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APPROPRIATETECHNOLOGYTRANSFERFORRURALAREAS

www.attra.ncat.org

ATTRA is the national sustainable agriculture information center operated by the National Center for AppropriateTechnology under a grant from the Rural Business-Cooperative Service, U.S. Department of Agriculture. Theseorganizations do not recommend or endorse products, companies, or individuals. ATTRA is located in theOzark Mountains at the University of Arkansas in Fayetteville (P.O. Box 3657, Fayetteville, AR 72702). ATTRAstaff members prefer to receive requests for information about sustainable agriculture via the toll-free number

800-346-9140.

By George KuepperNCAT Agriculture Specialist

December 2001

AGRONOMYTECHNICALNOTE

AbstractWhite mold has become a serious pest in commercial soybean productionespecially whereintensive production techniques are used. This publication discusses the various non-chemicaloptions for addressing the problem, including varietal selection, canopy management, delayedplanting, crop rotation, tillage reduction, and biofungicides.

ORGANICCONTROLOFWHITEMOLD

ONSOYBEANS

How White Mold Becamea Problem

White mold, also known as sclerotinia stemrot, is caused by the fungus Sclerotiniasclerotiorum. It appears as fluffy white mycelialgrowth, most prominently on the stems. Theorganism begins its lifecycle whensclerotiafungal structures capable of

surviving winter

germinate on the soilsurface, forming mushroom-like growths.These mushrooms eject microscopic spores.When spores land on soybean flower petals,they promptly germinate and colonizationbeginsprogressing from the pods to thestems, destroying those plant structuresprematurely. The disease may also spreadfurther from inter-plant infection. Finally, anew generation of sclerotia are formed on theinfected plant tissue; these pass through thecombine and are returned to the soil surface.

Some sclerotia are harvested with the beansand may be spread further through thehauling, cleaning, and storage processes (1).

White mold is heavily influenced by weatherand microclimatic conditions. Progress of the

disease is favored by below-average airtemperatures, high relative humidity, and soilmoisture. When these conditions occur duringthe two weeks prior to peak flower on thelower stems, the disease incidence can beespecially severe (1). However, the fact thatwhite mold has gotten more severe in recentyears has more to do with how soybeans arebeing grown.

Growers have been increasing soybean acreageand managing for higher yield levels. Many ofthe practices associated with these trendsshorter rotations, narrower rows, earlierplantingcreate a less healthy environmentthat favors white mold development (2).

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A number of techniques and strategies formanaging white mold have been identified.Because white mold is proving so damaging tosoybean yields, growers are encouraged toaddress the problem on several fronts, ratherthan settling on a single control measure.

Varietal Selection

Choosing soybean varieties that demonstrate adegree of tolerance or resistance to white moldis considered the first and principal steptoward managing the disease. At the sametime, the use of specific cultural practices canreduce the risk of infection and offer moreflexibility in varietal selection. Varieties arecommonly divided into four categories of

disease reaction (3):

Moderat el y Resi st ant. This is currentlythe highest form of genetic resistanceavailable in soybeans. Moderatelyresistant varieties may exhibit 1025%mortality in the field, but will still producean acceptable economic yield. When usedin rotation, these varieties will reduceoverwintering sclerotia in the soil.

Tolerant. Since plant mortality can reach

as high as 26

50%, tolerant varieties shouldbe used only where, because of field historyand other management strategies, the riskof infection is moderate to low. Yieldsunder these conditions are expected to beeconomically acceptable. Tolerantvarieties, if infected, may increaseoverwintering sclerotia that can infectsubsequent crops.

Susceptible. Unless the risk of infection isvery low, susceptible varieties are likely to

produce unacceptable yields.

Highly Suscept i ble. Highly susceptiblevarieties should be avoided when even theslightest risk of white mold exists.

Local Cooperative Extension and seedsuppliers will have good information on thespecific white-mold-tolerant varieties that aresuitable for your region and for specificcultural conditions.

Canopy Management

Current wisdom encourages the use of narrowrow spacing for soybeans to increase yieldsand enhance weed suppression through adense, quickly closing canopy. Unfortunately,an early, dense crop canopy creates anenvironment friendly to white mold fungus.Dense planting strategiesaccomplishedeither through the use of narrow rows orsimply by increasing the seeding raterequirethe use of moderately resistant varieties, unlessthere is no history of the disease on the fieldsite (1).

Fertility & Planting Date

Early planting of soybeans provides for alonger growing season and increases thechance for higher yields. Unfortunately, it alsoincreases the overlap time between soybeanflowering and the release of white moldspores. For this reason, delayed planting canreduce disease incidence. Fertilizationpractices, especially the use of nitrogen-richmanures and fertilizers, can worsen whitemold incidence by stimulating early, lushcanopy growth (1).

