.

October 5, 2007
Source: Farms.com, University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources report [edited] <http://www.farms.com/news/readstory.asp?storyid=12612>

Soybean rust was positively identified for the 1st time this week in Nebraska. It was detected in a south eastern Nebraska soybean field. Identification was confirmed at UNL's [University of Nebraska-Lincoln] Plant and Pest Diagnostic Clinic and the National Plant Diagnostic Network regional lab at Kansas State University Friday (5 Oct 2007). The disease was found on soybeans in south eastern Richardson County near the town of Rulo and in Otoe County south of Nebraska City. Leaf samples were collected from scouting activity by Seth Watson, UNL soybean rust sentinel plot coordinator, on 3 Oct 3 2007.

Samples of hundreds of leaves were collected as part of scouting activity with the national soybean rust sentinel plot system. The sentinel plot system is funded by the Soybean Checkoff program and the US Department of
Agriculture. "As we are late in the season and many of our identified sentinel plots are mature at this time, leaf samples were being collected from fields with green leaves remaining starting on Monday [8 Oct 2007] of this week," said Loren Giesler, UNL Extension plant pathologist. "Based on where other reports of soybean rust had been confirmed in southern Kansas and near Des Moines, Iowa, we thought it should be here."

Giesler said the find is not unexpected as the disease has been found in many states this year [2007] and has been moving north from its overwintering location in the Gulf States and spread into Texas earlier this summer. Institute of Agriculture and Natural Resources faculty and staff are working to determine if other fields in the state also have rust. "Fortunately for soybean producers this year, the disease is showing up too late for any impact on yield, and management will not be needed," Giesler said.

Further finds on the distribution and severity of rust occurrence this year [2007] will greatly help forecasting and modeling research, which is ongoing. "This demonstrates the ability of the fungus to move northward, and had it occurred earlier in the year a totally different scenario could have developed," he said. Updates on where soybean rust has been confirmed in Nebraska and other parts of the US can be found on the USDA [US Department of Agriculture] soybean rust website at <http://sbrusa.net>.

"As mentioned, no management will be needed this year [2007] for soybean rust in Nebraska, but growers should continue to stay aware of where soybean rust is being found in future years," Giesler said. "Each year the disease has spread north and west earlier, and this year we have observed a totally different distribution compared to last year [2006]. No rust was observed in the western soybean states in the Great Plains area last year compared to this year, and this year we are seeing movement north further west than last year's movement up the Mississippi Delta into Ohio."

If rust arrives earlier in the season in future years, management options will include fungicide application, but once the crop reaches the R6 growth stage (full berry stage), the impact of soybean rust is minimal and most fungicides cannot be applied based on the minimum pre-harvest intervals.

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[2]
Date: Wed 3 Oct 2007
Source: Reuters [edited]
<http://www.reuters.com/article/reutersEdge/idUSN0323663420071003>

Arrival of the soybean rust fungus into the top soybean-producing states of Iowa and Illinois will not hurt yields in 2007, but US plant pathologists and the industry urged growers on Wednesday [3 Oct 2007] not to become complacent.

Soybean rust, which can slash yields by up to 80 per cent on untreated fields, was found last week [24-30 Sep 2007] in central Iowa, southern Illinois, and parts of Missouri. State officials said those cased posed no risk to this year's [2007] harvest. This year the fungus has been found in 157 counties in 14 states, up from 88 counties in 8 states at this time last year [2006]. The greatest concentration has been in eastern Oklahoma, eastern Texas, Arkansas, Louisiana, south western Alabama, and the Florida panhandle.

"The disease we are seeing in the Midwest is unlikely to cause any yield loss at all because those plants are so far along," said John Rupe, a plant pathologist at the University of Arkansas. Once soybeans reach the R6 stage
and have developed full seeds, he added, "I don't think people have to worry about it." The Agriculture Department said on Monday [1 Oct 2007] that 29 per cent of the US soybean crop had been harvested, with Illinois and Iowa ahead of the national average with 43 per cent and 35 per cent, respectively.

Plant pathologists and soybean growers cited three keys to determining whether soybean rust will affect the Midwest and how severe it will be: if there is good over winter survival in the South, if weather allows the fungus to build up and spread in the 1st part of the growing season, and if the right weather conditions exist in the Midwest.

Greg Tylka, a plant pathologist at Iowa State University, who helps monitor more than 20 sentinel plots and 40 soybean fields for the fungus, said soybean rust spores make it to his state throughout the growing season, but
the right weather conditions have not been present to allow the disease to develop early in the year. "You could have a lot of spores show up and if you don't have the right moisture and temperature conditions the disease isn't going to develop," said Tylka. "It just takes the right series of events."

