kudzu and soybean rust - amazon s3...intro-duced into the united states from asia in the 19th...

KUDZU AND SOYBEAN RUST

DOI: 10.1564/v25_apr_06 O u t l o o k s o n Pe s t M a n age m e n t – A p r i l 2 0 1 4 1 7 5

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KUDZU: INVASIVE WEED SUPPORTS THE SOYBEAN RUST PATHOGEN THROUGH WINTER MONTHS IN SOUTHEASTERN UNITED STATES

Edward J. Sikora, Alabama Cooperative Extension System and the Department of Entomology and Plant Pathology, Auburn University, Alabama, USA

Keywords: kudzu, Pueraria montana var. lobata, soybean rust, SBR, Phakopsora pachyrhizi, soybean

The “Vine that ate the South”Kudzu (Pueraria montana var. lobata) is a large trifoliate-leaved, semi-woody, trailing or climbing perennial vine that belongs to the legume family (Everest et al., 1999). Intro-duced into the United States from Asia in the 19th century it has since become a serious invasive plant and a recogniz-able symbol of the American Southeast (Everest et al., 1999; Miller & Edwards, 1983). Kudzu often becomes a weed in non-cropland areas such as roadsides, unused fields, vacant lots or abandoned buildings often dominating the landscape (Figure 1). Kudzu vines can climb to 30 m and spread 15–18 m in a single growing season (Miller & Edwards, 1983). The ability of kudzu to grow quickly, survive in areas of low nitro-gen availability, and acquire resources efficiently due to an extensive root system allows the plant to out-compete native species (Forseth & Innis, 2004). As a result of its rapid growth rate the plant has the ability to climb over trees and shrubs, eventually killing them with its dense canopy through which little light can penetrate (Figure 2).

Kudzu was first introduced to the U.S. in 1876 and became widely marketed as an ornamental plant to shade courtyards and porches of southern homes (Miller & Edwards, 1983). In the early 1900s, kudzu was promoted as an inexpensive forage crop for livestock, but reached its greatest level of prominence

Figure 1. Kudzu often becomes a weed in non-cropland areas such as in roadsides and unused fields often taking over the landscape. (Photo courtesy of Edward Sikora).

Edward Sikora

Figure 2. Kudzu has the ability to climb over trees and shrubs, eventually out-competing other plants in the landscape for sunlight with its dense canopy. (Photo courtesy of Edward Sikora).

in the 1930s when it was widely planted in the South for soil erosion control (Britton et al., 2002). The federal government offered landowners up to $20.00 per ha as an incentive to plant their land to kudzu, and more than 1.2 million ha were planted on farms by 1946 (Everest et al., 1999).

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By the 1950s kudzu began to lose its attractiveness as its vines spread across the southern landscape unchecked. In 1953, the United State Department of Agriculture (USDA) removed kudzu from the list of acceptable cover crops and in 1970 the agency lowered the plant’s status to common weed (Miller & Edwards, 1983). In 1998, kudzu was listed by the U.S. Congress as a Federal Noxious Weed (Blaustein, 2001). This did not hinder kudzu as its range continued to expand and is now estimated to cover over 3 million ha of the Eastern U.S. and is present in 31 of the 50 states (USDA National Resources Conservation Service). Severe infestations of kudzu occur in Alabama, Georgia and Mississippi with more than 100,000 ha of land estimated to be infested in Alabama (Ever-est et al., 1999).

Economic damage from kudzu includes lost income from forestry, control costs for utilities and agriculture, and management efforts in national and state parks (Forseth & Innis, 2004). The economic impact of kudzu in the U.S. is esti-mated at $100–500 million lost per year in forest productiv-ity (Blaustein, 2001). Costs from power companies to control kudzu have been estimated at $1.5 million a year (Britton et al., 2002). Control requires persistent management practices that may include repeated mowing or cutting-back, graz-ing by livestock, prescribed burning and/or repeated use of herbicides (Everest et al., 1999). Even when done correctly an established population of kudzu may require up to 10 years to eradicate with herbicides.

Soybean rust invades the United StatesKudzu has done its share of damage as an invasive weed but also took on increased importance in the U.S. as the most common overwintering host for the fungus Phakopsora pach-yrhizi, the causal organism of soybean rust (SBR). SBR is a foliar disease of soybean that has caused significant crop losses in all parts of the world where it is established (Bromfield 1984; Hartman et al., 1991; Pivonia et al., 2005; Yorinori et al., 2005). The disease cost growers in Brazil $500 million in yield losses and $700 million in fungicide costs in 2002 (Yori-nori et al., 2002). SBR damages plants by attacking the foliage causing leaf lesions and loss of photosynthetic area resulting in premature defoliation of infected plants (Figure 3). Prema-turely defoliated soybeans produce fewer pods, fewer seeds per pod, and poorly filled seed which results in reduced yields.

