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© 2009 Plant Management Network.
Accepted for publication 25 February 2009. Published 1 April 2009.


Effects of Diseases on Soybean Yields in the United States 1996 to 2007


Allen Wrather, University of Missouri-Delta Center, P.O. Box 160, Portageville, MO 63873; and Steve Koenning, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27695


Corresponding author: J. A. Wrather. wratherj@missouri.edu


Wrather, J. A., and Koenning, S. R. 2009. Effects of diseases on soybean yields in the United States 1996 to 2007. Online. Plant Health Progress doi:10.1094/PHP-2009-0401-01-RS.


Abstract

Research must focus on management of diseases that cause extensive losses, especially when funds for research are limited. Knowledge of yield suppression caused by various soybean diseases is essential when prioritizing research. The objective of this project was to compile estimates of soybean yield suppression due to diseases in the USA from 1996 to 2007. The goal was to provide information to help funding agencies and scientists prioritize research objectives and budgets. Yield suppression due to individual diseases varied among years. Soybean cyst nematode suppressed USA soybean yield more from 1996 to 2007 than any other disease. Phytophthora root and stem rot ranked second among diseases that most suppressed yield seven of 12 years. Seedling diseases and charcoal rot also suppressed soybean yield during these years. Research and extension efforts must be expanded to provide more preventive and therapeutic disease management strategies for producers to reduce disease suppression of soybean yield.


Introduction

Soybean yields in the USA have been suppressed by diseases in the past, and income derived from this crop has been less than optimal. This financial loss is important to rural economies and to the economies of allied industries in urban areas. Scientists and research funding agencies must focus their efforts and resources on management of diseases that most suppress yield, especially when funds for research are limited.

The Southern Soybean Disease Workers (SSDW) began estimating soybean yield suppression by diseases in the southern USA in 1974, and a summary of these results from 1974 to 1994 was published (6). Estimates of soybean yield suppression due to diseases for the USA from 1996 to 1998 (8), 1999 to 2002 (7), and 2003 to 2005 (9) were published through a joint effort of the North Central Regional Committee on soybean pathology (NCR-137) and the Southern Soybean Disease Workers. A common objective of these groups has been to monitor and publicize the development of new and recurring diseases of soybean in the USA.

The objective of this project was to compile estimates of soybean yields suppressed due to diseases for the USA during 1996 to 2007. The goal was to show the dynamics and magnitude of disease impacts on soybean yield and to aid funding agencies and scientists prioritize research objectives and budgets.


Methods for Developing Yield Suppression Estimates

Plant pathologists from each soybean-producing state in the USA were asked to estimate the percent each soybean disease suppressed yield in their state each year. These scientists listed their sources for developing estimates as field surveys, research plot data, diagnostic clinic records, and questionnaires to private crop consultants and university extension staff. Most individuals used several of these methods and consulted with their colleagues to develop estimates of percent each disease suppressed soybean yield during the year. Yield suppression values were based on estimates of yield in the absence of disease (8).


Estimates of Soybean Yield Suppression Due to Diseases

Estimates of soybean yield suppression due to diseases in each state are not shown. The total for soybean yields suppressed due to all diseases in the USA varied among years (Tables 1, 2, and 3); the total was lowest during 2007 and greatest during 1998.


Table 1. Estimated suppression of soybean yields (bushels) due to diseases for the United States from 1996 to 1999.x

