Asian soybean rust has been confirmed for the first time in Kansas according to researchers from Kansas State University and the Kansas Department of Agriculture. The researchers say that a leaf sample from a soybean plant collected at a sentinel plot in Montgomery County tested positive for the disease. The site where the positive sample was found is one of 20 that the USDA planted to monitor for the disease.

 "There are 300,000 to 400,000 acres of late-planted soybeans this year that are potentially in danger,” says Kansas State University plant pathologist Doug Jardine.. This represents about 10 to 15 percent of the state’s crop."

"To scout for soybean rust, you should arbitrarily collect or observe a minimum of 100 leaflets from the lower canopy (older, main-stem terminal leaflets) in each field," Jardine said. To observe pustules, a minimum 20X hand lens is needed, but 30X is better. Pustules will be found on the bottom side of the leaflets and have the appearance of small volcanoes within the lesion."Any soybean field that has reached the R6 stage of development (full pod fill) is no longer in danger from the disease, Jardine said.

The decision to spray is dependent on a combination of growth stage, application costs, expected selling price and the yield that will be saved by spraying. Given the level of disease currently being found, yield savings would likely be no more than about 10 percent.

Kansas State Research and Extension has developed a calculator spreadsheet to assist producers in making the decision whether to spray. It is available on the AgManager Web page at www.agmanager.info.

Growers can access information about fungicides currently registered for use in Kansas from the Kansas Department of Agriculture Web site. For photos and further information on the disease´s symptoms, follow this link (PDF format).

Producers or scouts can submit samples of suspect soybean leaves for evaluation at Kansas State through any county or district Cooperative Extension Service office, Jardine said. He recommended:

  • Send 10-15 suspect leaves.
  • Place the leaves in a zipper-style plastic bag with a tight seal, and put that bag in a second such bag. Seal both bags securely.
  • Attach a note or write on the outer bag that this is a soybean rust sample.
  • Do not add wet paper towels or other types of moisture to the bag.
  • Try to mail it in the Monday-Wednesday time frame.

Source: Kansas State University