Soybean rust thrives under cloudy, warm, humid, and moist conditions. The 1st case of soybean rust was detected in the US mainland late in the 2004 growing season. Experts suspect Hurricane Ivan blew soybean rust spores
from South America. An outbreak one year does not mean major problems the next, since spores that blow into the Midwest die from the cold in the winter. Soybean rust can only survive in southern Florida or possibly the Gulf Coast. Over the past 2 years, few hurricanes have hit the United States hard enough to push the fungus north early in the season when the crop is most susceptible to yield loss.

"We were lucky to once again escape a major outbreak in the larger production areas in the Midwest," said Bob Callanan, a spokesman for the American Soybean Association. Still, he urged soybean growers to remain vigilant and learn more about the disease "because next year [2008] could be a whole different ballgame."

[byline: Christopher Doering]

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[The fungus _Phakopsora pachyrhizi_ was identified in Japan in 1902 as the cause of soybean rust. It can cause premature defoliation, with yield losses of up to 70 per cent reported on farms in Asia. It is widespread in Asia and Africa, but data are lacking concerning its establishment in Europe. The 1st detection of _P. pachyrhizi_ in the New World was in Paraguay in 2001, and it was introduced into the USA in 2004. It has a wide host range unusual for rust fungi, and besides soybean, a number of other species in the family of _Fabaceae_ can also be affected. Weed species, for example kudzu (Japanese arrowroot, _Pueraria lobata_) can serve as pathogen reservoirs, and spores are spread by wind over long distances. New strains of _P. pachyrhizi_ with increased virulence are emerging. Fungicides may be used in disease management and partially resistant soybean lines are available.

The system of soybean growth stages divides plant development into vegetative (V) and reproductive (R) stages. The vegetative stages are numbered according to how many fully developed trifoliate leaves are present. The reproductive (R) stages begin at flowering and include pod development, seed development, and plant maturation. The stages can overlap.

Maps
US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>
Current distribution of soybean rust in the US:
<http://www.sbrusa.net/>
Worldwide distribution of soybean rust (December 2005):
<http://www.eppo.org/QUARANTINE/Alert_List/fungi/maps/PHAKPA_map.htm>
Pictures of soybean rust symptoms:
<http://soybeanrust.unl.edu/soybean/siteImages/plantdate.gif> and via
<http://www.plantmanagementnetwork.org/search/image/search_action.asp?keyword=soybean+rust&type=all&imagetype=&B1=Submit> 

Links
Additional news stories:
<http://www.hpj.com/archives/2007/oct07/oct8/SoybeanrustarrivesinMissour.cfm>,
<http://www.hpj.com/archives/2007/oct07/oct8/AsiansoybeanrustdetectedinI.cfm>, 
and
<http://westohcropweather.blogspot.com/2007/10/soybean-rust-its-moving-to-north-oct-1.html> 

Information on soybean rust:
<http://www.aphis.usda.gov/plant_health/plant_pest_info/soybean_rust/background.shtml> 
and
<http://www.eppo.org/QUARANTINE/Alert_List/fungi/PHAKPA.htm>
Diagnostic fact sheet:
<http://nt.ars-grin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Phakopsorapachyrhizi> 

Disease history and background:
<http://www.apsnet.org/online/feature/rust/>
Rust background, tracking, and current information:
<http://www.stopsoybeanrust.com/> and
<http://www.sbrusa.net/>
_P. pachyrhizi_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=121037>
Description of soybean growth stages:
<http://extension.agron.iastate.edu/soybean/production_growthstages.html>. 
- Mod.DHA]

[see also in the archive:
Asian soybean rust - South Africa, USA (KS) 20070927.3197
Asian soybean rust - USA: northward spread 20070804.2527
Soybean rust, Asian strain, update 2007 (02): USA 20070618.1972
Asian soybean rust, kudzu - US (LA) 20070517.1567
Asian soybean rust, plant tissue - USA (IA) 20070410.1214
Soybean rust, Asian strain, update 2007 - USA 20070318.0952
Soybean rust, Asian strain, update 2006 - USA 20070317.0942
2006
---
Soybean rust, Asian strain, soybean - USA (KY): 1st report 20061017.2985
Soybean rust, Asian strain - USA (IL): 1st report 20061014.2948
2005
---
Soybean rust, Asian strain - USA: 2005 disease summary 20051228.3694
Soybean rust, Asian strain, kudzu control 20051006.2914
2004
---
Soybean rust - USA: 1st report 20041110.3043]


 

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