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Leonor Leandro

Dr.  Leonor Leandro photo
Collaborator
Associate Professor
Area of Expertise: 
Plant Pathology

Cropping System Diversification Reduces Severity and Incidence of Soybean Sudden Death Syndrome

A research study published in the American Phytopathological Society (APS) Plant Disease journal examined the effects of cropping system diversification on management of soybean sudden death syndrome (SDS), caused by Fusarium virguliforme, that provides some insight into preventing the disease for growers. SDS is a major disease that impacts North and South America. Estimates of annual yield losses in the United States due to SDS have ranged between 0.6 and 1.9 million metric tons during the years from 2006 to 2014, accounting for $200 to 750 million in monetary losses over the same time.

The study included a 2-year, 3-year, and 4-year crop rotation as well as a control. The rotations were as follows:

·      2-year: corn-soybean

·      3-year: corn-soybean-oat (with a red clover cover crop)

·      4-year: corn-soybean-oat-alfalfa

The study also examined differing crop practices, with manure application on the 3 and 4-year rotations and reduced rates of fertilizers, as well as weed management regimens. The study took place between 2010 and 2015.

Analysis shows cropping system diversification can be an effective strategy to manage SDS, especially when incorporating oat, clover and/or alfalfa into an annual crop rotation. Even in years when SDS disease pressure was low, the strategies’ effect was consistent over six years. SDS severity was 17 times higher in two-year cropping system plots, compared with extended and diversified systems, specifically four-year systems. F. virguliforme was isolated at higher frequency from roots from the 2-year system compared with the more diversified systems in 2012 and 2013.

Low levels of SDS in 2011 and 2012 may be explained by the amount of precipitation in those years. Development of SDS is highly dependent on soil moisture, and higher-than-average precipitation, especially during soybean reproductive stages, has been associated with SDS epidemic years. All 4 years of the study when severe SDS symptoms were observed had one or more months during the growing season where rainfall greatly exceeded the monthly average.

When it came to yield results, three and four-year systems showed 40 percent greater yields than in two-year systems. Between 50-87 percent of yield variance was explained by SDS incidence; SDS severity caused 30-70 percent variation in yields.

Extended and diversified cropping systems were correlated with lower F. virguliforme population densities. In both soybean and corn plots sampled in 2012 and 2013, the pathogen’s density in the soil was approximately fivefold greater in the two-year system, as compared to the four-year system. F. virguliforme can survive in soil for years as thick-walled chlamydospores and rotation with corn has been shown to be ineffective for reducing F. virguliforme soil populations or SDS symptoms.

The explanation for higher SDS severity and pathogen presence in the two-year system may be the result of the greater frequency of soybean planting, which creates inoculum build-up in the soil. Corn residue can support survival of the SDS pathogen, which could help explain increased SDS in two year rotations. It is possible alternating corn and soybean is more conducive to SDS than is interruption of that cycle with other crops.

Alfalfa and clover are susceptible to F. virguliforme infection, thus pathogen reduction in the extended rotation may be more closely attributed to the inclusion of oats. In addition, oat used in rotation or as a cover crop has been shown to suppress root rot diseases on certain crops because it produces avenacins, which are active saponin compounds that have antimicrobial activity against several fungal pathogens.

Diversified cropping systems, especially those integrated with livestock production, offer numerous potential environmental and agronomic benefits, including improved soil quality, greater nutrient cycling and retention, greater water-holding capacity, lower rates of soil erosion, and improved control of weeds, diseases, and insect pests. The loss of crop diversity in the Midwestern United States, due especially to reductions in small grain, hay, and pasture production, is linked with significant reductions in livestock production in the region, thus the reduction of manure application to fields. The study asserts that adoption of diversified systems will require growers to learn new practices and adapt to new farming equipment, which could serve to benefit growers financially in the long-run, by limiting yield loss.