Diseases 1996 1997 1998 1999
Anthracnose 3,878,000 9,004,000 6,942,000 3,040,000
Bacterial diseases 772,000 910,000 994,000 480,000
Brown spot 3,246,000 4,562,000 6,138,000 2,949,000
Brown stem rot 30,778,000 24,006,000 14,655,000 10,335,000
Charcoal rot 12,350,000 16,625,000 38,101,000 40,389,000
Downy mildew 341,000 262,000 884,000 122,000
Frogeye leaf spot 835,000 1,288,000 3,905,000 719,000
Fusarium root rot 1,232,000 2,423,000 3,184,000 3,516,000
Other diseases 1,673,000 9,741,000 941,000 1,954,500
Phomopsis seed rot 3,451,000 1,586,000 8,961,000 2,549,000
Phytophthora rot 40,486,000 53,626,000 42,227,000 26,141,000
Pod and stem blight 5,131,000 12,742,000 5,278,000 13,956,000
Purple stain 7,981,000 3,699,000 4,132,000 5,068,000
Rhizoctonia aerial blight 1,738,000 1,311,000 4,097,000 620,000
Root-knot & other nematodes 5,917,000 4,936,000 4,705,000 4,467,000
Rust 0 0 0 0
Sclerotinia stem rot 22,572,000 35,189,000 18,704,000 2,699,000
Seed diseases 4,510,000 290,000 1,682,000 491,000
Seedling diseases 31,345,000 24,508,000 28,550,000 12,317,000
Southern blight 206,000 246,000 339,000 260,000
Soybean cyst nematode 213,862,000 218,982,000 279,056,000 169,267,000
Stem canker 1,892,000 1,235,000 1,101,000 3,001,000
Sudden death syndrome 3,709,000 11,162,000 33,097,000 19,221,000
Virus 2,392,000 2,144,000 9,209,000 8,944,000
Total 400,297,000 440,477,000 516,882,000 332,505,500

 x Estimates are from 28 states.



Table 2. Estimated suppression of soybean yields (bushels) due to diseases for the United States from 2000 to 2003.x

Diseases 2000 2001 2002 2003
Anthracnose 1,497,000 7,333,000 6,325,000 10,973,000
Bacterial diseases 378,000 353,000 672,000 359,000
Brown spot 7,090,000 2,484,000 2,438,000 2,851,000
Brown stem rot 10,194,000 11,610,000 7,404,000 11,536,000
Charcoal rot 30,246,000 17,617,000 31,694,000 77,803,000
Downy mildew 697,000 103,000 79,000 313,000
Frogeye leaf spot 809,000 2,275,000 7,021,000 9,883,000
Fusarium root rot 1,590,000 9,522,000 15,568,000 5,935,000
Other diseases 3,722,000 2,688,000 2,245,000 2,240,000
Phomopsis seed rot 8,048,000 9,726,000 13,844,000 4,473,000
Phytophthora rot 39,545,000 51,086,000 45,953,000 55,544,000
Pod and stem blight 7,474,000 24,130,000 5,946,000 6,008,000
Purple stain 1,956,000 3,786,000 7,257,000 4,607,000
Rhizoctonia aerial blight 170,000 1,102,000 960,000 1,170,000
Root-knot & other nematodes 3,662,000 5,197,000 4,991,000 5,346,000
Rust 0 0 0 0
Sclerotinia stem rot 9,655,000 2,318,000 2,918,000 2,081,000
Seed diseases 406,000 353,000 337,000 515,000
Seedling diseases 21,946,000 31,090,000 21,840,000 28,307,000
Southern blight 330,000 159,000 180,000 250,000
Soybean cyst nematode 141,967,000 144,322,000 142,882,000 114,451,000
Stem canker 2,553,000 4,247,000 4,252,000 8,826,000
Sudden death syndrome 75,764,000 21,828,000 28,698,000 12,421,000
Virus 37,277,000 14,711,000 30,071,000 7,092,000
Total 398,656,000 368,039,000 383,575,000 372,982,000

 x Estimates are from 28 states.



Table 3. Estimated suppression of soybean yields (bushels) due to diseases for the United States from 2004 to 2007.x

