April 18, 2006
From: ProMED-mail<promed@promedmail.org>
Source: USDA Cereal Rust Bulletin 2006: Number 03, 18 Apr 2006 [edited] <http://www.ars.usda.gov/Main/docs.htm?docid=9757>


- Wheat stem rust is present in south central Louisiana plots.
- Wheat leaf rust is widespread throughout the southern U.S.
- Wheat stripe rust is at low levels in the U.S. except for Louisiana and California.

Winter wheat growth and development is ahead of normal crop development, but many areas in the southern U.S. are dry and need rain. In the spring wheat and oat area of the northern plains, warm temperatures have allowed for an early start of fieldwork and planting.

Wheat stem rust

In mid-April, soft red winter wheat plots at Crowley, in south central Louisiana, had stem rust severities of 40 percent. Stem rust was found in 28 of the 102 plots that are located near rice paddies. The regular dew formation in these plots provided a suitable environment for stem rust infections. This is the first report of wheat stem rust in U. S. this year.

Wheat leaf rust

By the 2nd week of April, susceptible cultivars like Jagelene and Jagger in nurseries at Castroville and College Station, Texas had 80 percent leaf rust severities. In highly resistant cultivars like Fannin and Endurance, no infections were found. Only low levels of rust have been reported in southern and central Texas fields because of the dry conditions. By early April, low levels of leaf rust have
been reported in Oklahoma. During the 2nd week of April, plots in
southern Louisiana had leaf rust severities up to 70 percent. In
early April, leaf rust was found on the lower leaves of the most susceptible cultivars in southwestern and south central Georgia. By mid-April, leaf rust was found in areas of Arkansas that had sufficient moisture. Leaf rust incidence and severity will increase in the next few weeks with periodic rainfall and dews throughout the
southern U.S. From rust collections made in early November in north
eastern Oklahoma plots, the following leaf rus!
t races were identified: TBBJ (Lr2a virulence), TDBJ (Lr24 virulence) and TDDS (Lr17 & 24 virulence). From collections made in early December in central Texas, the TDBJ (Lr24 virulence) race and in northwest Arkansas the TBRK (Lr 11 & 18) race were identified. These leaf rust races also were identified from rust collections made during the 2005 survey (<http://www.ars.usda.gov/mwa/cdl>).

Wheat stripe rust

In early April, only traces of stripe rust were found in southern and central Texas (Fig. 2). Weather conditions have not been favorable for rust development (limited moisture, warm nights and high daytime temperatures). As of early April, no stripe rust has been found in
Oklahoma or states to the north. In early April, no stripe rust had
been found in wheat plots in southern Louisiana while high levels of stripe rust were observed in northeast Louisiana plots. By early April, stripe rust was increasing throughout Arkansas, but conditions did not favor development of high rust severities. In early April, stripe rust was found in southern Georgia. Wheat stripe rust infection in the southern Great Plains and southeastern U.S. is at a much lower level than last year on this same date. If conditions remain unfavorable for rust development a reduced amount of inoculum is expected for the northern regions of the U.S. For the past month California has had cool and very wet conditions, which have been favorable for stripe rust development. In early April, the susceptible forage wheat cultivar Dirkwin had stripe rust severity of 30 percent in the Imperial Valley. Infections also were noted in fields of Orita durum wheat in the Imperial Valley. Light infections of wheat stripe rust were reported in the southern portion of the San Joaquin Valley and more severe infections were reported from scattered areas further north in the San Joaquin Valley and throughout the Sacramento Valley. In some Sacramento Valley fields,
80 percent severities were found in hot spots. By the 2nd week of
April, nursery plots at Mt. Vernon (northwestern Washington) had 40 percent stripe rust severity. Rust also was found in some surrounding fields. Wheat stripe rust was not found from central to eastern Washington during the second week in April. Stripe rust will develop later this year then last in most of the wheat and barley producing areas in the eastern Pacific Northwest.

--
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).

The third bulletin for 2006 contains the first report of wheat stem rust in the USA this year, at Crowley in south central Louisiana. No new races of leaf rust have been identified yet when compared to 2005. Unusually cold and wet weather in California has favored stripe rust.

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 (02) 20060404.1012 Cereal rust update - USA 20060322.0895]