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[1] Asian soybean rust - USA (Oklahoma): 1st report
[2] Asian soybean rust - USA: 2007 summary and predictions

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[1] Asian soybean rust - USA (Oklahoma): 1st report
Date: 26 Jul 2007
Source: Stop Soybean Rust [edited]
<http://www.stopsoybeanrust.com/viewStory.asp?StoryID=1073>

Asian soybean rust was confirmed for the 1st time in Oklahoma on a leaf sampled from a sentinel plot in Bryan County on 13 Jul 2007, making Oklahoma the 8th state with rust this year [2007]. Soybeans in Choctaw County were found to have rust 2 days ago.

The 2 counties are in southeastern Oklahoma, directly across the border from rust-positive Fannin County in Texas and only 2 counties west of rust-positive Little River County in Arkansas. This is the farthest north soybean rust has been found in the U.S. this year [2007].

According to the Oklahoma state commentary that reported the finds
today: "Rust was found for the 1st time in Oklahoma on a sentinel plot sample taken on 13 Jul 2007 from Bryan Co. (south of Bennington) on one of 100 leaves sampled. By 23 Jul 2007, rust increased to an incidence of about 20 percent of sampled leaves in the sentinel plot.
On 23 Jul 2007, rust was also found in a nearby commercial field at an incidence level of 10 percent.

"In adjacent Choctaw County, rust was found in a commercial field (near Frogville) at an incidence of one percent on 24 Jul 2007. Rust has not been found in the sentinel plot, kudzu, and in other commercial fields in Choctaw County. Positive finds have been in soybeans at the R4 to R5 growth stages."

Sentinel plots in Atoka, Ottawa, Payne, Sequoyah, Tulsa, and Washington Counties remain negative for rust this week, the report said. Rust also has not been found in observational samples taken from commercial fields in Garvin, Pottawatomie and Le Flore Counties.

"While rains have subsided, conditions remain favorable for rust development this week with moderate daytime temperatures, high humidity and night time dews," according to the commentary. "Other diseases, such as downy mildew, brown spot, bacterial blight, and frogeye leaf spot, are widespread and make rust recognition difficult."

Oklahoma officials said fungicide sprays are recommended to protect soybeans from rust in affected counties and nearby counties to the north when soybeans are in the R1 to R5 growth stages. The decision to spray at late R5 is a judgment call. Check soybeans periodically and submit suspect samples to local County Ag Educators for submission to the OSU Plant Disease and Insect Diagnostic Laboratory.
As of 26 Jul 2007, early maturing varieties (MG3 and MG4) are at R3 to R5 growth stages in Oklahoma, while full-season varieties (MG5 and MG6) are at various vegetative stages.

These finds bring the U.S. total of counties and parishes with soybean rust in 2007 to 45 in 8 states: Texas 15, Florida 10, Louisiana 6, Alabama 5, Georgia 5, Oklahoma 2, Arkansas 1, Mississippi 1.

On this date last year [2006], only 26 counties and parishes in 5 states had soybean rust, and it had gone no farther west than Rapides Parish, Louisiana and no farther north than Montgomery County, Alabama.

Source: Oklahoma state commentary and historical data on <http://www.sbrusa.net>.

[Byline: Marilyn Cummins <StopSoybeanRust.com> 
 
--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator
<dodds@ucr.edu>

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[2] Asian soybean rust - USA: 2007 summary and predictions
Date: 26 Jul 2007
Source: Stop Soybean Rust [edited]
<http://www.stopsoybeanrust.com/viewStory.asp?StoryID=1072>

During the last 2 seasons, we projected that the risk of soybean rust (SBR) was no longer a concern when June ended. This season is different from last year [2006], because we received more rain early in the growing season, and the disease progressed much faster in the South than during the last 2 years.

Below is an update on the movement of SBR in the 2 northward pathways and an outlook for the rest of the growing season.

Eastern region and Mississippi River pathway

For the southeastern region, SBR is progressing slowly due to the dry conditions from spring into early summer. The spores from that region will no longer be a threat to soybean production areas west of the Appalachian Mountains because of prevailing winds this summer [2007].

In Louisiana, since the detection of soybean rust in the central part of the state (a month earlier than last year [2006]), no new northward development has been reported. Into July 2007, SBR in Louisiana will not be a concern as a source of spore production because the weather will be too hot for soybean rust development. However, there is a good possibility that spores were blown to regions north of Louisiana before July 2007, as suggested by our
computer models.

Western pathway

SBR was found in northern Texas in several counties last week. It was said to be widespread in northern Texas, based on their Web reports, and fungicide application has been recommended in that area.

During Monday's national teleconference, more SBR was reported in northern Texas, and the disease also was found in southwestern Arkansas in the area next to northeastern Texas. The possibility of SBR occurrence in northern Texas had been predicted by computer models for the week after 19 May 2007. If the spores landed in that timeframe, it took a month for the disease to develop to detectable levels and a few more weeks to achieve a widespread level.