Diseases 2004 2005 2006 2007
Anthracnose 16,083,000 16,427,000 18,113,000 10,008,000
Bacterial diseases 751,000 1,122,000 3,731,000 6,159,000
Brown spot 25,163,000 7,158,000 19,720,000 11,455,000
Brown stem rot 15,660,000 7,917,000 18,284,000 11,788,000
Charcoal rot 10,849,000 13,060,000 25,637,000 30,133,000
Downy mildew 535,000 564,000 5,418,000 1,337,000
Frogeye leaf spot 11,407,000 6,913,000 12,682,000 9,446,000
Fusarium root rot 9,457,000 5,512,000 6,215,000 5,804,000
Other diseases 8,983,000 529,000 2,045,000 150,000
Phomopsis seed rot 10,790,000 5,056,000 4,485,000 1,985,000
Phytophthora rot 57,116,000 41,977,000 53,808,000 25,086,000
Pod and stem blight 7,141,000 3,464,000 7,655,000 5,510,000
Purple stain 3,858,000 3,563,000 3,132,000 2,706,000
Rhizoctonia aerial blight 1,120,000 380,000 460,000 320,000
Root-knot & other nematodes 5,484,000 4,181,000 7,919,000 6,250,000
Rust 0 520,000 901,000 550,000
Sclerotinia stem rot 60,008,000 5,991,000 13,305,000 5,114,000
Seed diseases 174,000 2,588,000 680,000 1,080,000
Seedling diseases 44,082,000 32,638,000 39,885,000 33,905,000
Southern blight 290,000 210,000 190,000 180,000
Soybean cyst nematodey 136,722,000 76,210,000 123,778,000 93,981,000
Stem canker 14,994,000 6,557,000 7,779,000 5,055,000
Sudden death syndrome 42,329,000 19,849,000 27,320,000 22,078,000
Virus 2,243,000 1,601,000 7,451,000 6,767,000
Total 485,239,000 363,987,000 410,593,000 296,845,000

 x Estimates are from 28 states.

 y Estimates of yield suppression by SCN in 2005 do not include values from Iowa.


Soybean rust was first detected in the USA in late-fall 2004, but it did not have a measurable impact on soybean yields. Rust did suppress soybean yields in Georgia and South Carolina in 2005 (8), in Alabama, Georgia, Louisiana, and North Carolina in 2006 (2), and in Alabama, Arkansas, Georgia, Louisiana, Oklahoma, South Carolina, and Texas in 2007 (3).

Soybean cyst nematode (SCN) (Figs. 1 and 2) suppressed soybean yield in the USA more than any other disease from 1996 to 2007. The total for soybean yields suppressed due to SCN increased from 1996 to 1998 and then began a general decline to 2007. This may be due to greater awareness of SCN because of grower check-off funding for the Soybean Cyst Nematode Coalition, subsequent increased testing of field soils for the presence of SCN, and greater use of crop rotation and SCN resistant varieties.


 

Fig. 1. Soybean plants damaged by soybean cyst nematode.

 

Fig. 2. Soybean cyst nematode females developing on roots.


Phytophthora root and stem rot (PRSR) (Fig. 3) ranked second among diseases that most suppressed soybean yield seven of 12 years and ranked third on the list four of 12 years. Unlike the decline in yield suppression by SCN, the suppression of yield by PRSR has been about the same from 1996 to 2007.


 

Fig. 3. Soybean plants damaged and killed by Phytophthora root and stem rot.

 

Seedling diseases (i.e., Rhizoctonia, Pythium, Fusarium, and Phomopsis) ranked second to sixth among diseases that suppressed soybean yield from 1996 to 2007. The yield suppression due to this group of diseases was greater during the three years from 2005 to 2007 than any other three year period and was greater in years when cool, wet weather persisted after planting (7,8,9).

Charcoal rot (CR) (Fig. 4) suppressed soybean yields most often in Arkansas, Illinois, Indiana, Kansas, Kentucky, Missouri, Mississippi, and Tennessee. The total for soybean yield suppression due to CR was variable among years due to the impact of heat stress and drought on severity of this disease (7,8,9). Charcoal rot ranked second to sixth among diseases that suppressed soybean yield from 1996 to 2007.


 

Fig. 4. Soybean plants damaged and killed by charcoal rot.

 

Sclerotinia stem rot (SSR) (Fig. 5) suppressed soybean yields most often in Iowa, Illinois, Minnesota, Nebraska, Pennsylvania, South Dakota, and Wisconsin but seldom caused yield suppression in other states (7,8,9). The impact of SSR was greater during years when wet weather persisted during bloom (R1 and R2) of soybean. Yield suppression by SSR varied greatly among years; it was lowest during 2003 (2 million bushels) and greatest during 2004 (60 million bushels). It ranked among the top ten diseases that suppressed soybean yield in six of 12 years.


