ISSUE 2   May 22, 2008

SOYBEAN RUST SUMMARY FOR 2007

Soybean rust was detected in 19 states and 1 Canadian province (Ontario) in 2007. The disease was reported in more states and spread further north (Northern Iowa) than any other year since it was introduced to the United States in 2004.

Despite the occurrence of the disease in many states, the spread of rust in 2007 will have no impact on soybean rust spread in 2008. Soybean rust canít survive the winter, so with the exception of a few locations along the gulf coast, all disease in the United States had died by spring. Therefore, for rust to cause problems, it must spread north again from one these overwintering sites.

Soybean rust summary map
Map of soybean rust spread in United States
and Canada in 2007, available at www.sbrusa.net
Counties with green are counties in which soybean
rust was scouted for and not found, counties with
red are counties in which soybean rust was scouted
for and found, counties with red hashes are counties
in which soybean rust was scouted for and found,
but has since died.

 

SOYBEAN RUST ACTIVE IN TEXAS

Monitoring for soybean rust in 2008 has been underway in the United States and Mexico since January. As expected, most of the soybean rust was killed by the winter temperatures. However, a few pockets of the disease are still active, including a small area in east central Texas. To put this in perspective, soybean rust was not found in Texas until mid-June last year, so the disease is about one month ahead of where it was last year.

The good news is that soybean rust in Texas is struggling. Texas has been very dry, not quite as dry as western North Dakota perhaps, but dry nonetheless. The soybean rust pathogen needs ample rain or dew to spread to other plants, and in dry conditions, spread is severely hampered. Even if the disease was spreading actively, Texas is a long way from North Dakota, so there is nothing to worry about at this point.

Soybean rust will be monitored throughout the United States again this summer. All information is fed into a website, available at www.sbrusa.net. I encourage those of you interested to visit the site. Soybean rust information and monitoring updates are included weekly.

We wonít begin our scouting efforts in North Dakota for another 3-4 weeks, but will soon be locating fields to monitor as Ďsentinelí plots. Sentinel plots are simply small areas in a field that are intensively sampled each week throughout the growing season. If we find something interesting (rust or otherwise), we will let you know.

Soybean rust map
Map of soybean rust in the United States
as of May 19, 2008, available at www.sbrusa.net
Note: although soybean rust is prevalent in
Florida, the spreading patterns make Florida
rust irrelevant to North Dakota and other
states in the Midwest.

Sam Markell
Extension Plant Pathologist
samuel.markell@ndsu.edu

 

NDSU DISEASE FORECASTING WEB SITES

NDSUís crop disease forecasting web sites have a new portal this year. Links to small grain disease forecasting, Sclerotinia disease forecasting, and potato disease forecasting are available at one web address:

http://www.ndsu.edu/diseaseforecast

A person seeking information specifically on wheat disease risk, including fungal leaf diseases and Fusarium head blight (scab) may go directly to the following web address:

http://www.ndsu.edu/scabforecast

Scab forecast website
Opening page of http://www.ndsu.edu/scabforecast

This scabforecast web site has been reformatted for easier use. It provides information on the risk of Fusarium head blight (scab), as well as risk of the wheat leaf diseases, tan spot, Septoria blotch, and leaf rust. The risk of these four diseases is based on environmental conditions as recorded by the North Dakota Agricultural Weather Network (NDAWN) stations. This network consists of 67 stations distributed across North Dakota, the Red River Valley, and border regions of surrounding states.

The information in the models for the leaf diseases was developed at ND, and provides information in a chart format indicating risk of the three leaf diseases over the past 12 days. Such information is another tool that producers may use to determine the need for fungicide application at critical growth stages to control leaf and head diseases in wheat. The following graph was taken from the model in June 2005, as an example:

Disease risk at Mott

6/14

6/13

6/12

6/11

6/10

6/9

6/8

6/7

6/6

6/5

6/4

Tan spot

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

S. Blotch

No

No

No

No

Yes

No

Yes

Yes

No

No

No

Leaf rust

No

Yes

No

No

No

No

No

No

No

No

No

Example of leaf disease risk predictions, from June 2005

The risk map for Fusarium head blight is based on a model developed by plant pathologists at Penn State University, a model which incorporated considerable ND disease and weather data for verification of the model. The scab model also provides the opportunity for the producer to look at risk based on the susceptibility of the cultivar to Fusarium head blight.

Fusarium head blight risk
Example of map of Fusarium head blight risk, 2004

At the NDSU web forecasting site, a click on the flowering growth stage provides risk information in a chart format and state map format for Fusarium head blight.

A 1-888 toll free telephone service also will be activated for the current regional disease forecast information on May 30.

Direct access to the Penn State scab forecast site, which tracks risk in multiple states, may be found at:

http://www.wheatscab.psu.edu/

Scab forecasting site

 

UPDATE FROM SOUTHERN PLAINS STATES

Wheat leaf rust was found in Nebraska in counties adjacent to Kansas, as of May 14th. Oklahoma wheat has rapidly matured with recent hot temperatures in that region. The newest Cereal Rust Bulletin, with more recent rust observations, had not yet been posted, as of May 21.

Marcia McMullen
Extension Plant Pathologist
marcia.mcmullen@ndsu.edu


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