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Date: Mon 6 Apr 2009
Source: NSW Department of Primary Industries [edited]
<http://www.dpi.nsw.gov.au/aboutus/news/recent-news/agriculture-news-releases/rust-alert>

Rust alert for North Coast soybean growers

An outbreak of the foliar disease leaf rust is threatening the North Coast's bumper soybean crop due to be harvested in coming weeks, according to NSW Department of Primary Industries (DPI). With 13 000 hectares [32 124 acres] of soybeans planted between Macksville and Tweed Heads and a near record 36 000 tonne crop waiting to finish off, growers are being advised to monitor their crops for rust and treat if necessary and possible.

NSW DPI Grafton-based research agronomist Natalie Moore said the current cool, rainy weather was favourable for rust growth, which was a concern with harvest so close. "If left unchecked, the rust can prematurely defoliate the soybean plants and significantly reduce seed size and tonnage. Growers need to protect the green leaf on the plant now, especially in the late-planted crops where the pods have not yet finished filling. The green leaf plays a critical role in making sure the pods fill to achieve yield potential."

Dr Moore said growers were looking towards a good harvest after last year's crop was hit hard by flooding rains, especially in the Richmond Valley and then leaf rust. "Some crops were set back this season due to the hot dry conditions in January [2009] and late planting -- so there is a fair bit riding on this harvest." Dr Moore said growers should assess the stage of their crop -- and determine whether they have enough green leaf to finish the pods. "If crops have 5 weeks to run and the current wet conditions continue, growers need to protect the green leaf with a rust treatment as soon as they can get back on their paddocks," she said.

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[Leaf rust (also called soybean rust, Asian rust) caused by the fungus _Phakopsora pachyrhizi_ can result in yield losses of soybean crops of up to 70 percent. It is widespread in Asia and Africa and spreading in the Americas, but data are lacking on its establishment in Europe. Besides soybean, over 30 other species in the family of _Fabaceae_ can also be affected and may serve as pathogen reservoirs.
Spores are spread locally by splashing rain, or by wind over long distances. Fungicides may be used in disease management, and partially resistant soybean lines are available. However, new fungal strains with increased virulence and fungicide resistances are emerging.

A related, but less virulent species (_P. meibomiae_) is found in South America and the Caribbean causing similar symptoms.

Maps
Australia:
<http://www.ga.gov.au/image_cache/GA4073.jpg> and <http://healthmap.org/r/008Y>
NSW:
<http://www.ozhorizons.com.au/nsw/map.htm>

Pictures
Leaf rust on soybean:
<http://www.ent.iastate.edu/images/plantpath/soybean/asianrust/asian_soyrust_lesions.jpg>
and
<http://www.state.nj.us/agriculture/plant/soybeanrust.jpg>
Electron microscopy of leaf rust spores:
<http://www.wbhm.org/pics/features/soybean-spores.jpg>

Links
Information on soybean rust:
<http://www.eppo.org/QUARANTINE/Alert_List/fungi/PHAKPA.htm> ,<http://ohioline.osu.edu/ac-fact/0048.html>,
and
<http://nt.ars-grin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Phakopsorapachyrhizi>
Disease history and background (with pictures):
<http://www.apsnet.org/online/feature/rust/>
_P. pachyrhizi_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=121037>  - Mod.DHA]

[see also in the archive:
2008
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Soybean diseases - USA: (LA) 20081012.3231 Asian soybean rust - USA, Mexico: update 20080928.3070
2007
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Asian soybean rust - USA: 2007 final report 20071230.4184 Asian soybean rust - Canada: 1st report, (ON) 20071120.3751 Asian soybean rust - Congo DR: 1st report 20070917.3086 Asian soybean rust - Ghana: 1st report 20070820.2710
2006
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Soybean rust - Mexico: 1st report 20060219.0546
2005
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Soybean rust, Asian strain - Americas: alert 20050528.1476
2004
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Soybean rust - USA: 1st report 20041110.304 and older items in the archives]