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: Wed 15 Jul 2008
Source: Stock & Land [edited]

Queensland and northern New South Wales growers need to be vigilant for stripe rust detection in grain crops following July's cool, wet climatic conditions. Queensland Department of Primary Industries (DPI&F) officers are issuing the alert after stripe rust infestations have been reported from central and southern NSW, and more recently at northern centres of Moree and Walgett.

DPI&F wheat industry development officer, Ann-Maree Bach, says the NSW rust infestations have an important bearing on disease management for northern growers. "Early stripe rust detection should raise industry-wide concern and growers may need to plan for control strategies," she said. "Stripe rust infections as early as this could lead to serious economic losses."

Ms Bach said recent weather is providing optimum conditions for stripe rust infection, and growers need to be aware of the potential threat that it may pose on their properties. "It is critical this season [2008] that growers in Queensland begin monitoring for stripe rust and other foliar disease, such as yellow spot, before growth stage 30 to allow enough time to protect the plant before damage is done to the flag leaf," she said.

Ms Bach said the earlier the infection the more damage the disease could cause. "The most damage is caused when the flag leaf and the 2 leaves below (the primary factories for yield and quality of the wheat plant) are infected," she said. "If stripe rust is present, fungicide management may be required on properties that have wheat varieties with stripe rust ratings less than "Moderately Resistant (MR)."

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[Wheat stripe rust (also called yellow rust) is caused by the fungus _Puccinia striiformis_ var. _striiformis_ and occurs worldwide mostly in cooler climates. It causes yellow leaf stripes, stunting of plants, and reduced grain number and size on developing heads. Yield losses may vary from 40 up to 100 per cent. It affects wheat, some barley varieties, triticale (wheat/rye hybrids), and a number of grass species. Spores are wind dispersed in several cycles during the cropping season. The fungus needs living plants to survive between seasons, it cannot survive on seed, stubble, or in soil. Volunteer plants may generate a "green bridge"
providing inoculum to infect new crops.

Disease management strategies include the use of resistant varieties, fungicide applications and control of volunteer wheat plants. Since the fungus interferes with seed development, infection early in the crop cycle is more damaging than infection after seed fill has concluded. Early discovery of infection at any stage of the crop cycle is important so action can be taken to limit the spread of the pathogen as well as build-up of inoculum.

The Australian Cereal Rust Control Program monitors the occurrence of cereal rust pathotypes each year and in 2003, for example, 6 pathotypes of stripe rust were identified throughout Australia. New strains are emerging worldwide (see previous ProMED-mail posts below) which may overcome major stripe rust resistance genes used in wheat breeding and potentially pose serious problems to farmers.

Yellow spot (also called tan spot) is caused by the fungus _Pyrenophora tritici-repentis_. It survives in wheat and occasionally triticale stubble.
Severe yellow spot may result in short, spindly plants with reduced tillering and root development. Where conditions are favourable, plants may be fully defoliated soon after flowering.

Maps
Australia:
<http://www.ga.gov.au/image_cache/GA4073.jpg>
NSW:
<http://www.ozhorizons.com.au/nsw/map.htm>
Queensland:
<http://www.ozhorizons.com.au/qld/map.htm>
Pictures
Stripe rust leaf symptoms on wheat:
<http://www.ars.usda.gov/Main/docs.htm?docid=9918&pf=1&cg_id=0>  and <http://utextension.tennessee.edu/fieldCrops/wheat/Wheat_photos/Wheat_StripeRust.jpg> 

Stripe rust symptom comparison on resistant and susceptible wheat cultivars:
<http://www.oznet.ksu.edu/path-ext/factSheets/wheat/Wheatimages/wheats1.jpg>
Wheat yellow spot symptoms:
<http://www.dpi.qld.gov.au/images/Biosecurity_GeneralPlantHealthPestsDiseaseAndWeeds/Wheat-YellowSpot-168.jpg>
and
<http://www.ksda.gov/includes/images/plant_protection/Plant%20Disease/TanSpotWheat117.jpg> 

Links
Information on wheat stripe rust:
<http://pnw-ag.wsu.edu/smallgrains/Stripe%20Rust.html>,
<http://www.ars.usda.gov/Main/docs.htm?docid=9918&pf=1&cg_id=0> and <http://www.oznet.k-state.edu/path-ext/factSheets/Wheat/Wheat%20Stripe%20Rust.asp> 

Stripe rust management:
<http://www.grdc.com.au/uploads/documents/striperustmgt.pdf>
_P. striiformis_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=427989>
Information on yellow spot disease of wheat:
<http://www.dpi.qld.gov.au/cps/rde/dpi/hs.xsl/26_7462_ENA_HTML.htm>  and <http://www.ag.ndsu.edu/pubs/plantsci/smgrains/pp766w.htm>
_P. tritici-repentis_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=255190>.  - Mod.DHA]