plans to investigate it, other biocontrol agents such as Pantoea agglomerans or Bloomtime Biological®, as well as the potential to use bacteriophages (a virus that attacks bacteria) against the fire blight organism. Interestingly, some of the biocontrol agents available or being developed produce antibiotics to control the fire blight bacterium, which work similarly to the antibiotics being phased out by NOSB.
In addition, Tim Smith has recently upgraded the Cougar Blight predictive model for fire blight that is routinely used in Washington to decide if and when to treat for the disease based on the weather (http://county.wsu.edu/chelan-douglas/agriculture/treefruit/Pages/Fire_Blight.aspx). And new diagnostic tests are becoming available, such as the LAMP test developed by Ken Johnson to determine the presence/absence of active fire blight bacteria in an orchard.
Listen to the growers
The April discussion around resistant germplasm highlighted the complexities of this issue and the challenge posed to NOSB members who typically do not have the technical background to understand it. The board members, all volunteer, are confronted with huge and expanding workloads. They generally do not have the technical expertise to evaluate many of the issues they are deciding on and must rely on expert input, stakeholder testimony, and fellow board member recommendations. They are trying to balance conflicting interests of different stakeholders and support the organic sector. However, it is apparent that the biases of an individual or two on the board can shape recommendations without adequate checks and balances from potentially affected parties. Growers need mechanisms to ensure their voices and concerns are heard by NOSB, something that groups such as Tilth Producers of Washington could help develop.
Organic growers are vulnerable to the particular expertise and biases of the board members, whose decisions can have a dramatic impact down on the farm. Given the recent fire blight experience, the interests of growers need to be better represented in the process and the board should be more pro-active in soliciting representative grower input regarding decisions that could have large negative impacts. The realities of production and the market must be considered by the NOSB and their decisions should allow for growers to make orderly change of practice without undue disruption of their efforts to provide organic foods. While getting involved in the NOSB process is extremely time consuming, the more members of the organic community that do so will definitely help improve the process over time.
Sundin, G.W., Werner, N.A., Yoder, K.S., and Aldwinckle, H.S. 2009. Field evaluation of biological control of fire blight in the eastern United States. Plant Disease 93:386-394.
Tags: Alternatives, Anitibiotics, Antibiotics, Biocontrol, Disease Management, Streptomycin, Tetracycline, Tree Fruit