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Issue No. 24, Article 7/November 5, 2004

Asian Soybean Rust Confirmation in Lousiana Raises Concern of Potential Impact of this Disease in Illinois

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As widely reported on Nov, 10, 2004, Asian soybean rust was confirmed this week for the first time in the continental U.S. Soybean rust is a fungal disease of soybeans that infects leaves and can cause defoliation and significant yield losses. The soybean rust reported in Louisiana was Asian soybean rust, the aggressive species of rust (Phakopspora pachyrhizi), not the relatively mild American soybean rust (P. meibomiae).

As has been said many times: "it's not if soybean rust will arrive in the continental U.S, it is when" Now we know when for the Continental U.S., but we still do not know when it will arrive in Illinois--it may be in 2005 or not for another few years. Nor do we know how much damage it can or will cause in Illinois. The yield losses in Illinois may be significant but also may be much less significant than some have suggested. There are many questions that will not be answered before this disease arrives in Illinois. Regardless, the risk of soybean rust occurring in Illinois in 2005 has now increased substantially with the discovery in Louisiana.

A few key things to note:

  • The Illinois Department of Agriculture, along with a team of representatives from several federal and state agencies, and the University of Illinois Extension has developed a plan of action (Illinois Soybean Rust Program) to diagnose and manage Asian soybean rust if it arrives in Illinois. This plan can be found on their web site.
  • Soybean rust is not expected to survive over the winter in Illinois or adjoining states. Spores of this pathogen must be blown up from infected plants in the far south to initiate infections in the Illinois soybean crop. Some models suggest the overwintering sites of soybean rust may be restricted to the gulf coasts of Florida and southern of Texas, or in Mexico.
  • The climate over much of Illinois will not always be favorable for widespread and severe soybean rust epidemics.
  • Management of soybean rust will be dependent in the next few years on judicious use of fungicides. The appropriate fungicides applied properly at the correct time have been shown to control rust in other countries. Applications at the earliest time possible after rust is detected will be most effective. At least 6 to 10 different fungicides should be available for soybean rust management if they are needed in Illinois for the 2005 crop.
  • Highly resistant soybean varieties will probably not be available for a number of years, however, there may be varieties available sooner that have tolerance or partial resistance to soybean rust.
  • Much more information on soybean rust will be presented at conferences and workshops organized by the University of Illinois Extension this coming winter. One to keep in mind is the Illinois Crop Protection Technology conference where sessions will cover soybean rust in depth. Soybean rust will also be covered at the Southern Illinois Crop Management Conference in Effingham on Feb. 8-9, the Central Illinois Crop Management Conference in Jacksonville on Feb 22-23, and Northern Illinois Crop Management Conference in Malta on March 1-2, 2005. Contact your local U. of Illinois Extension office to learn of more about educational programs that will cover soybean rust in your area.

What are the risks of soybean rust arriving in Illinois in 2005 and causing considerable damage in Illinois? There is no way we can know for sure, there are too many environmental, biological and other factors involved to predict this with any degree of certainty. The following report provides a useful outlook on the risks of soybean rust arriving in the upper Midwest and how much damage it may cause. This report was developed by the USDA-Economic Research Service on the Economic and Policy Implications of Wind-Borne Entry of Asian Soybean Rust into the United States. "This report examines how the economic impacts of soybean rust establishment will depend on the timing, location, spread, and severity of rust infestation and on how soybean and other crop producers, livestock producers, and consumers of agricultural commodities respond to this new pathogen." The risks appear to be different in different parts of Illinois and will not be the same every year.

Dr. X.B. Yang from Iowa State University suggests that the incidence and severity of soybean rust in the spring in the southern U.S may be an indicator of whether this disease will become a problem in Illinois or Iowa later in the season. Two factors to consider are that to our knowledge, there have been no widespread and severe plant disease epidemics in their first year of detection after introduction into the U.S, and that its likely that before an epidemic will occur in Illinois it will take time for the rust pathogen to increase its population in the south to a sufficient amount in order to be spread to north.--Dean Malvick

Useful web sites for more information on soybean rust.

USDA Soybean Rust Web site

Plant Heath Initive site

Soybean Rust: Is the US Soybean Crop At Risk?

Soybean Rust Backgrounder from the American Soybean Association

Information compiled by the UIUC Department of Crop Sciences

Dean Malvick

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