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Soybean Production in Mississippi

Asian Soybean Rust: Frequently asked questions

 

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What is the risk of having soybean rust in soybean fields in Mississippi in 2010?

This will all depend on the weather early in the season and amount of overwintering that occurs in southern locations.  Based on cold temperatures during late 2009 and early 2010 observations on kudzu from AL, FL, GA, LA, and MS suggest that no rust survived the winter.  Just because a particular field had soybean rust in 2009 doesn’t mean that it will have soybean rust in 2010.  In general, based on past experiences, risk will be low to medium for early planted soybeans, for later planted soybeans the risk will be medium to high.  Typically, the inoculum potential will be lowest early in the season.

How will we prevent damage from soybean rust if it occurs in 2010?

Preventative applications of effective fungicides properly timed will prevent yield losses due to soybean rust.  Producers should consider applying an R3/R4 fungicide application as a means of potentially preventing yield loss due to the disease.  While a fungicide application at this particular growth stage will not provide protection for the rest of the growing season it may delay infection from the SBR causal fungus.

Should I grow soybeans with the threat of soybean rust in 2010?

2010 will be our sixth full year with a potential rust threat in MS.  In the past three years we have effectively managed the rust threat through the use of fungicide suggestions created by monitoring sentinel plots, and using the identification of rust to aid us in developing a preventative program for MS producers.  Additionally, check for updated management information on the soybean rust hotline (1-866-641-1847).  This is a FREE telephone call and is updated as often as is necessary.  Plans should not be altered due to the potential for rust. Rust can be prevented through the use of effective fungicides.

What is the origin of soybean rust and how did it spread to Mississippi?

Soybean rust was first found in 1902 in Japan and has moved throughout all soybean growing areas of the world by windblown spores.  The fungus cannot survive in the absence of a host so it likely must blow into our production area on an annual basis.

How long does it require from the time the spore lands on a leaf until it can sporulate again?

Generally 7-14 days is required from the time a spore lands on a leaf, leads to infection, produces a pustule, and begins to sporulate.  Additionally, the majority of this will depend on the environmental conditions (temperature, cloud cover, relative humidity) present at the time the spore lands on the leaf.

What is the developmental cycle of soybean rust?

Spores are disseminated by wind currents and land on leaves.  If environmental conditions are favorable, the spores germinate and directly penetrate the plant tissue.  Within 6-7 days a pustule begins to develop and urediniospores begin forming and are released in 2-3 days.  Pustules can discharge spores for 2-3 weeks thus rapidly spreading this disease to other plants within a field or to distant soybean fields depending upon wind currents.

 

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Do any soybean varieties have resistance to soybean rust?

No commercially available varieties carry resistance to soybean rust.

What fungicides will be available for prevention of this disease?

Please refer to the fungicide table included.  In addition to the products included in this list there are some possible fungicide combinations.

What is the estimated cost for control of soybean rust?

It is estimated the cost of fungicides will range from a low of $8 to approximately $14 per acre per application not including application costs.

How will producers offset the additional cost for fungicides to maintain profitable soybean production?

Fungicide use will typically increase soybean yields even in the absence of rust (a 12 year study in Mississippi indicates a 3.3-5.9 bu/A average increase from only 1 carefully timed fungicide application in those situations where soybeans follow soybeans) if the fungicide is applied to high-yield potential irrigated soybeans in a continuous soybean program.

How many applications of fungicides will be required to control rust and at what stages of plant growth should these fungicides be applied?

The number of applications may range from 0 to 3 (depending upon inoculum levels, environmental conditions, and how early in the growing season the initial infection occurs) and should be applied depending upon the presence of rust in the U.S., crop stage when rust is discovered, and the specific recommendations of MSU Extension Service personnel that are actively scouting for rust throughout MS.  Should you have specific questions please call your local county extension office.  For up to date information refer to the commentary on the public website (www.sbrusa.net) and also the MS Soybean Rust Hotline (866-641-1847) that is sponsored in part by the Mississippi Soybean Promotion Board and BASF.

Will combinations of fungicides provide better control of soybean rust?

Soybean rust prevention can be attained with a single fungicide, or a combination of fungicides if timing, rate, and proper coverage are attained. To prevent the possible development of resistance, rotate mode of actions and specific product chemistry for each application.

 

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What water volume will be recommended for air and ground application?

Air- 5 GPA Ground- 15 GPA

Will control be improved by adding crop oil concentrate (COC) if so at what rate?

COC and adjuvants may aid in better coverage and canopy penetration. The rate may vary according to the situation.  Refer to the fungicide label for specific information on whether or not a COC or adjuvant is necessary in your particular situation.

What fungicide combinations and rates will be considered an effective program?

Triazole and strobulurin fungicides will provide effective prevention of rust. See the “control” page for the specific products, rates, and any other pertinent information regarding the use limitations.

Will management of this disease be different when growing Group IV vs. Group V soybean varieties?