Computer prediction maps also suggested that spore clouds had spread to Oklahoma in early June 2007, and there were plenty of rains from  spring to early summer, setting the stage for soybean rust development.

Outlook

The occurrence of soybean rust in northern Texas increases the possibility for viable spores to spread to northern production regions. Computer models suggest that soybean rust spores could be blown as far north as central Illinois in August 2007 in an effective concentration.

It is likely that more soybean rust will be found north of Texas in the western pathway of soybean rust during the remainder of the season. An increase in disease intensity in this pathway should increase the possibility of spore movement to Iowa, especially to southeastern Iowa. We need to watch the situation closely, because favorable conditions are predicted in that region for the next 30 days.

With the current information, the risk of having an SBR outbreak in Iowa severe enough to reduce soybean yield is low to moderate for the rest of the growing season, as suggested by our latest computer predictions. Average precipitation has been predicted for Iowa and surrounding states for the next 30 days by the National Oceanic and
Atmospheric Administration Climate Center. Our computer model also predicts that there is less than 40 percent favorability for the occurrence of soybean rust in the next 30 days.

We will continue to monitor the occurrence of SBR in the South and in the western pathway, and update our outlook as new developments arise.

[X. B. Yang is a professor of plant pathology with research and extension responsibilities in soybean diseases at Iowa State University. Zaitao Pan is an assistant professor and a climatologist at St. Louis University. This article originally appeared on page 237 of the IC-498(20), 23 Jul 2007 issue, posted on Iowa State's Integrated Crop Management site - Mod.DHA]

[Byline: By X. B. Yang, Iowa State, and Zaitao Pan, St. Louis University]

--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator
<dodds@ucr.edu>

[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 percent 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. New strains of _P. pachyrhizi_ with increased virulence are emerging, and weed species can serve as pathogen reservoirs.

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. The stages above are: R1 - beginning of flowering; R3 - beginning of pod development; R5 - beginning of seed set.

The other soybean diseases mentioned are: frogeye leaf spot which is caused by the fungus _Cercospora sojina_ and can infect leaves, stems, and seeds of soybean; downy mildew which is caused by the fungus _Peronospora manshurica_; bacterial blight caused by _Pseudomonas syringae_ pv. _glycinea_ or _P. savastanoi_ pv. _glycinea_ (there is still some debate whether these are distinct species or different strains of _P. syringae_); and brown spot which is a fungal disease caused by _Septoria glycines_.

Maps
US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>
Oklahoma:
<http://geology.com/state-map/oklahoma.shtml>
Oklahoma counties:
<http://geology.com/county-map/oklahoma.shtml>
Current distribution of soybean rust in the US:
<http://www.sbrusa.net/>
Worldwide distribution of soybean rust up until December 2005:
<http://www.eppo.org/QUARANTINE/Alert_List/fungi/maps/PHAKPA_map.htm>

Pictures
Soybean rust symptoms on soybean:
<http://soybeanrust.unl.edu/soybean/siteImages/plantdate.gif>  and via
<http://www.plantmanagementne2rk.org/search/image/search_action.asp?keyword=soybean+rust&type=all&imagetype=&B1=Submit>
Symptoms of all other soybean diseases via:
<http://www.ent.iastate.edu/imagegal/plantpath/soybean/>

Links
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>
Soybean frogeye information:
<http://extension.agron.iastate.edu/soybean/diseases_frogeye.html>  and
<http://www.ces.ncsu.edu/depts/pp/notes/Soybean/soy003/soy003.htm>
_C. sojina_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=119516>
Soybean downy mildew information:
<http://plantpathology.tamu.edu/Texlab/Fiber/Soybean/sbdm.html>
_P. manshurica_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=270522>
Soybean bacterial blight information:
<http://www.lgseeds.com/LG_Tech2/soy_bacterialblight.asp>
_Pseudomonas_ taxonomy and species list:
<http://www.bacterio.cict.fr/p/pseudomonas.html>
Soybean brown spot and bacterial blight information:
<http://www.ipm.iastate.edu/ipm/icm/1996/7-8-1996/soyfoldis.html>
_S. glycines_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=215541>
Description of soybean growth stages:
<http://extension.agron.iastate.edu/soybean/production_growthstages.html>.
- Mod.DHA]

[see also in the archive:
Frogeye leaf spot, soybean - USA: surveillance 20070627.2067
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
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Soybean rust, Asian strain, soybean - USA (KY): 1st report 20061017.2985
Soybean rust, Asian strain - USA (IL): 1st report 20061014.2948
2005
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Soybean rust, Asian strain - USA: 2005 disease summary 20051228.3694
Soybean rust, Asian strain, kudzu control 20051006.2914
2004
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Soybean rust - USA: 1st report 20041110.3043
2002

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