 

Fig. 5. Soybean plants damaged by Sclerotinia stem rot.

 

Frogeye leaf spot (FLS) (Fig. 6) was a problem for southern soybean producers from 1996 to 2007 but not in north central states from 1996 to 2000. It did begin to suppress yields in some north central states during 2001, and yield suppression by FLS increased in this area from 2003 to 2007. FLS ranked among the top ten diseases that suppressed yield from 2003 to 2007.


 

Fig. 6. Frogeye leaf spot lesions on soybean leaves.

 

Sudden death syndrome (SDS) (Fig. 7) ranked among the top ten diseases that suppressed soybean yield in the USA in 11 of 12 years and often ranked second to fifth. Yield suppression was lowest in 1996 and greatest in 2000. SDS suppressed soybean yields often in Iowa, Illinois, and Indiana, and it did suppress yields in Arkansas, Missouri, Tennessee, Kentucky, Minnesota, and Wisconsin in some years (7,8,9). Scherm and Yang (5) determined that weather patterns were more conducive for this disease in the central USA than other areas, and our data confirm their observation.


 

Fig. 7. Soybean leaves damaged by sudden death syndrome.

 

Li and Yang (4) were able to group the fungal diseases that most suppressed yield in the USA from 1996 to 2005 based on optimal temperature for disease development, host ranges, characteristics of disease cycle, the pathogenís survival capacity, and other characteristics.

Diseases greatly suppressed soybean yields in the USA from 1996 to 2007. The impact of diseases on USA soybean production may have been more severe if not for grower adoption of disease management strategies. Research and extension efforts must be expanded to provide more effective preventive and therapeutic disease management strategies that will further reduce disease suppression of yield.

Reliable estimates of crop losses to diseases based on precise methodology and crop loss models have been useful for defining the severity of various diseases (1). It is hoped that estimates of soybean yield suppression due to diseases based on precise methodology will be available in the future.


Acknowledgments

This work was supported, in part, by the Missouri and North Carolina Agriculture Experiment Stations. This work was also supported by the USA soybean farmer checkoff through the United Soybean Board. The authors thank Joyce Elrod for her efforts in this project and thank God for guidance.


Literature Cited

1. James, W. C., Teng, P. S., Nutter, F. W. 1991. Estimated losses of crops from plant pathogens. Pages 15-51 in: CRC Handbook of Pest Management, CRC Press, Boca Raton, FL.

2. Koenning, S. R. 2007. Southern United States soybean disease loss estimates for 2006. P. S. Soybean Dis. Work. 34:1-6.

3. Koenning, S. R. 2008. Southern United States soybean disease loss estimates for 2007. P. S. Soybean Dis. Work. 35:1-6.

4. Li, X., and Yang, X. B. 2009. Similarity, pattern, and grouping of soybean fungal diseases in the United States: Implications for the risk of soybean rust. Plant Dis. 93:162-169.

5. Scherm, H., and Yang, X. B. 1999. Risk assessment of sudden death syndrome of soybean in the north-central United States. Agric. Sys. 59:301-310.

6. Wrather, J. A., Chambers, A. Y., Fox, J. A., Moore, W. F., and Sciumbato, G. L. 1995. Soybean disease loss estimates for the southern United States, 1974 to 1994. Plant Dis. 79:1076-1079.

7. Wrather, J. A., Koenning, S. R., and Anderson, T. R. 2003. Effect of diseases on soybean yields in the United States and Ontario (1999-2002). Online. Plant Health Progress doi:10.1094/PHP-2003-0325-01-RV.

8. Wrather, J. A., Stienstra, W. C., and Koenning, S. R. 2001. Soybean disease loss estimates for the United States from 1996 to 1998. Can. J. Plant Pathol. 23:122-131.

9. Wrather, J. A., and Koenning, S. R. 2006. Estimates of disease effects on soybean yields in the United States 2003 to 2005. J. Nematol. 38:173-180.