Crop Rotation

White mold sclerotia are moderately long-livedin the soil. It is virtually impossible toeliminate them as long as host crops areplanted at intervals of five years or less. Whitemold has a fairly wide host range that includesall beans, peas, sunflower, canola, cole crops,and carrots. Alfalfa is also a host crop (butapparently a poor one). Some non-host cropssuitable for rotation include corn, small grains,

and all grass crops.

While long rotations to non-host crops may notbe feasible, research has demonstrated thatshorter two- or three-year rotations to non-hostcrops are still highly effective in reducingsclerotia in the soil and should be seriouslyconsidered as part of any overall diseasemanagement strategy (1).University ofWisconsin plant pathologist Craig Grauspecifically recommends a rotation of

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cornsoybeanssmall grains (in that specificorder)using either oats, wheat, or barley asthe small grain crop(2).

Reduced Tillage

While deep plowing may bury the sclerotiaafter a bad season, repeated plowing andother conventional tillage operationseventually distribute long-lived sclerotiathroughout the plow zone, while still leavingplenty on the soil surface to germinate eachseason. Research from Wisconsin hasdemonstrated that white mold incidence canactually be reduced under no-till cultivation.While the sclerotia in no-till fields all remainon the soil surface where they could germinate

next year, they are also fully exposed toweathering and decay. This situation reducesthe population considerably (1).

Unfortunately, no-till strategies for organicproduction are still largely in the early stagesof development. (Ask for the ATTRApublication Pursuing Conservation TillageSystems for Organic Crop Productionfor moredetails.) Since some cultivation is still likelyunder organic management, growers areencouraged to explore minimum-tillageoptions as these tend to keep the diseaseconfined to patches rather than spreading itthroughout the field(2).

Weed Control

Good weed control can also reduce white moldincidence. Several common weed speciesincluding lambsquarter, common ragweed,red-root pigweed, and velvet leafarealternate hosts for white mold. As a result,their presence in soybeans, in rotation crops,and on field borders can help to maintain aready population of sclerotia for future cropinfection. Sudden outbreaks of white mold insoybean fields that were previously mono-cropped to continuous corn have beenexplained by the presence of weed hosts(1).

Alternative Fungicides

Since several fungal organisms prey on whitemold in crop fields (4),there are goodprospects for the development of biofungicidesas a tool for white mold management. Themost consistently effective of the predatoryorganisms evaluated has been Coniothyriumminitans. At least one commercial field-cropformulation of C. minitansis now on the marketunder the trade name Contans(5). Contansis manufactured by the German companyProphyta. Prophytas distribution agent in theU.S. is Encore Technologies (6),which can becontacted for more details on availability andclearance of Contans for specific crop use.

There do not appear to be any current

recommendations for the use of sulfur- orcopper-based fungicides for white moldmanagement in soybeans. One traditional texton disease management (7)did suggest thatthere might be some efficacy from their use.Unless a product is clearly labeled for a specificuse, however, growers are advised to contactCooperative Extension and the productmanufacturer before experimenting on acommercial crop.

Summary

White mold can be a serious disease problemin commercial soybeans; its management hasbecome a major consideration. The drive forhigher yields has been a chief factor in makingwhite mold such a serious problem. Culturalpractices like delayed planting, wider rows,lower seeding rates, and avoiding excess Nfertilization can reverse this trend but maysacrifice per-acre yields. Longer crop rotationsmay reduce annual soybean acreage, but canintroduce greater diversity and stability to the

farm system.

At present, varietal selection is the foundationfor most white mold managementplansespecially those that continue toemploy high-yield production practices thatfavor the disease. The choice of a cultivarshould be based on the risk of infectiona

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factor influenced by weather conditions,cultural practices, and field history.

References:

1) Grau, Craig. 1998. White mold of soybean.

University of WisconsinCooperativeExtension. .

2) Gallepp, George. 1988. Keys to white moldcontrol. Farmers Digest. AugustSeptember.p. 14.

3) Grau, Craig, Edward S. Oplinger, and JamesE. Kurle. 1998. White mold in soybean:Soybean variety selection. University ofWisconsin Cooperative Extension, Madison,WI. .

4) Agrios, George. 1988. Plant Pathology, 3rd

edition. Academic Press, New York, NY.p. 430431.

5) Fravel, Deborah. 1999. Commercialbiocontrol products for use against soilbornecrop diseases. United States Department ofAgriculture, Beltsville, MD. January 1..

6) Encore Technologies, LLC111 Cheshire Lane, Ste. 500

Minnetonka, MN 55305612-404-9596E-mail:billstoneman@home.comhttp://www.encoretechllc.com

7) Westcott, Cynthia. 1971. Plant DiseaseHandbook, 3rdedition. Van NostrandReinhold Co., New York, NY. p. 351353.

