ORGANIC CONTROL OF WHITE MOLD ON SOYBEANS AGRONOMY TECHNICAL NOTEAPPROPRIATE TECHNOLOGY TRANSFER FOR RURAL AREAS www.attra.ncat.org Abstract White mold has become a serious pest in commercial soybean productionespecially where intensive production techniques are used. This publication discusses the various non-chemical options for addressing the problem, including varietal selection, canopy management, delayed planting, crop rotation, tillage reduction, and biofungicides.By George KuepperNCAT Agriculture SpecialistDecember 2001How White Mold Becamea ProblemWhite 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 ofsurviving wintergerminate on the soilsurface, forming mushroom-like growths.These “mushrooms” eject microscopic spores. disease is favored by below-average airWhen spores land on soybean flower petals, temperatures, high relative humidity, and soilthey promptly germinate and colonization moisture. When these conditions occur duringbeginsprogressing from the pods to the the two weeks prior to peak flower on thestems, destroying those plant structures lower stems, the disease incidence can beprematurely. The disease may also spread especially severe (1). However, the fact thatfurther from inter-plant infection. Finally, a white mold has gotten more severe in recentnew generation of sclerotia are formed on the years has more to do with how soybeans areinfected plant tissue; these pass through the being grown.combine and are returned to the soil surface.Some sclerotia are harvested with the beans Growers have been increasing soybean acreageand may be spread further through the and managing for higher yield levels. Many ofhauling, cleaning, and storage processes (1). the practices associated with these trends shorter rotations, narrower rows, earlierWhite mold is heavily influenced by weather plantingcreate a less healthy environmentand microclimatic conditions. Progress of the that favors white mold development (2).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 number800-346-9140.
A number of techniques and strategies for Canopy Managementmanaging white mold have been identified.Because white mold is proving so damaging to Current wisdom encourages the use of narrowsoybean yields, growers are encouraged to row spacing for soybeans to increase yieldsaddress the problem on several fronts, rather and enhance weed suppression through athan settling on a single control measure. dense, quickly closing canopy. Unfortunately, an early, dense crop canopy creates anVarietal Selection environment friendly to white mold fungus. Dense planting strategiesaccomplishedChoosing soybean varieties that demonstrate a either through the use of narrow rows ordegree of tolerance or resistance to white mold simply by increasing the seeding raterequireis considered the first and principal step the use of moderately resistant varieties, unlesstoward managing the disease. At the same there is no history of the disease on the fieldtime, the use of specific cultural practices can site (1).reduce the risk of infection and offer moreflexibility in varietal selection. Varieties are Fertility & Planting Datecommonly divided into four categories ofdisease reaction (3): Early planting of soybeans provides for a longer growing season and increases the• Moderately Resistant. This is currently chance for higher yields. Unfortunately, it also the highest form of genetic resistance increases the overlap time between soybean available in soybeans. Moderately flowering and the release of white mold resistant varieties may exhibit 10−25% spores. For this reason, delayed planting can mortality in the field, but will still produce reduce disease incidence. Fertilization an acceptable economic yield. When used practices, especially the use of nitrogen-rich in rotation, these varieties will reduce manures and fertilizers, can worsen white overwintering sclerotia in the soil. mold incidence by stimulating early, lush canopy growth (1).• Tolerant. Since plant mortality can reach as high as 26−50%, tolerant varieties should be used only where, because of field history Crop Rotation and other management strategies, the risk of infection is moderate to low. Yields White mold sclerotia are moderately long-lived under these conditions are expected to be in the soil. It is virtually impossible to economically acceptable. Tolerant eliminate them as long as host crops are varieties, if infected, may increase planted at intervals of five years or less. White overwintering sclerotia that can infect mold has a fairly wide host range that includes subsequent crops. all beans, peas, sunflower, canola, cole crops, and carrots. Alfalfa is also a host crop (but• Susceptible. Unless the risk of infection is apparently a poor one). Some non-host crops very low, susceptible varieties are likely to suitable for rotation include corn, small grains, produce unacceptable yields. and all grass crops.• Highly Susceptible. Highly susceptible While long rotations to non-host crops may not varieties should be avoided when even the be feasible, research has demonstrated that slightest risk of white mold exists. shorter two- or three-year rotations to non-host crops are still highly effective in reducingLocal Cooperative Extension and seed sclerotia in the soil and should be seriouslysuppliers will have good information on the considered as part of any overall diseasespecific white-mold-tolerant varieties that are management strategy (1). University ofsuitable for your region and for specific Wisconsin plant pathologist Craig Graucultural conditions. specifically recommends a rotation ofPAGE 2 //ORGANIC CONTROL OF WHITE MOLD ON SOYBEANS
