May 2, 2006
From: ProMED-mail<promed@promedmail.org>
Source: USDA Cereal Rust Bulletin 2006: Number 04, 2 May 2006 [edited] <http://www.ars.usda.gov/Main/docs.htm?docid=9757>


Most of the winter wheat crop is in fair condition and ahead of normal crop development throughout the United States. Throughout much of the northern spring grain area rain has delayed fieldwork.

Wheat stem rust. On 18 Apr 2006, wheat stem rust was at low levels in plots at Baton Rouge, Louisiana. These plots of wheat were drying down 14 days earlier than normal because of minimal rainfall. There have been no other reports of wheat stem rust in the U.S.

Wheat leaf rust. In late April, plots of susceptible wheat cultivars had leaf rust severities up to 80 percent, in the area from central Texas, central Mississippi to central Georgia. Fields in the same area had severities from 0 to 10 percent (Fig. 1). Drier than normal conditions in March and April slowed rust development throughout much
of the southern U.S. On 1 May, traces of leaf rust were found in
plots at Stillwater in northeastern Oklahoma. The wheat is at the milk stage of maturity and therefore it is too late for rust to cause high yield losses this year. In late April, traces of leaf rust were found in south central Kansas. In this area wheat was under extreme drought stress and at heading to early flowering growth stage. In late April, plots of susceptible wheat cultivars in northeastern Louisiana had leaf rust severities up to 80 percent on flag leaves.
Leaf rust severity will increase significantly with the warmer temperatures. In late April, plots in e!
ast central Arkansas had 0-50 percent leaf rust severities. In this area rainfall has been at normal levels. Leaf rust should continue to increase and provide inoculum for the northern wheat growing area.

Wheat stripe rust. In late April, hot and dry conditions slowed any stripe rust development in plots and fields throughout the southern U.S. (Fig. 2). For example, in central Texas and northeastern Louisiana plots stripe rust infections were observed but there was little sporulation occurring. During 2005 there was more stripe rust because the cooler than normal temperatures in the last 2 weeks of April were more conducive for stripe rust development in the southern U.S. In late April, severe stripe rust was observed in late maturing susceptible cultivars in the nursery at Plains in southwestern Georgia. In the nursery most of the stripe rust infections had occurred earlier in March and April when temperatures were cooler. By late April leaf rust was the most prevalent rust on wheat at Plains. On April 26, light amounts of stripe rust were reported on winter wheat in plots at St. Paul, Minnesota. This was most likely from an over wintering infection. By the 3rd week in April, susceptible entries in winter wheat nurseries at Mount Vernon in northwestern Washington had 60 percent levels of stripe rust infection. In south central and southeastern Washington, early planted winter wheat fields had 5 percent stripe rust severity. In this area the initial stripe development was much later than in 2005, but about normal for this area.

--
ProMED-mail
<promed@promedmail.org>

[There are 3 main rust diseases of the cereal crop plant wheat (bread wheat, _Triticum aestivum_ and durum wheat, _Triticum turgidum_), all caused by species of the fungus Puccinia: wheat stem rust (_P. graminis f.sp. tritici_), wheat leaf rust (_P. triticina_ aka _P. recondita f. sp. tritici_) and wheat stripe rust (_P. striiformis f. sp. tritici_).

Severe losses due to wheat stem rusts have abated in the USA since the 1960s due to effective resistance breeding. Severe losses are still a possibility with leaf rust. The USDA Cereal Disease Laboratory in St. Paul, MN publishes regular reports on cereal rusts in the USA during the crop season. Each report gives detailed state-by-state information, including a summary map, all in pdf file format (see link to main article).

In this the 4th bulletin for 2006 it is noted that wheat leaf rust is widespread and increasing in severity throughout the southern U.S.
Leaf rust should continue to increase and provide inoculum for the northern wheat growing area. Last year [2005] there was more stripe rust in the southern U.S in April than in 2006 because the cooler than normal temperatures in the last 2 weeks of that month were more conducive for stripe rust development.

Map:
Puccinia spore pathway
<http://www.ars.usda.gov/Main/docs.htm?docid=11301>
Wheat in USA
<http://www.nass.usda.gov/research/atlas02/Crops/Field%20Crops%20Harvested/Wheat/All%20Wheat%20for%20Grain,%20Harvested%20Acres-chor.gif>

Pictures:
Wheat leaf rust
<http://www.cdl.umn.edu/nomenclature/inf_set.jpg>
Wheat stem rust
<http://www.gov.mb.ca/agriculture/crops/diseases/images/fac15s01.jpg>
Wheat stripe rust
<http://www.utextension.utk.edu/fieldCrops/wheat/Wheat_photos/Wheat_StripeRust.jpg>

Links:
<http://www.ars.usda.gov/Main/docs.htm?docid=9854>
- Mod.JAD]

[see also in the archive:
Cereal Rust Update - USA (03) 20060418.1144
Cereal Rust Update - USA (02) 20060404.1012
Cereal rust update - USA 20060322.0895]