Yes, early maturity, early planted soybeans should have less risk than later maturity, late planted soybeans or soybeans planted behind wheat.

Should I be purchasing fungicide now after new labels are approved in preparation in event there is a shortage for next season?

There is still uncertainty regarding if or when soybean rust may appear this season, therefore, 1 application of a strobulurin could be purchased and could be used even if soybean rust did not appear during the 2010 growing season. Studies have shown the advantages of a fungicide application even in the absence of rust.

How will the rust prevention fungicide program affect other diseases that normally occur each season on soybeans?

Effective prevention of late season soybean diseases will be obtained with the strobulurin fungicides if used at R-3 to R-4 growth stages. While triazole fungicides are very effective for the prevention of rust, they have poor prevention of most late season diseases.

 

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How does soybean rust over winter and reinfect soybeans the next season?

The soybean rust fungus is believed to over winter in southern Florida, southern Texas and the Caribbean, however, we do not have specific information on the survival of the fungus.  It is also possible that the fungus survives in the living tissue of other, yet unknown, host plants.

Are seedling soybeans affected by rust and what stages are more susceptible to severe damage?

The cotyledons of seedling soybean plants can be infected, but they fall off the plant quickly. Soybeans are most susceptible at bloom (R1) and later stages.  However, in 2008 rust was observed in volunteer soybeans on the edge of a heavily infected soybean field.  This suggests that an excessive amount of inoculum needs to be present for this type of infection to occur.

Does rotation with non host crops reduce losses from soybean rust?

No because it is a wind blown pathogen and typically has moved from south to north.

Will soybean rust reoccur in the same field where it was found the previous year?

The presence of rust in any one field has nothing to do with its reoccurrence in the same field or surrounding fields in subsequent years.  This has also been the case in the particular counties that have tested positive for soybean rust.  The appearance of rust in any one particular location will depend on where the first infections occur with the United States this season.  Infection of the MS soybean crop will also depend on prevailing wind currents to carry the spores into our state. 

Will a cold winter kill the fungus?

Cold weather alone will not kill the rust fungus. Rust spores can survive up to 52 days in the absence of a host.

How long before a resistant variety can be made available?

A resistant variety may not be available until 2011 or 2012.  Tolerance to the fungus has been identified in both South American and North American breeding studies.

Can some fungicides be applied as curative applications after rust is found in a field?

Rust control with fungicides is all preventative. Fungicides must be applied before soybean rust becomes established in a field of soybeans. Major losses can be prevented after rust has been located in a particular field (if less than 10% infected leaves) with a triazole fungicide.  However, it should be noted, that detecting this level of rust in any soybean field is difficult.

 

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Will planting date affect rust development and the number of applications of fungicides that will have to be applied?

Early planting should reduce losses from rust and the number of applications of fungicides.  Our recent past has shown us that later planted soybeans may in fact be at more risk to infection from soybean rust.

Will an application of fungicide have to be applied at the R1 stage in 2010, if not how will the timing of the application be determined?

Depending on when rust is detected in 2010, this will determine if an R1 application is necessary. Early planted sentinel plots will help in determining if a fungicide is necessary.

Can a soybean field on a soybean producer's farm serve as a sentinel plot?

Yes, if planted much earlier than the remainder of the soybeans to be grown on the farm. However, if planting later the sentinel plots established by the Extension Service may provide more advanced information.  In 2010 we added two sentinel plot locations along the coast, one in Biloxi, and one in Bay St. Louis.  In general, sentinel plots are placed in strategic locations so we can create reliable data to help us build a particular suggestion if and when rust arrives.

If fungicides are used in rust prevention will some loss in yield occur?

Yes, yield losses are possible, but losses should be minimal if fungicides are applied timely and with good coverage.  However, this depends on the level of rust within individual fields and also the amount of inoculum within MS.  In 2009, we estimated the amount of statewide yield loss from soybean rust to be between 0 and 3%; however, this was greatly overshadowed by the amount of seed rot that occurred following several weeks of wet weather.  Rust as detected earlier in the major soybean growing areas within MS than in the past.  In addition, two particular fields in Noxubee County suffered between 8 and 25% yield loss in response to soybean rust infection.

Will soybean rust have the potential for causing heavy damage every year?

It has the potential, but losses will vary from year to year depending on the presence of inoculum, environmental conditions, and if effective fungicides have been used as suggested.

How will producers be informed on what, when and how to prevent rust?

Information will be provided through county Extension offices, e-mail lists, DTN, Internet sites (in particular www.sbrusa.net), publications, meetings, radio, T.V., and the MS Soybean Rust Hotline (866-641-1847) and all other methods of information dissemination.

What will be the role of field scouting in management of rust?

Weekly scouting of sentinel plots will serve as an early alert mechanism, field scouting will insure proper timing of the fungicides and other pest problems that may need management at the same time as fungicide applications.

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