The U.S. is the largest producer of soybeans in the world, averaging a production of 69,682 thousand metric tons of beans (USDA National Agricultural Statistics Service). Since 2004, soybeans have been produced on approximately 30 million ha annually in the U.S., with a value between $18 and $32 billion. Though the majority of soybeans are grown in the Midwest, production extends into the southeast and along the eastern seaboard. Typically, the southernmost states begin planting first during the season and then the most north-ern areas plant as more moderate temperatures prevail. The soybean growing season can extend from late March through late November in parts of the southern region.

SBR was first identified in the continental U.S. in Novem-ber 2004 (Schneider et al., 2005). Early predictions based on high levels of overwintering inoculum suggested that without effective management, losses in soybean could exceed 80%

(Caldwell & McLaren, 2004; Hartman et al., 1991). While these loss estimates have not yet been approached in the U.S., yield losses from the disease have occurred sporadically in southern states. SBR was especially problematic in Alabama in 2012 when the disease reduced yield by up to 60% in over 200 ha of poorly managed soybeans (Sikora et al., 2013). These are the greatest yield losses documented in the U.S. as a result of SBR, and are equivalent to losses observed in South America in the early 2000s (Morel & Yorinori, 2002; Yori-nori et al., 2005).

The anticipated threat of SBR resulted in an unprece-dented effort to develop and implement disease monitoring and education platforms in North America. Since 2005, the primary platform for SBR information dispersal, known as the Soybean Rust-Pest Information Platform for Extension and Education (SBR-PIPE) has relied on real-time disease monitoring observations to track and predict in-season spread of SBR in North America (Giesler & Hershman, 2005). Real-time observations can be viewed on the publically avail-able website located at: http://SBR.ipmpipe.org/cgi-bin/SBR/public.cgi.

Invasive weed aids soybean rust survivalObservations gained from disease monitoring have greatly improved our understanding of SBR. Monitoring efforts have helped identify and quantify the role of additional hosts in rust development and the pathogen’s ability to survive soybean-free periods during the winter in the U.S. Kudzu is now considered the primary overwintering host in the U.S. and important to potential SBR epidemics in this country (Sun et al., 2005). SBR-infected kudzu leaves that survive the winter, and new kudzu leaves that are infected prior to soybean emergence in the spring, serve as a bridge for SBR inoculum increase and northward spread into the soybean producing areas of the U.S.

Initially it was believed that P. pachyrhizi could only survive the winter primarily on kudzu in parts of Florida and southern Texas, and occasionally in coastal areas in states bordering the Gulf of Mexico. This was suggested because all known hosts of P. pachyrhizi in the U.S. could not survive

Figure 3. Defoliation due to soybean rust contributes to yield loss. (Photo courtesy of Edward Sikora).


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extended periods of freezing temperatures (Pivonia & Yang, 2004). Predictions on the overwintering dynamics of SBR in the U.S. were supported by a University of Florida study that reported that P. pachyrhizi survives in patches of kudzu year-round in the central portion of that state and has the potential to produce viable urediniospores, the reproductive structure of the fungus that infects susceptible hosts, in the field well into winter, even in the panhandle of Florida (Jurick II et al., 2008). Researchers also observed that temperatures below 0°C and prolonged drought can result in defoliation of kudzu which limits inoculum production in host tissue and reduces the chance for P. pachyrhizi survival in a given loca-tion. However, even though kudzu is a susceptible plant and can increase the potential spread of the fungus, some kudzu patches are naturally resistant or immune to infection from the fungus (Bonde et al., 2009; Jordan et al., 2010).

The Alabama SBR monitoring program was initiated in December, 2004, shortly after the disease was first detected in the state (Mullen et al., 2006; Sikora et al., 2009). The program included monitoring soybeans for SBR develop-ment during the growing season as well as searching for SBR-infected kudzu overwintering sites. Monitoring efforts for overwintering sites initially focused on large kudzu patches in rural areas along roadsides and in unused fields where kudzu’s growth often goes unchecked during the summer. Kudzu typi-cally dies back to the ground when temperatures drop below freezing and this appeared to be the case across Alabama even in areas along the Gulf Coast (Sikora & Delaney, 2006). Based on these early observations combined with the historic winter-weather patterns in the southeast it appeared that the only source of SBR inoculum in the U.S. at this time would be found in south Florida.

