CORN Newsletter: 2004-03, February 4, 2004

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C.O.R.N Newsletter 2004-03
February 4, 2004 - February 18, 2004

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Soybean Rust – What are the risks for 2004?
by Anne Dorrance


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I have been asked on a number of occasions what the risks will be for soybean rust during this next growing season. I don’t mean to be curt – but this really does depend on which way the winds blow. Let me explain, Soybean rust is a fungus, very similar to the rust fungi that cause wheat leaf rust and corn leaf rust. There are two species of soybean rust, one is a mild strain known as Phakopsora meiombae and the more aggressive strain, Phakopsora pachyrhizi. P. pachyrhizi is the species that as gotten all of the attention. It has quickly moved from its place of origin in southeast China in to Africa then to South America. In South America, it first arrived in Paraguay during 2001 – and from there it has been confirmed in all of the soybean regions in Brazil with reports from northern Argentina. Yield losses in South America ranged all over the board – Speculation on potential yield losses in the US ranged from as high 50% or more. Rust will change the way we produce soybeans – when it gets here.

Four routes have been proposed for soybean rust to reach the US.

Via the Central American land bridge—This rust has a broad host range – so conceivably it could infect and colonize hosts all through central America to reach the US. This would take awhile and is dependent on the fact that there are hosts all the way through central America.

On the winds of a hurricane. Conceivably a storm could pick up lots of rust spores from production fields in northern Brazil and carry these across the Caribbean and drop spores on winter nurseries in Southern Florida or on the Kudzu that grows through out the South. Once the rust is established here, then with spring and summer storms it would track via the rust pathway that we are familiar with for both corn and wheat. There are no reports of this happening (February 2, 2004). Of all of the possible outcomes – this may have the highest probability. This is also the easiest for us to implement management strategies – because we already have recommendations and procedures in place for wheat and corn – they would only need to be tweaked for soybeans.

Spores that survive in debris in shipments of seed or meal. Residue or debris is that is left near production fields were the spores could infect soybean plants. This is questionable. We know from corn and wheat rust fungi that the spores do not survive and serve as inoculum sources in or on seed. The debris is buried with the seed or spores are no longer alive from the time of harvest to planting season. We can take additional precautions here, bury debris from containers away from production fields, and monitor fields that are close to ports or facilities were seed cleaning may take place.

Bioterrisom – this is the big unknown. However, on a practical level, I also think this is unlikely, it is very difficult to get successful infections with many fungi by just spreading them onto plants, there are very specific environmental parameters that have to be met in order for such an attack to be successful.

So what should growers do this year to be ready for soybean rust. Really not much. It is not here yet, when it does arrive, we will manage it, successfully with fungicides. Timing of applications as well as efficacy of material will be very important to this success. Two materials are currently registered for soybean rust in the US. Section 18 requests for 6 additional materials have been applied for. Once approved, we will begin the make application to include Ohio on these labels. After that time, we can make some sound recommendations based on the efficacy trials that USDA is conducting in Brazil and Paraguay. Product costs and projected yields will also play a role in these recommendations.

For 2004, we should be vigilante in scouting and watching our fields for unusual leaf spots or large numbers of leaf spots. I do not think it is wise to stockpile fungicides. Efficacy, cost, and timing are all data that you will want before making a wise decision to managing this pathogen and BEFORE you make that financial investment. But, knowing how much Round-up is sprayed in this state over such a sort period of time, I am highly confident that Ohio producers and custom applicators are up to the task to make fungicide application should they become necessary.

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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