A new late blight strain type, US-25, has been identified in New York State. To date, this new strain has only been found on tomato. Christine Smart, a professor at Cornell University, has been keeping potato pathologists informed on US-25, which is now known to be Ridomil/mefenoxam-resistant, says Eugenia Banks, a potato specialist with the Ontario Potato Board.
US-25 is of the A2 mating type, and under laboratory conditions will infect potato as well as tomato, says Banks.
The current predominant strain in Canada and the United States is US-23, which is of the A1 mating type and is susceptible to Ridomil.