Urban Heat Islands and winter survival of Kudzu Alternative evidence began to emerge in January, 2006 when green kudzu leaves were observed along the surface of a bridge abutment below an overpass along a major highway in the central Alabama city of Montgomery (Figure 4). On

closer examination, it was observed that most of the kudzu had died-back but the remaining green foliage showed symp-toms of SBR which was later confirmed to be P. pachyrhizi (Sikora et al., 2007). Over the next six weeks four more rela-tively small patches of SBR-infected kudzu were detected in this urban environment. These sites were typically associated with buildings, concrete and/or asphalt; materials which effec-tively retain heat (Figure 5). The buildings could also block wind, inhibiting cooling (Oke, 1987). These areas are termed “urban heat islands” (UHI) and experience elevated tempera-tures compared to outlying rural surroundings (Oke, 1997). The annual mean air temperature of a city with one million or more people can be 1 to 3°C warmer than its surroundings, and on a clear, calm night, this temperature difference can be as much as 12°C (Akbari, 2005). These UHIs provided condi-tions that were favorable for year-round kudzu survival and in turn an overwintering host for P. pachyrhizi much farther north than originally anticipated. The Montgomery sites are located over 200 km north of the panhandle of Florida; the farthest north the pathogen had been found to overwinter in the U.S. (Sikora et al., 2007).

The discovery of overwintering kudzu harboring SBR in Montgomery shifted subsequent scouting efforts towards potential overwintering sites in urban areas rather than rural settings. By the end of February, 2006, SBR was detected in five additional sites in south Alabama. These sites were all in urban areas and associated with UHI structures (i.e. aban-doned buildings) where protection from freezing tempera-tures was provided (Figure 6).

Monitoring efforts in successive years for SBR-infected kudzu in urban locations have provided some measure of inoculum potential for the impending soybean production season. In April, 2013, P. pachyrhizi was detected on kudzu that survived the winter under the Edmond Pettus Bridge that spans the Alabama River in Selma, Alabama (Sikora, 2013). The bridge, which is a National Historic Landmark for its role in the civil rights movement in the U.S., is now the north-ern most point where P. pachyrhizi has successfully survived the winter in the U.S. (Figure 7).

SBR has successfully overwintered on kudzu in Alabama every year between 2006 and 2013 except for 2011 and in

Figure 4. Green, soybean rust-infected kudzu leaves below a highway overpass in Montgomery, Alabama. (Photo courtesy of Edward Sikora).

Figure 5. Soybean rust infected kudzu surviving the winter near foundation of an abandoned building in Montgomery, Alabama. (Photo courtesy of Edward Sikora).

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each case was observed in an urban area. In four of these years, P. pachyrhizi was detected past April 30th which is beyond the average last-frost dates (March 21–31st) for these locations (http://www.plantmaps.com/interactive-alabama-last-frost-date-map.php). In 2006 and 2012, SBR-infected kudzu survived as far north as Montgomery; and in 2013 was found in both Montgomery and Selma, Alabama. In addition to these central Alabama locations, P. pachyrhizi has also been detected on kudzu in urban areas near the Gulf Coast in Alabama, Florida, and Louisiana in most years since 2005 (http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi).

Climate change, global warming and soybean rustThe significance of these isolated kudzu sites in central Alabama in relation to the overall SBR inoculum levels prior to the soybean growing season is not well understood. Kudzu and other hosts of P. pachyrhizi found in south Florida, Mexico and the Caribbean Basin are generally considered more important sources of inoculum when considering a potential SBR epidemic in the U.S. However, with the poten-tial of climate change providing milder temperatures during the winter months (Hatfield et al., 2011), these urban islands of SBR-infected kudzu could become much more significant sources of inoculum that would increase the threat to the U.S. soybean industry.

Predictions of global warming include increases of 3 to 5°C in mean global temperatures (IPCC 2001). Trends over the last few decades in the U.S. include a decrease in the number of frost days, and earlier date for the last frost in spring, and a later date for the last frost in fall (Easterling, 2002). All of these trends should favor the spread of kudzu northward and potentially increase the levels of SBR inoculum that overwin-ters successfully in the south.

