Continuing survey work for soybean seedling root rots again found Phytophthora sansomeana along with the endemic Phytophthora sojae. P. sansomeana was first detected in Wisconsin in 2012; results from the 2013 survey of 50 randomly-selected soybean fields and two corn fields showed soybean roots from four soybean fields and corn roots from one corn field were infected. Survey staff re-sampled the three fields in 2013 that tested positive for P. sansomeana in 2012, including two fields that had been rotated to corn. Fields were sampled between June 17 and July 18. While the significance of this P. sansomeana find is being investigated, it is the host range that raises concern about this organism. With both corn and soybeans being susceptible to infection (though the development of disease on corn has not been documented in Wisconsin to date), the potential for increases in inoculum is significant, given the widespread use of corn/soybean rotations.
Soil Science Extension
University of Wisconsin Madison