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Asian Soybean Rust: Notes and Organic Control Options for Farmers |
| By Holly Born and Steve Diver NCAT Agriculture Specialists © NCAT 2005 ATTRA Publication #IP282/282 |
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Table of Contents
Background on Asian Soybean Rust (ASR)What is Asian Soybean Rust?
There are two types of the fungal disease known as soybean rust: the less-aggressive Phakopsora meiboniae and the Asian form (Phakopsora pachyrhizi). Asian soybean rust (ASR) is the fungal disease causing immediate concern. It is a virulent pathogen than can quickly defoliate plants and reduce pod set, pod fill, and seed quality. It can reduce crop yields by 10 to 80%. Asian soybean rust has a wide host range and can infect more than 90 common native legumes, edible legumes, forage legumes, and naturalized legumes, including clover, vetch, lespedeza, lupine, and kudzu. In addition to soybeans, ASR can infect a wide variety of Phaseolus legume crops such as dry beans and green beans. Thus, ASR may also have a significant effect on vegetable farmers raising "green, string, snap, and wax" beans. ASR overwinters on live host legumes and sporulates the following spring. It cannot survive on dead tissue or crop residues. Wind-blown spores can travel for great distances. It is likely that ASR will survive on vast acreages of naturalized kudzu in the southern U.S. and thereby establish a permanent presence in the continental U.S. There are many environmental factors that effect occurrence of disease. Cool temperatures (68 to 75 degrees F), prolonged wet weather, high relative humidity (75 to 80%), and heavy dews are favorable for development of ASR. Soybean rust spores are easily transported in air currents and spread rapidly over wide distances. Studies have shown that under the right circumstances, spores can remain viable for more than 50 days. Quarantine measures, therefore, would not be effective in controlling ASR. A guide to identifying soybean rust (PDF / 6.5M) with photos, including "look-alike" diseases, is available from USDA-APHIS. Occurrence of Asian Soybean Rust (ASR) in the U.S. and BrazilSoybean rust was first detected in the southern United States in November 2004 and is expected to spread to other soybean producing regions throughout the U.S. during the 2005 and 2006 growing seasons, causing widespread infection and reduction of crop yields in the U.S. soybean crop. ASR was first detected in South America in 2001 and has since spread throughout the soybean growing regions of Brazil, Paraguay, and Bolivia. Many experts believe that outbreaks of Asian soybean rust in the U.S. will be less frequent and less serious than outbreaks in Brazil. The major soybean producing regions in Brazil have weather conditions that are more conducive to rust than those in the U.S. Dr. X.B. Yang, a leading soybean rust researcher at Iowa State University, says, "The information to date suggests that regional outbreaks in the Southern U.S. would be sporadic compared to central Brazil."(Yang, 2004) General Information and Advice on Asian Soybean Rust (ASR) ControlVarietal screenings conducted at quarantined research facilities by USDA have revealed that virtually all commercially grown soybean cultivars are susceptible to ASR. Some promising sources of resistance have been identified, but new varieties won't be available in the commercial trade for several years. Disease control options for ASR are limited. Rust descends in clouds of spores across the countryside. Cultural practices such as row spacing and crop rotations have little effect. Resistant cultivars do not exist. When weather and disease infection conditions are favorable, the occurrence of ASR can be widespread. Thus, remedial control measures—using fungicides as protective sprays—are the only effective disease control method. Synthetic fungicides are the primary disease control option for protection against Asian soybean rust. (See organic disease control options below.) The cost of spraying is estimated to be about $15 to $20 per acre; however, two or three sprays may be needed over the course of the growing season. These are significant additional production costs for soybean growers. These higher costs are expected to favor a shift to corn acreage in the Midwest and cotton acreage in the South. Fungicide screening trials to determine disease control efficacy have been field conducted in South America and South Africa. These reports are available on the Web