A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>

Date: 7 October 2008
Source: Delta Farm Press [edited]
<http://deltafarmpress.com/soybeans/louisiana-yields-1009/>

The outlook for soybeans across the state is mixed. LSU [Louisiana State University] AgCenter's soybean specialist Ronnie Levy says the rains that accompanied hurricanes Gustav and Ike kept farmers from spraying for disease and insects in a timely manner. Diseases have been a problem in fields across the state.

Cercospora has appeared in many fields. In other fields, farmers are dealing with green bean syndrome, a problem that occurs when soybean plants won't mature. Levy said Asian soybean rust has been identified on soybeans across the state, including at the LSU AgCenter's Dean Lee Research Station. "Once again, soybean rust came in at the point where most soybeans won't be affected," Levy said. "We've seen this for several years. We haven't had a real problem from rust because people are using fungicides to help control it."

--
Communicated by:
ProMED-mail <promed@promedmail.org>

[Two species of the fungal genus _Cercospora_ are known to affect soybean: Frogeye leaf spot, caused by _C. sojina_, which can infect leaves, stems, and seeds causing significant yield losses of 10 to 50 percent (more info on frogeye is available via ProMED-mail post no. 20070627.2067); and leaf spot due to _C. kukuchii_, which causes blight and purple seed stain. Both diseases are favored by warm temperatures and high humidity, and the report above does not state which one has been sighted.

The name green bean syndrome (GBS) is associated with plants that never seem to reach maturity. It is not well understood yet, but it is attributed to a combination of factors. Stinkbugs (insects in the order _Hemiptera_) may be associated with it, and it is suggested that they may transmit a phytoplasma involved in GBS. Aerial blight caused by the fungus _Thanatephorus cucumeris_ has also been reported associated with GBS. _T. cucumeris_ is a ubiquitous soilborne fungus that causes different root and fruit rots in a large number of crops (see 2007 ProMED-mail posts listed below).

Asian soybean rust (ASR) is caused by the fungus _Phakopsora pachyrhizi_. It can cause premature defoliation with yield losses of up to 70 percent and was introduced into the USA in 2004. It over-winters in southern regions, and spores are being carried northwards every season. More information on ASR can be accessed via ProMED-mail post no. 20080928.3070 and the links below.

Maps
USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html>  and
<http://healthmap.org/promed?v=40,-97.6,4>
US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>
Current distribution of soybean rust in the US via:
<http://www.sbrusa.net/>

Pictures
Frogeye symptoms, upper leaf surface:
<http://www.ces.ncsu.edu/depts/pp/notes/Soybean/soy003/frogeye2.jpg>
Frogeye symptoms, leaf underside:
<http://extension.missouri.edu/explore/images/g04442frogeyebottom.jpg>
_C. kukuchii_ leaf spot:
<http://www.ipm.iastate.edu/ipm/icm/files/images/cercospora.jpg>
ASR symptoms on soybean:
<http://www.ent.iastate.edu/images/plantpath/soybean/asianrust/asian_soyrust_lesions.jpg> 
(leaf lesions),
<http://soybeanrust.unl.edu/soybean/siteImages/plantdate.gif>  (whole plant)
Stinkbug:
<http://www.ent.iastate.edu/imagegal/hemiptera/stinkbug/3938.1stinkbug.html>

Links
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. kukuchii_ leaf spot information:
<http://extension.agron.iastate.edu/soybean/diseases_cercosporasojina.html>
Overview of disease due to _Cercospora_ species:
<http://www.oisat.org/pests/diseases/fungal/cercospora_leaf_spot.html>
Soybean green bean syndrome information:
<http://deltafarmpress.com/mag/farming_causes_green_bean/>  and
<http://deltafarmpress.com/mag/farming_green_bean_syndrome/>
Information on soybean rust:
<http://www.eppo.org/QUARANTINE/Alert_List/fungi/PHAKPA.htm>  and
<http://www.aphis.usda.gov/plant_health/plant_pest_info/soybean_rust/background.shtml>
Taxonomy of all fungal pathogens via:
<http://www.indexfungorum.org/Names/Names.asp>
LSU AgCenter:
<http://www.lsuagcenter.com/>
- Mod.DHA]