Even in the absence of climate change the importance of the connection of kudzu survival in UHIs is an important new consideration in forecasting risk of early-season SBR outbreaks in commercial soybeans.

References Akbari, H. 2005. Energy saving potentials and air quality benefits

of urban heat island mitigation. LBNL-58285. Berkeley, CA: Lawrence Berkeley National Laboratory, USA.

Blaustein, R. J. 2001. Kudzu’s invasion into Southern United States life and culture. In The Great Reshuffling: Human Dimensions of Invasive Species. pp 55–62 (Ed J. A. McNeeley). IUCN, The World Conservation Union, Gland, Switzerland and Cambridge, UK.

Bonde, M. R., Nester, S. E., Moore, W. F. & Allen, T. W. 2009. Comparative susceptibility of kudzu accessions from the southeastern United States to infection by Phakopsora pachyrhizi. Plant Disease 93, 593–598.

Britton, K. O., Orr, D. & Sun, J. 2002. Kudzu. In Biological control of invasive plants in the Eastern United States. pp325–330 (Eds R. Van Driesche, S. Lyon, B. Blossey, M., Hoddle & R. Reardon). USDA Forest Service Publication FHTET-2002-04. USDA Forest Service, Morgantown, West Virginia, USA.

Bromfield, K. R. 1984. Soybean rust, Monograph (American Phytopathological Society), No. 11. American Phytopathological Society. St. Paul, MN, USA.

Caldwell, P. & McLaren, N. W. 2004. Soybean rust research in South Africa. In Proc. VII World Soybean Res. Conf., IV Int. Soybean

Figure 6. Soybean rust infected kudzu surviving the winter in association with an abandoned building in Mobile, Alabama. (Photo courtesy of Edward Sikora).

Figure 7. Soybean rust-infected kudzu successfully overwintering in Selma, Alabama in 2013; the northern most point where P. pachyrhizi has survived the winter in the U.S. (Photo courtesy of Edward Sikora).


O u t l o o k s o n Pe s t M a n age m e n t – A p r i l 2 0 1 4 1 7 9


Processing and Utilization Conf. pp354–360. (Eds F. Moscardi, C. B. Hoffman-Campo, O. Ferreira Saraiva, P. R. Galerani, F. C. Krzyzanowski & M. C. Carrão-Panizzi). III Congresso Mundial de Soja. Embrapa Soybean, Londrina, Brazil.

Easterling, D. R. 2002. Recent changes in frost days and the frost-free season in the United States. Bulletin of the American Meteorological Society 83, 1327–1332.

Everest, J. W., Miller, J. H., Ball, D. M. & Patterson, M. 1999. Kudzu in Alabama history, uses, and control. Alabama Cooperative Extension System ANR-65, AL, USA.

Forseth, Jr., I. N. & Innis, A. F. 2004. Kudzu (Pueraria montana): History, physiology, and ecology combine to make a major ecosystem threat. Critical Reviews in Plant Sciences 23, 401–413.

Giesler, L. J. & D. E Hershman. 2005. Overview and value of sentinel plots for 2005. In Proceedings of the 2nd National Soybean Rust Symposium, American Phytopathology Society, Nashville, TN, USA.

Hartman, G. L., Wang, T. C. & Tschanz, A. T. 1991. Soybean rust development and the quantitative relationship between rust severity and soybean yield. Plant Disease 75, 596–600.

Hatfield, J. L., Boote, K. J., Kimball, B. A., Ziska, L. H., Izaurralde, C., Ort, D. & Thomson, A. 2011. Climate impacts on agriculture: Implications for crop production. Agronomy Journal 103, 351–370.

Intergovernmental Panel on Climate Change. 2001. The scientific basis. Contribution of working group I. In Climate Change 2001: Third Assessment Report of the Intergovernmental Panel on Climate Change. (Eds J. T. Houghton, Y. Ding, D. J. Griggs, M. Noguer, P. J. van der Linden, X. Dai, K. Maskell & C. A. Johnson) Cambridge: Cambridge University Press, UK.

Jordan, S. A., Mailhot, D. J., Gevens, A. J., Marois, J. J., Wright, D. L., Harmon, C. L. & Harmon, P. F. 2010. Characterization of kudzu (Pueraria spp.) resistance to Phakopsora pachyrhizi, the causal agent of soybean rust. Phytopathology 100, 941–948.