Additional Resources:

Diver, Steve. 1998. Compost Teas for PlantDisease Control. ATTRA Pest Management

Technical Note.While not discussed as an alternativecontrol option in the textthe author isunaware of any compost tea trials for whitemold controlsuch materials might beefficacious and could be worthinvestigating. Particularly relevant to thisis a discussion of protective biofilmsfeatured on the Soil Foodweb Inc. website at.

Brunoehler, Ron. 1999. Put white mold onhold: Researchers identify resistant varieties.Soybean Digest. April. p. 34.

Features a short list of 26 varieties with whitemold resistance ratings observed over twoseasons.

Larson, E. Anne and John VanDyk. 1999.Biological control against white mold. IowaState University, Ames, IA. July 12..

Lundeen, Peter and X.B. Yang. 1998. Soybeanwhite mold. Iowa State University, Ames, IA.May 29. .

North Central Soybean Research Program.2001. White Mold Coalition Website. .

North Dakota State Department of PlantPathology. 1998. Proceedings of theSclerotinia Workshop: A Minnesota/NorthDakota In-Service Extension Workshop.January 21. .

Uphoff, Michael, X.B. Yang, and John VanDyk.1999. Tolerance results to white mold and SDS.Iowa State University, Ames, IA. November 3..

Williams, Greg and Pat Williams. 2001. Wormcastings for fungus control. HortIdeas. May.p. 56.

By George Kuepper

NCAT Agriculture Specialist

December 2001

The Electronic version of Organic Control ofWhite Mold on Soybeansis located at:

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PDFhttp://www.attra.org/attra-pub/PDF/whitmold.pdf

http://plantpath.wisc.edu/~soyhome.pp/http://plantpath.wisc.edu/~soyhome.pp/http://www.barc.usda.gov/psi/bpdl/bioprod.htm#Contanshttp://www.barc.usda.gov/psi/bpdl/bioprod.htm#Contansmailto:billstoneman@home.comhttp://www.encoretechllc.com/http://www.soilfoodweb.com/leaf.htmlhttp://www.ipm.iastate.edu/ipm/icm/1998/11-9-1998/biocontrolwm.htmlhttp://www.ipm.iastate.edu/ipm/icm/1998/11-9-1998/biocontrolwm.htmlhttp://www.exnet.iastate.edu/Pages/plantpath/whitemold/whtmld.htmlhttp://www.exnet.iastate.edu/Pages/plantpath/whitemold/whtmld.htmlhttp://www.ncsrp.com/whitemold/http://www.ncsrp.com/whitemold/http://www.ndsu.nodak.edu/plantpath/sclero.htmhttp://www.ndsu.nodak.edu/plantpath/sclero.htmhttp://www.ipm.iastate.edu/ipm/icm/1999/11-8-1999/wmsdstolres.htmlhttp://www.ipm.iastate.edu/ipm/icm/1999/11-8-1999/wmsdstolres.htmlmailto:georgek@ncatark.uark.eduhttp://www.attra.org/attra-pub/whitemold.htmlhttp://www.attra.org/attra-pub/PDF/whitmold.pdfhttp://www.attra.org/attra-pub/PDF/whitmold.pdfhttp://www.attra.org/attra-pub/whitemold.htmlmailto:georgek@ncatark.uark.eduhttp://www.ipm.iastate.edu/ipm/icm/1999/11-8-1999/wmsdstolres.htmlhttp://www.ipm.iastate.edu/ipm/icm/1999/11-8-1999/wmsdstolres.htmlhttp://www.ndsu.nodak.edu/plantpath/sclero.htmhttp://www.ndsu.nodak.edu/plantpath/sclero.htmhttp://www.ncsrp.com/whitemold/http://www.ncsrp.com/whitemold/http://www.exnet.iastate.edu/Pages/plantpath/whitemold/whtmld.htmlhttp://www.exnet.iastate.edu/Pages/plantpath/whitemold/whtmld.htmlhttp://www.ipm.iastate.edu/ipm/icm/1998/11-9-1998/biocontrolwm.htmlhttp://www.ipm.iastate.edu/ipm/icm/1998/11-9-1998/biocontrolwm.htmlhttp://www.soilfoodweb.com/leaf.htmlhttp://www.encoretechllc.com/mailto:billstoneman@home.comhttp://www.barc.usda.gov/psi/bpdl/bioprod.htm#Contanshttp://www.barc.usda.gov/psi/bpdl/bioprod.htm#Contanshttp://plantpath.wisc.edu/~soyhome.pp/http://plantpath.wisc.edu/~soyhome.pp/