Project Type: 
Duration: 
11/05/2018
Category: 

Effect of Tillage and Cultivar on Plant Population, Sudden Death Syndrome, and Yield of Soybean in Iowa

Sudden death syndrome (SDS) affects soybeans around the world and accounts for millions of tons of yield loss in the United States and Canada, ranking it as one of the top 10 yield-reducing diseases of soybean for 16 years. Managing SDS has been difficult with the lack of effective foliar fungicides and completely resistant cultivars, environmental influences and inconsistent management practices.

The researchers in the study aimed to determine the impact conservation tillage had in relation to SDS. Conservation tillage practices have become common practice to preserve soil moisture and prevent erosion, and has shown results in reducing soybean cyst nematode (SCN) populations in the field. Both SCN and SDS have a linked severity, but SDS also has a positive correlation with the soil moisture content.

The field experiments took place in Iowa in a field with a history of SDS and were evaluated for five consecutive years. Data showed there were differences in root rot severity and foliar disease symptoms across the years among different cultivars, but this was not due to tillage. Although yields were different across the years, researchers write that this was not due to tillage and can be explained by seeding rates and sufficient rainfall. The study confirms using resistant cultivars is the best practice to fight SDS, and that seed treatment, SCN management and diversification in cropping systems can aid in disease resistance. In all, incidences of SDS were not dependent on tillage method, as the incidence of disease was consistent throughout the study. SDS resistant cultivars would make the most impact.  

This study was published in 2019. To view the whole study, click here.

Project Type: 
Duration: 
03/04/2019
Category: 

Research proves herbicide selection non-issue with SDS

May 15, 2014

Sudden death syndrome in soybeanThe world’s most widely used weed killer is not responsible for perpetuating Sudden Death Syndrome (SDS) in soybeans, research shows. A collaborative effort among soybean researchers in the United States and Canada and found that glyphosate does not increase SDS severity or adversely affect yields in soybean fields. Scientists from five Midwest universities and the Ontario Ministry of Agriculture Food and Rural Affairs, led by Daren Mueller of Iowa State University (ISU) in Ames, participated in the three-year study.

Risk of Sudden Death Syndrome Increasing with Rains

July 7, 2014

One thing we have learned from outbreaks of sudden death syndrome (SDS) in years past is that this disease likes it wet. Last year we wrote about the risk of SDS  increasing with the early season rain. But at the end of the article we threw in one caveat – soybeans were planted very late in the season, which reduced the risk of SDS developing. And after we published the article, the rains essentially stopped. Fast forward to the end of the 2013 season -- we still had some SDS in parts of Iowa in 2013, but it was not as nearly as bad as it could have been.

Be on the Lookout for Brown Stem Rot in Soybean

August 12, 2014

Soybean diseases are starting to show up in Iowa fields this growing season. In an On-Farm Network trial in north central Iowa, brown stem rot (BSR) was recently found. This disease is caused by the fungus Phialophora gregata, and infection can result in yield loss for Iowa farmers.

Quantifying soybean yield losses due to sudden death syndrome (SDS)

Muhammad Mohsin Raza, a graduate research assistant at Iowa State University in the Plant Pathology and Microbiology department, discusses his research project in this video. Sudden death syndrome is one of the major yield-limiting diseases of soybean and has widely spread across soybean producing states in the U.S. Every year; farmers suffer substantial yield losses due to this disease. Because of the limited understanding of the impact of SDS on soybean yield, it makes it difficult for farmers to decide whether or not to apply management tactics.

Detecting soybean sudden death syndrome using remote sensing

Muhammad Mohsin Raza, a graduate research assistant at Iowa State University in the Plant Pathology and Microbiology department, discusses his research project in this video. Soybean sudden death syndrome is a disease of major economic importance in the North and South Americas regarding yield losses. Monitoring soybean health and detecting SDS at initial crop stages is essential to facilitate sustainable, environment-friendly, and cost-effective management practices in grower’s fields.