through USDA's Integrated Pest Management Information Centers. These research trials form the basis for fungicidal recommendations in the U.S. Farmers are advised to monitor disease alerts from the Cooperative Extension Service at agricultural colleges and universities. Producers should also be prepared to monitor soybean fields and bordering lands for signs of rust. In some regions, the selection of winter cover crops and forage legumes may be effected, since they can serve as host plants. It appears that soybean rust losses will be covered by multiple peril crop insurance (MPCI), which covers a wide range of damages caused by weather, pests, and other natural causes. The Risk Management Agency (RMA) of the USDA states: "[L]osses to soybean production due to soybean rust disease is an insurable cause of loss provided the insured can verify that the cause was natural and available control measures were properly applied. If there are no effective control measures available or there are insufficient amounts of chemicals available for effective control, resulting loss of production would be covered. It will not be a covered loss if there are sufficient control measures available, but the insured elects not to use them. Policyholders who are certified as organic soybean producers would not have to follow any non-organic cultural practices." For the complete text of the RMA statement, visit the RMA Web site. Asian Soybean Rust (ASR) and Organic ProductionOrganic soybean production and soyfoods processing is a multi-billion dollar industry. There were appoximately 200,000 acres of certified organic soybeans produced in the U.S. in 2001, according to USDA Economic Research Service. In 2004, an ad-hoc network was formed to address Asian soybean rust in organic soybean production. It was facilitated by USDA Office of Pest Management Policy (contact Ted Rogers at trogers@ars.usda.gov), and comprised of personnel from USDA, agricultural researchers, organic farmers, representatives from the soybean and soyfoods industries, pest control registrants, and non-governmental organizations. A primary step was the identification of organically approved plant-disease control products with potential for soybean rust control. The target pest-control products were selected from the Organic Materials Review Institute (OMRI) Brand Name Products List. OMRI is a non-profit organization that evaluates crop and livestock production inputs in certified organic production. These include soil and foliar fertilizers, biostimulants, livestock feeds, and insect, weed, and disease controls. Product manufacturers submit technical documentation—including proprietary product ingredients—and OMRI assures that the ingredients and formulations match the standards set forth by USDA's National Organic Program (NOP). The OMRI Brand Name Products List is a prominent resource for organic farmers. The OMRI Brand Name Products List is organized by Crop, Livestock, and Processing categories. It can be sorted by Generic Category or Product Brand Name. It also provides complete Company Contact Information. All of these OMRI documents are available on the Web. The ad-hoc network developed plans for screening organically approved disease-control products to determine their efficacy against soybean rust. The field trials will be conducted in collaboration with researchers in South Africa and South America. Their summer growing season (south of the equator) is our winter season. However, these trials have not yet been conducted, and no data is currently available. Current Research on Organic Methods to Control Asian Soybean Rust (ASR)Researchers at Iowa State University stated they will test all organically approved materials (copper, sulfur, hydrogen peroxide, and other naturally based materials) for efficacy against ASR in 2005. Dr. Kathleen Delate, coordinator of ISU's organics program, explained that the field trails will be conducted in cooperation with southern states where the disease has already been detected. A research collaborative involving Iowa State University, Michigan State University, University of Florida, and the Rodale Institute was formed to seek research funds for control of ASR in organic soybean production. The USDA's Integrated Organic Program awarded $480,000 to the collaborative in August 2005, enabling the multi-institutional research project to proceed. Organically Acceptable Products and Practices That May Control Asian Soybean Rust (ASR)AgraQuest, the biocontrol company best known for