Evaluation of Strategies for Management of Soybean Rust in Organic Systems

NON-TECHNICAL SUMMARY: There are no known NOP approved strategies to control Asian Soybean Rust (Phakopsora pachyrihizi) (ASR) in organic production systems. There are, however, some intervention and cultural strategies that hold some promise of efficacy. The purpose is to evaluate the following strategies for soybean rust: system effects, including extended crop rotations and windbreaks (to mitigate spore dispersal) and tools, including NOP-compliant fungicides, such as copper sulfate and hydrogen peroxide, and biological controls (Bacillus pumilus and other microbial products).
<P>

APPROACH: 1: We will compile a list of organic farms where rust has been confirmed and create a database of farmers using extended rotations (beyond a two-year rotation) and/or windbreaks, strip-cropping, or other practices that appear to restrict soybean rust in their organic soybean systems. <P>2: Biological or botanical substances included on the National List of natural and synthetic substances allowed for use in organic crop production will be applied to prevent, suppress, or control soybean rust.<P> 3: We will investigate the effect of these materials on organic soybean growth, yield and health (insect and disease pressure), and on soybean rust, should the disease arrive at these sites.
<P>
PROGRESS: 2005/09 TO 2008/09<BR>
OUTPUTS: Fortunately for the major organic soybean producing areas of the U.S., Asian soybean rust (ASR) did not reach an epidemic stage during the course of the project (2005 to 2008), despite isolated findings in Iowa in 2007 and other states outside of this project's scope. As of December 2008, ASR was reported in 396 counties in the U.S. Research supported by this project in Florida, where ASR has been occurring since 2004, led to the identification of viable strategies, including NOP-compliant copper-based fungicides, for effectively managing ASR in organic systems and mitigating losses in the event of severe infection. In addition, the application of natural silicon was investigated and found to delay ASR disease onset in Florida. Other successful pest management strategies included trap crops to prevent stink bugs from colonizing organic soybeans. In areas where ASR has not yet arrived, methods of improving organic soybean systems, including reduced tillage and varietal selection to mitigate other soybean diseases, resulted in greater maintenance of soil quality and higher returns for farmers. Over the three years of the project, dissemination of information to over 1,200 people has occurred through presentations at annual Field Days held in each state, and at the Iowa Organic Conference, Michigan Sustainable Farming Association Conference and the Upper Midwest Organic Farming Conference each year. On-line reports have been posted at the following sites: NewFarm, New Ag Network, OrganicAgInfo and each institutions' research farm and individual organic websites, including http://extension.agron.iastate.edu/organicag/. Through these efforts, we have increased the knowledge base and skills of thousands of organic farmers across the U.S. in Asian soybean rust diagnostic and management tools. Activities supported through this project in 2008 included the establishment of four research experiments in Florida, Iowa, Michigan and Pennsylvania; analyzing all data from sites; four state reports and one overall project report; three Field Days in Michigan, Iowa, and Pennsylvania; and the Florida site serving as a demonstration site for ag professionals receiving training in ASR. Products produced included new applied knowledge and technology for ASR management in organic systems, and the sharing of this information on websites listed below. A hands-on training of the latest technology for ASR detection, an ELISA strip test (EnviroLogix, Portland, Maine) was demonstrated to 68 producers and Extension personnel in Iowa on September 23, 2008. PARTICIPANTS: Participants in this project include Jerry DeWitt and Robert Turnbull (Iowa State University), Ann Blount, David Wright, Cheryl Mackowiak, Jim Marois, Richard Sprenkel, Steve Olson and Russell Mizell (University of Florida), Dale Mutch, George Bird and Mark Whalon (Michigan State University), and Jeff Moyer and Paul Hepperly, The Rodale Institute. Partner organizations include the Iowa Organic Association, Michigan Sustainable Farmers Association and the many outreach agencies through The Rodale Institute's efforts. Professional development opportunities for Extension and farmers from this project have included participation in Field Days and conferences described above.<BR> TARGET AUDIENCES: Target audiences have been organic soybean growers in the U.S. and in the world. Organic and non-GMO soybean processors are also interested in these results. Efforts include Extension-based dissemination, such as Field Days, conferences and on-line reports. <BR><BR>
IMPACT: 2005/09 TO 2008/09<BR>
Asian soybean rust (Phakopsora pachyrihizi) (ASR), arrived in the U.S. in 2004 and ranged to Canada in 2008. Because there was no organic-compliant control of ASR the purpose of this project was to evaluate tools, including organic-compliant fungicides and cultural strategies to limit damage from ASR. On-station organic fungicide efficacy studies in Florida, where rust has been extremely active and in Iowa, Michigan and Pennsylvania for their effect on yields and other soybean diseases were conducted. In Florida, an organic trial was established in 2005 to examine the effects of organic-compliant fungicides on ASR on soybeans grown on land in transition to certified organic status. Over all years, the most effective fungicides were copper hydroxide and copper sulfate when plants were rated according to the Horsfall-Barrett rating scale (0 = 0%; 11 = 100% diseased). At the highest disease rating period in 2006, soybean plants treated with Champion (copper hydroxide) and basic copper sulfate were rated 2.0 and 2.6, respectively, compared to the control at 7.4. In 2007, copper-treated plants averaged 2.6 compared to the control at 4.8. Yields were greater in these treatments in 2006 and 2007. There were few differences detected between the control and Bacillus pumilis, capryllic acid, Hoshizaki water, hydrogen dioxide, and microbial combinations (AN and MAF). These results suggest promise for copper-based products for organic management of ASR, but build-up in routine use of copper fungicides must be considered. Across all years, data have shown that in Iowa, Pennsylvania and Michigan, no significant differences in organic soybean yields were found in soybeans treated with Bacillus pumilis, an OMRI-listed fungicide that has shown some efficacy against ASR in South Africa. Other ASR fungicide products that were tested in this project showed no effects on yields or soybean diseases, although soybean oil in Pennsylvania caused some phytotoxicity in organic soybeans in 2007. Organic soybean yields were excellent in 2008 (averaging 53 bu/acre), despite significant flooding in Iowa in 2008. Diseases were low, despite long periods of flooding. Across all years, yields ranged from13 bu/acre in a severe drought year in Michigan in 2007 to 65 bu/acre in Iowa the same year. Later planting, a possible strategy for ASR management, led to equivalent yields if planting occurred before June 16. No significant differences in mite or natural enemy diversity, or nematode community structure were detected among the fungicide treatment or planting dates, but the population densities of bacterivores in organic plots were generally higher than those associated with conventional soybean production sites in Michigan. Another potential strategy, planting soybeans into a rolled cover crop, was evaluated for yield and disease effects. Across all years, the highest organic soybean yield occurred in Iowa in 2007, when yields averaged 45 bu/acre in a rolled cover crop of hairy vetch/rye with no rust detected and other soybean diseases ranging from 0 to 2.3% of leaves infected. As a result of this effort soybean producers now have an effective tool with which to counter ASR.