Soybean rust found in Iowa

Encyclopedia Article

On Tuesday, March 13, 2007, Iowa State University, the Iowa Department of Agriculture and Land Stewardship, and the Iowa Soybean Association jointly announced for the first time that soybean rust was found on plant tissue reported to be from Iowa.

Here is what we know so far:

  • A sample of soybean seed, pods, and a single leaf was taken from a bin in Iowa containing soybeans that were reported from an unthrifty field last fall. The soybeans were of maturity group 3.7 in a field planted in late May.
  • This sample was brought to the Iowa State University Plant Disease Clinic on March 8, and pustules and spores consistent with Asian soybean rust were found on the leaf.
  • On Thursday, March 8, a sub-sample was sent to the USDA labs in Beltsville, Maryland, for confirmation.
  • On Monday, March 12, USDA scientists in Beltsville confirmed by molecular analysis that the sample contained soybean rust.
  • Efforts are underway to identify other remnant plant residue from the affected field and seed bins that may show symptoms and signs of the disease in order to clarify details of this event.

What are the ramifications for 2007?

The confirmation of soybean rust in the 2006 crop does not guarantee that we will have soybean rust in the 2007 Iowa soybean crop. The spores that cause soybean rust cannot survive without green leaf tissue and will die during Iowa winters, so the recently discovered rust fungus does not pose any risk of infection for the 2007 Iowa growing season.

However, this discovery does remind us that it is possible for Iowa fields to become infected with soybean rust. Growers should not overreact to this development. Instead, growers must be ready to act appropriately and economically in 2007 should this disease again show up in Iowa and be a threat to soybean yields.

Spores from the Iowa Asian soybean rust sample viewed under a microscope. (Christine Engelbrecht)

Magnified pustules from the Iowa Asian soybean rust sample. (Christine Engelbrecht)

This article originally appeared on page 56 of the IC-498 (3) -- March 26, 2007 issue.

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