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: 11 Jun 2009
Source: Country Guide [edited]
<http://www.country-guide.ca/East/issues/ISArticle.asp?aid=1000330463&PC=FBC&issue=06112009>

Ontario's oat growers will need to be "on the alert" this spring [2009] for crown rust, as fungal infection rates are high this spring in the other plant species that host the rust spores. Crown rust depends on European buckthorn as the alternate host, and buckthorn infection rates are high this spring in many parts of the province, crop plant pathologist Albert Tenuta said.

The pathogen is not seed or soil-borne, Tenuta said. European buckthorn is the primary local source of spores, while another source is blown in from the southern U.S. There are different races of the crown rust fungus, and like other rusts, they change over time, Tenuta said. Thus, they can affect a variety's performance over time.

Crown rust, he said, is most problematic when the disease develops early. Temperatures above 30 C, which stop infection, are expected soon, but the milder daytime highs (15-25 C) and nighttime lows (10-20 C), combined with frequent dew and rain in the meantime, have not helped the situation.

To deter crown rust, the province advises oat growers to seed a tolerant variety and as early as possible in the season to avoid late-season infections. Foliar fungicides are effective against the pathogen but must be applied "in a timely manner" and close to flag leaf emergence so as to protect the flag leaf, Tenuta said.

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[Crown rust of cultivated or wild oats (_Avena_ species) is caused by the fungus _Puccinia coronata_. While it can infect a number of grasses, particularly ryegrass, the strains on grasses do not cross into oats. Rye and barley may be slightly affected by crown rust, but these strains will also not infect oats. Pustules containing orange spores are produced on leaves and sheaths, and these are spread by wind and by mechanical means. The life cycle of _P. coronata_ includes as obligate alternate hosts buckthorn (_Rhamnus catharticus_) or alder buckthorn (_Frangula alnus_) before it can infect oats again.

The disease is favored by warm and humid weather and mild winters.
Severe epidemics have been reported with yield losses of up to 40 percent. Disease management may include timely fungicide applications, cultural methods (for example early planting), use of resistant oat varieties, and eradication of buckthorn within approximately 2 km of oat fields.

Maps
Canada:
<http://www.lib.utexas.edu/maps/americas/canada_pol_1986.gif> and <http://healthmap.org/promed?v=55.4,-101.9,4>
Ontario:
<http://atlas.nrcan.gc.ca/site/english/maps/reference/provincesterritories/ontario/referencemap_image_view>

Pictures
Oat crown rust on oats:
<http://ipm.illinois.edu/bulletin/photos/oat_crown_rust.jpg>  and <http://www.ars.usda.gov/images/docs/9919_10113/ocr.jpg>
Symptoms on buckthorn:
<http://ipm.illinois.edu/bulletin/photos/buckthorn_oat_rust.jpg>

Links
Information on oat crown rust:
<http://www.ars.usda.gov/Main/docs.htm?docid=9919>,
<http://www.hgca.com/minisite_manager.output/3668/3668/Cereal%20Disease%20Encyclopedia/Diseases/Crown%20Rust.mspx?minisiteId=26>
and
<http://ipm.illinois.edu/diseases/series100/rpd109/index.html>
_P. coronata_ taxonomy and synonyms:
<http://www.indexfungorum.org/names/SynSpecies.asp?RecordID=143930>
- Mod.DHA]