its Serenade® biofungicide based on Bacillus subtilis (QST 713 strain), has released a new formulation known as Ballad® biofungicide—based on Bacillus pumilus (QST 2808 strain)—that is labeled for control of ASR in organic soybeans. AgraQuest announced that field trials in Africa and South America showed Ballad is effective against ASR. Ballad is available for sale to U.S. soybean growers. For detailed production information, visit AgraQuest's Web site. Mr. Reg Destree, a commercial vegetable grower from La Crosse, Wisconsin, who serves as a consultant for the Dramm Company's organic fertilizer division, has published a series of leaflets on use of fish fertilizers in combination with other natural ingredients (e.g., fish hydrosylate, neem oil, karanja oil, insecticidal soap, microbial-mineral blends). These soil- and foliar-applied liquid sprays are intended for insect and disease suppression, in addition to supplying fertility and boosting plant health. The Web site for Drammatic® Liquid Fish Plant Food has about a dozen leaflets with detailed liquid organic fertilization recipes. Mr. Destree is distributing a new leaflet, 2005 Plant Pathogens—Asian Soybean Rust, in response to the Asian soybean rust threat to organic soybean growers. However, it is not yet available on-line. ATTRA can provide a print copy of Mr. Destree's leaflet (above) on request. Contact: Modern crop breeding programs commonly employ genetic engineering techniques. When rust-resistant soybean varieties do emerge, they may contain GMO (genetically modified organism) germplasm. Since GMO crops are not allowed in organic production, organic farmers should verify GMO-free status of new rust-resistant soybean varieties. Crop rotations are a traditional disease control strategy in organic farming, and they are especially helpful in the control of soil-borne diseases. However, soybean rust is wind-borne and descends in clouds of spores across the countryside. Research has shown that a traditional crop rotation of corn and soybeans offers no disease control benefits.(Suderman, 2004) Compost teas, microbial inoculants, and foliar biostimulants are natural biological control strategies attracting attention for their disease suppressive characteristics. Compost teas and microbial inoculants contain a diversity of microorganisms that help regulate soil fertility, boost crop health, and compete with plant pathogenic organisms for food resources in the rhizosphere (root zone) and the phyllosphere (leaf zone). The physiological mechanisms for natural biological control include general suppression, specific suppression, antagonism, competition, induced resistance, and related mechanisms that suppress the ability of plant pathogenic organisms to cause infection. However, no research data is available to confirm efficacy of these natural approaches for Asian soybean rust. EM (Effective Microorganisms) is one of several microbial inoculants being explored for control of Asian soybean rust. Of particular interest are the advanced recipes known as EM-Fermented Plant Extracts and EM-5, which are specifically geared to insect and disease suppression. ATTRA can provide resources on compost teas and EM (Effective Microorganisms), including the advanced recipes for EM-FPE and EM-5, on request. Foliar fertilization with a blend of organic fertilizers, minerals, and biostimulants (e.g., fish hydrosylate, seaweed, calcium, humic acid, etc.) is known to boost crop health, and foliar sprays are commonly employed in organic farming. There is a growing trend in eco-farming to monitor plant tissue sap for Brix, pH, and EC, using specialized hand-held pocket meters. This data is used as an indicator of crop nutritional status to guide development of specialized foliar blends and spray applications. One chart that has attracted attention suggests that pH of plant sap functions as an indicator of plant susceptibility to insect and disease attack; higher (alkaline) pH is said to increase probability of insect attack, while lower (acidic) pH is said to increase probability of disease attack. Brazilian farmers use on-farm sentinel plots of highly susceptible soybean cultivars, sowed early, to provide an early detection monitoring system for ASR. Brazilian growers have also had some success in control of ASR by eliminating volunteer soybeans and naturalized kudzu, planting early maturing soybean varieties (so young plants emerge when rust spores are low in number), shortening the planting period (later-planted fields can sometimes