Jurick II, W. M., Narvaez, D. F., Brennan, M. N., Harmon, C. L., Mariois, J. J., Wright, D. L. & Harmon, P. F. 2008. Winter survival of the soybean rust pathogen, Phakopsora pachyrhizi, in Florida. Plant Disease 92, 1551–1558.

Miller, J. H. & Edwards, B. 1983. Kudzu: Where did it come from? And how can we stop it? Southern Journal of Applied Forestry 7, 165–169.

Morel, W. & Yorinori, J. T. 2002. Situacion de la roja de la soja en el Paraguay. Bol de Diulgacion No. 44. Ministerio de Agricultura y Granaderia, Centro Regional de Investigacion Agricola, Capitan Miranda, Paraguay.

Mullen, J. M., Sikora, E. J., McKemy, J. M., Palm, M. E., Levy, L. & Devries-Paterson, R. 2006. First report of Asian soybean rust caused by Phakopsora pachyrhizi on soybeans in Alabama. Plant Disease 90, 112.

Oke, T. 1987. Boundary Layer Climates, 2nd ed., Methuen, London, UK.

Oke, T.R. 1997. Urban Climates and Global Environmental Change. In Applied Climatology: Principles & Practices. 273–287. (Eds R. D. Thompson & A. Perry, A.) New York, NY, USA: Routledge.

Pivonia, S. & Yang, X. B. 2004. Assessment of the potential year-round establishment of soybean rust throughout the world. Plant Disease 88, 523–529.

Pivonia, S., Yang, X. B. & Pan, Z. 2005. Assessment of epidemic potential of soybean rust in the United States. Plant Disease 89, 678–682.

Schneider, R. W., Hollier, C. A., Whitam, H. K., Palm, M. E., McKemy, J. M., Hernandez, J. R., Levy, L. & DeVries-Paterson, R. 2005. First report of soybean rust caused by Phakopsora pachyrhizi in the continental United States. Plant Disease 89, 774.

Sikora, E. J. & M. Delaney. 2006. Kudzu in the city: detection of Asian soybean rust on kudzu in urban environments in Alabama during the winter of 2006. (abs). Soybean Rust Symposium, St. Louis, MO, USA.

Sikora, E. J., Delaney, D., Delaney, M. & Mullen, J. 2007. Asian soybean rust in Alabama. Alabama Cooperative Extension System ANR-1310, AL, USA.

Sikora, E. J., Delaney, D. & M. Delaney. 2009. Developing an innovative team approach to address a newly introduced disease of soybeans in the United States. Journal of Extension: http://www.joe.org/joe/2009august/iw7.php (Accessed 4-01-2014)

Sikora, E. J. 2013. Observations on soybean rust management in Alabama in 2012. In Proceedings of the Southern Soybean Disease Workers. 40th Annual Meeting, March 13–14 2013, Pensacola Beach, FL, USA.

Sun, J. H., Li, Z. C., Jewett, D. K., Britton, K. O., Ye, W. H. & Ge, X. J. 2005. Genetic diversity of Pueraria lobata (kudzu) and closely related taxa as revealed by inter-simple sequence repeat analysis. Weed Res. 45, 255–60.

Yorinori, J. T., Pavia, W. M., Frederick, R. D. & Fernandez, P. F. T. 2002. Ferrugem da soja (Phakopsora phayrhiza) no Brasil e no Paraguai, nas safras 2000/01 e 2001/02. In Congresso Brasileiro de Soja (Foz do Iguacu, PR). Embrapa Soja, Londrina, Paraguay.

Yorinori, J. T., Paiva, W. M., Frederick, R. D., Costamilan, L. M., Bertagnolli, B. F., Hartman, G. E., Godoy, C. V. & Nunez, Jr., J. 2005. Epidemics of soybean rust (Phakopsora pachyrhizi) in Brasil and Paraguay from 2001 to 2003. Plant Disease 89, 675–677.

Edward Sikora is a Professor and Extension Plant Pathologists for the Alabama Cooperative Extension System and Auburn University. He received his B.S. degree in Zoology from Eastern Illinois University, and later earned M.S. and Ph. D. degrees in Plant Pathology from the University of Illinois. His exten-sion/research program focuses on developing and implementing integrated pest management practices for commercial production systems for soybean, vegetable, tree fruit and small fruit crops. Sikora has managed the soybean rust monitoring program for Alabama since 2004, and became the coordinator of the National sentinel plot monitoring program for soybean rust in 2010.

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kudzu and soybean rust - amazon s3...intro-duced into the united states from asia in the 19th...

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