Seedling diseases and seed rot accounted for more than 20% of soybean establishment problems in the past five years, and farmers had to replant almost 20% of affected acres. (This comes from a March 2012 survey of Midwestern and Southeastern certified crop advisors in 12 major soybean-producing states as part of a soybean seedling disease study.)
From 2005 to 2007, the seedling disease yield cost is estimated at 37 million bushels/year, yet “many states don’t know a great deal about what causes seedling diseases in their area,” says Martin Chilvers, a Michigan State field crop pathologist.
Chilvers’ lab, together with university collaborators from 12 major producing states, is examining soybean seedling diseases to identify the range of soybean pathogens. Testing in the laboratory and greenhouse will follow to determine which ones cause disease and rule out organisms that are only “guilty by association.”
Identifying what’s actually causing disease, will lead to better seed treatments or genetic solutions, he notes.
“We might need to tailor seed treatments to different growing regions. So far, species tend to group by similar geography,” says Chilvers of the 55 species of Pythium and two species of Phytophthora identified in 2011 and the 40 species of Pythium and two Phytophthora from 2012.
“We noticed a big shift in species composition from 2011 to 2012 that is very likely associated with weather. Certain soil components also seem to drive what’s there. Temperature, soil texture and precipitation seem to be linked to this,” he explains.
“We’ve opened a can of worms,” says Alison Robertson, Iowa State University plant pathologist, speaking at a January Crop Advantage workshop in Ames. “We’re finding a range of species that will cause disease, and not all will respond to fungicide seed treatments.”