get rust from earlier-planted fields), and rotating soybeans with another crop. Jose Luiz Moreira Garcia, an organic farmer and eco-farming advisor in Brazil, published "Dealing with Asian Soybean Rust Naturally" on the SANET e-mail discussion list on March 12, 2005. He described the life cycle of ASR, emphasizing that it affects soybean plants after they have flowered, reducing seed size and yield by 50%. Garcia discounted the ability of compost teas to reduce soybean rust infection, at least as a stand-alone treatment. Instead, Garcia emphasized the use of potassium-silicate fertilizers, humates, sulfur, boron, and copper for Asian soybean rust control in organic production. Garcia's post can be viewed in the SANET archives. Dr. Philip Wheeler, an eco-farming advisor with Crop Services International, published "How to Deal with Soybean Rust & Aphid" in the June 2005 issue of Acres U.S.A. magazine. Drawing upon Jose Garcia's experience in Brazil, Wheeler emphasized the use of soluble silica fertilizers. However, he notes that silicate fertilizers are not approved for organic production under the USDA-NOP. Organic sources of silica include rock powders and Biodynamic (BD) methods, including the BD Preparations No. 501 and No. 508, BD homeopathics, and energetic field broadcasters. Wheeler emphasizes the use of boron and calcium mineral supplements, as well. Article reprints are available through Acres U.S.A. Implications of Asian Soybean Rust (ASR) for Organic Soybean Production in the U.S.It is difficult to assess the implications of ASR for organic production. One result is that producers in the southern states may shift out of soybeans in the near future. Some organic buyers are increasing their contracts for soybeans in Minnesota and North Dakota because of the lower threat of rust in regions further north and further west. Ron Rosmann, an organic grower in Harlan, Iowa, said, "At our farm, we're taking some steps to plan ahead for the possible arrival of soybean rust. We will be planting fewer acres of organic soybeans this next year, mostly because that is how it works out with our rotation sequence. We also intend to plant a new alternative organic crop, flax. The net profit for flax appears to be very competitive with organic soybeans and we are excited about the possibility of adding a new crop to our rotation."(Duffy, 2004) Should the Animal and Plant Health Inspection Service (APHIS) require spraying organic crops with unapproved fungicides, the immediate crop would lose organic certification, but the land would not be decertified per NOP 205.672. It is not likely that APHIS would do so, but individual states may require spraying. ReferencesDuffy, Mike. 2004. Science behind The News: Looking at Asian soybean rust. Leopold Letter. Vol. 16, No. 4. p. 5. www.leopold.iastate.edu/pubs/nwl/2004/2004-4-leoletter/rust.htm#duffy Johnson, Andrea. 2004. Early soybean rust resistant breeding material may become available. Farm and Ranch Guide. December 22. www.farmandranchguide.com/articles/2004/12/22/ag_news/production_news/prod04.txt Suderman, Arlan. 2004. Rust swells uncertainty. Wallaces Farmer. December. p. 4. Yang, X.B., E.M. Del Ponte, and A.P. Dias. 2004. Knowing the risk of soybean rust by comparison with Brazil. Iowa State University Department of Plant Pathology. www.plantpath.iastate.edu/soybeanrust/taxonomy/term/5 ResourcesBibliographical Resource List on Soybean RustSoybean Rust: A National Agricultural Library Resource Guide Key Sources of Information on Soybean RustUSDA Soybean Rust Information Site USDA Public Soybean Rust Website Asian Soybean Rust: Identifying, Confirming, and Managing Asian Soybean Rust Soybean Rust—A Real Threat to American Agriculture Soybean Rust (Phakopsora pachyrhizi) Soybean Rust—Hot Issues Soybean Rust Plant Management Network: Soybean Rust Soybean Rust Economic Assessment Management Considerations for Asian Soybean Rust: Three Basic Pillars of Control Soybean Rust: Is the U.S. Soybean Crop At Risk? Asian Soybean Rust Tabloid Ohio Soybean Rust Guidelines Organic Updates on Soybean RustResearchers Responding to Discovery of Soybean Rust in the U.S. Soybean Rust Update for Organic Farmers
By Holly Born and Steve Diver The ATTRA Project is operated by the National Center for Appropriate Technology under a grant from the Rural Business-Cooperative Service, U.S. Department of Agriculture. These organizations do not recommend or endorse products, companies, or individuals.
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