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Soybean Phytophthora Root Rot Survey

Dale Baird, Extension Educator – Crop Systems, Rockford Extension Center, 815-397-7714, bairdd@uiuc.edu

Soybean Phytophthora Root Rot (PRR) disease has become more common throughout the Midwest during the past five years. PRR is caused by a soilborne pathogen that has been kept in check in the past with PRR resistant or tolerant varieties. PRR resistant soybean varieties contain resistant genes or Rps genes that trigger the production of an antifungal compound in soybeans. Forty-five different races or strains of PRR have been identified, but not all races have been confirmed in Illinois. The Rps1-k gene controls several common PRR races and is the most widely used Rps resistance gene in commercial varieties. However, the Rps1-k gene is not effective against several of the "new" PRR races confirmed in the Midwest during the 1990s.

Dr. Dean Malvick, University of Illinois Extension plant pathologist has initiated a PRR Survey. The survey objective is to isolate and identify possibly new PRR races in Illinois. If you suspect you have PRR in 2002 or have a field that has a history of PRR infection contact your local Extension office. A Crops or IPM Educator will collect soil and plant samples and forward them to Dr. Malvick for potential race isolation.

Seedling stage PRR is characterized by a bruised, soft, brown root rot before emergence or shortly after emergence. PRR at the seedling stage can easily be confused with Pythium or Rhizoctonia. Rhizoctonia can be confirmed by observing a reddish lesion on the root. Later season PRR is characterized by yellow, wilting and dying soybean plants. On closer inspection usually a distinct dark brown discoloration can be observed on the plant stem that extends upward from the soil line.