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International Society for Infectious Diseases <http://www.isid.org>

Date: Wed 11 August 2008
Source: KOLNKGIN [edited]
<http://www.kolnkgin.com/news/headlines/26846789.html>

Rust damages state's corn crop

Plant experts are warning Nebraska farmers to check their fields for a potentially devastating corn disease. In 2006, southern rust hit south central Nebraska, causing a 30 percent loss in yield. Now the disease is back. "It causes a lot of injury to the leaves, and when you injure the leaves, it competes with grain fill," said Tamra Jackson, UNL [University of Nebraska- Lincoln] Extension Plant pathologist.

But experts are more concerned about another rust that's, well, more common. "Common rust is very widespread throughout the state right now. We actually are having an even bigger problem in the southwest part of the state where they're treating a lot of fields [with fungicides] and they've never had to do that before," Jackson said.
Some treatments cost around [USD] 20 per acre.

"We had a lot of rain earlier in the season that delayed planting.
The late-planted fields are at a higher risk for disease and for the damage caused by those diseases," Jackson said. That rainy and cool weather caused the increase in rust. "The spores that cause the infection actually have to blow in from southern states every year, and since we had a lot of moisture earlier in the season, we've got a lot more rust diseases," she said. Jackson said warmer weather could help kill common rust but would help southern rust grow.

[Byline: Sara Geake]

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Communicated by:
ProMED-mail
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[_Puccinia polysora_ causes southern rust (also called polysora or tropical rust) in maize. The fungus occurs in most tropical and subtropical regions and can cause significant losses of over 50 percent. Southern rust is favoured by warm, humid conditions. Leaves may die prematurely reducing photosynthetic ability, and therefore infection before grain fill has been completed is more damaging to yield than infection late in the crop cycle. _P. polysora_ needs living host tissue for survival and spores are wind dispersed. No alternate hosts of the fungus are known. Resistant or tolerant ('slow rusting') varieties are being developed.

Common rust of maize is caused by the related species _Puccinia sorghi_. The disease is found worldwide in cooler temperatures and high humidity. Rust development is much more likely in pre-tassel stage plants because a large whorl provides a humid environment, and young leaf tissue is more susceptible to infection than emerged leaves. Resistant maize varieties are available. This fungus can also affect _Oxalis_ species as alternate hosts [_Oxalis_ is the largest genus in the wood sorrel family Oxalidaceae, with approx. 800 species worldwide. - Mod.JW]

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>

Pictures
Southern rust symptoms:
<http://www.ipm.iastate.edu/ipm/icm/node/2596>
Southern rust, photo gallery:
<http://www.ent.iastate.edu/imagegal/plantpath/corn/southrust/>
Common rust symptoms:
<http://www.ipm.iastate.edu/ipm/icm/node/2594>
Common rust, photo gallery:
<http://www.ent.iastate.edu/imagegal/plantpath/corn/comrust/>

Links
Additional news stories:
<http://www.kptm.com/Global/story.asp?S=8812976&nav=menu606_2>  and <http://www.cattlenetwork.com/Content.asp?ContentID=241813>
Information on southern and common rusts of maize:
<http://edis.ifas.ufl.edu/BODY_VH051>  and <http://www.dpi.qld.gov.au/cps/rde/xchg/dpi/hs.xsl/26_4721_ENA_Print.htm>
Information on common rust:
<http://www.lgseeds.com/lg_tech2/commonrust.asp>
_P. polysora_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=179511>
_P. sorghi_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=194826>
UNL Plant Pathology Extension:
<http://plantpathology.unl.edu/Extension.html>.  - Mod.DHA]