corn→soybeans→small grains (in that specific Alternative Fungicidesorder)using either oats, wheat, or barley asthe small grain crop (2). Since several fungal organisms prey on white mold in crop fields (4), there are goodReduced Tillage prospects for the development of biofungicides as a tool for white mold management. TheWhile deep plowing may bury the sclerotia most consistently effective of the predatory organisms evaluated has been Coniothyriumafter a “bad” season, repeated plowing and minitans. At least one commercial field-cropother conventional tillage operations formulation of C. minitans is now on the marketeventually distribute long-lived sclerotia under the trade name Contans (5). Contansthroughout the plow zone, while still leaving is manufactured by the German companyplenty on the soil surface to germinate each Prophyta. Prophyta’s distribution agent in theseason. Research from Wisconsin has U.S. is Encore Technologies (6), which can bedemonstrated that white mold incidence can contacted for more details on availability andactually be reduced under no-till cultivation. clearance of Contans for specific crop use.While the sclerotia in no-till fields all remainon the soil surface where they could germinate There do not appear to be any currentnext year, they are also fully exposed to recommendations for the use of sulfur- orweathering and decay. This situation reduces copper-based fungicides for white moldthe population considerably (1). management in soybeans. One traditional text on disease management (7) did suggest thatUnfortunately, no-till strategies for organic there might be some efficacy from their use.production are still largely in the early stages Unless a product is clearly labeled for a specificof development. (Ask for the ATTRA use, however, growers are advised to contactpublication Pursuing Conservation Tillage Cooperative Extension and the product manufacturer before experimenting on aSystems for Organic Crop Production for more commercial crop.details.) Since some cultivation is still likelyunder organic management, growers areencouraged to explore minimum-tillage Summaryoptions as these tend to keep the disease White mold can be a serious disease problemconfined to patches rather than spreading it in commercial soybeans; its management hasthroughout the field (2). become a major consideration. The drive for higher yields has been a chief factor in makingWeed Control white mold such a serious problem. Cultural practices like delayed planting, wider rows,Good weed control can also reduce white mold lower seeding rates, and avoiding excess Nincidence. Several common weed species fertilization can reverse this trend but mayincluding lambsquarter, common ragweed, sacrifice per-acre yields. Longer crop rotationsred-root pigweed, and velvet leafare may reduce annual soybean acreage, but can introduce greater diversity and stability to thealternate hosts for white mold. As a result, farm system.their presence in soybeans, in rotation crops,and on field borders can help to maintain a At present, varietal selection is the foundationready population of sclerotia for future crop for most white mold managementinfection. Sudden outbreaks of white mold in plansespecially those that continue tosoybean fields that were previously mono- employ high-yield production practices thatcropped to continuous corn have been favor the disease. The choice of a cultivarexplained by the presence of weed hosts (1). should be based on the risk of infectiona //ORGANIC CONTROL OF WHITE MOLD ON SOYBEANS PAGE 3
factor influenced by weather conditions, Brunoehler, Ron. 1999. Put white mold oncultural practices, and field history. hold: Researchers identify resistant varieties. Soybean Digest. April. p. 34.References: Features a short list of 26 varieties with white mold resistance ratings observed over two1) Grau, Craig. 1998. White mold of soybean. seasons. University of WisconsinCooperative Extension. <http://plantpath.wisc.edu/ ~soyhome.pp/>. Larson, E. Anne and John VanDyk. 1999. Biological control against white mold. Iowa2) Gallepp, George. 1988. Keys to white mold State University, Ames, IA. July 12. control. Farmer’s Digest. August−September. <http://www.ipm.iastate.edu/ipm/icm/ p. 1−4. 1998/11-9-1998/biocontrolwm.html>.3) Grau, Craig, Edward S. Oplinger, and James E. Kurle. 1998. White mold in soybean: Lundeen, Peter and X.B. Yang. 1998. Soybean Soybean variety selection. University of white mold. Iowa State University, Ames, IA. Wisconsin Cooperative Extension, Madison, May 29. <http://www.exnet.iastate.edu/ WI. <http://plantpath.wisc.edu/ Pages/plantpath/whitemold/whtmld.html>. ~soyhome.pp/>.4) Agrios, George. 1988. Plant Pathology, 3rd North Central Soybean Research Program. edition. Academic Press, New York, NY. 2001. White Mold Coalition Website. <http:/ p. 430−431. /www.ncsrp.com/whitemold/>.5) Fravel, Deborah. 1999. Commercial North Dakota State Department of Plant biocontrol products for use against soilborne crop diseases. United States Department of Pathology. 1998. Proceedings of the Agriculture, Beltsville, MD. January 1. Sclerotinia Workshop: A Minnesota/North <http://www.barc.usda.gov/psi/bpdl/ Dakota In-Service Extension Workshop. bioprod.htm#Contans>. January 21. <http://www.ndsu.nodak.edu/ plantpath/sclero.htm>.6) Encore Technologies, LLC 111 Cheshire Lane, Ste. 500 Minnetonka, MN 55305 Uphoff, Michael, X.B. Yang, and John VanDyk. 612-404-9596 1999. Tolerance results to white mold and SDS. E-mail: email@example.com Iowa State University, Ames, IA. November 3. http://www.encoretechllc.com <http://www.ipm.iastate.edu/ipm/icm/ 1999/11-8-1999/wmsdstolres.html>.7) Westcott, Cynthia. 1971. Plant Disease Handbook, 3rd edition. Van Nostrand Reinhold Co., New York, NY. p. 351−353. Williams, Greg and Pat Williams. 2001. Worm castings for fungus control. HortIdeas. May.Additional Resources: p. 56.Diver, Steve. 1998. Compost Teas for Plant By George KuepperDisease Control. ATTRA Pest Management NCAT Agriculture SpecialistTechnical Note. While not discussed as an alternative December 2001 control option in the textthe author is unaware of any compost tea trials for white mold controlsuch materials might be The Electronic version of Organic Control of efficacious and could be worth White Mold on Soybeans is located at: investigating. Particularly relevant to this HTML is a discussion of “protective biofilms” http://www.attra.org/attra-pub/whitemold.html featured on the Soil Foodweb Inc. website at PDF http://www.attra.org/attra-pub/PDF/whitmold.pdf <http://www.soilfoodweb.com/leaf.html>.PAGE 4 //ORGANIC CONTROL OF WHITE MOLD ON SOYBEANS