During the 2011 growing season, extension soybean pathologists from the north central states conducted a seedling disease survey to identify disease pathogens that cause damping-off in soybeans. The survey is part of a larger project that is being funded by USDA, explains Alison Robertson, Iowa State University Extension plant pathologist.
She provides the following information, explaining what was learned from last year's survey results and what is planned for this year's survey.
In the first year of this study, 54 Pythium species and two Phytophthora species, including Phytophthora sojae, were recovered from damped-off soybean seedlings collected from throughout the north central region. In Iowa, 19 Pythium species and Phytophthora sojae were recovered. Many of the species recovered have been reported as pathogens of soybean seedlings, but some of the species have not.
To determine if these other species are pathogenic on soybeans, "we will have to do what is called Koch's postulates," she explains. "This is the accepted scientific method for identifying the causal agent of a disease." Further research will include comparing the pathogenicity and aggressiveness among and within species, and assessing the sensitivity of each species to fungicides used in seed treatments, she says.
In 2012 this survey will continue, with additional funding from the United Soybean Board used to identify fungal pathogens (Fusarium spp. and Rhizoctonia species); pathogens associated with damping off of soybean. "Data from these studies will add to our knowledge of soybean seedling disease and lead to enhanced management through improved use of seed treatment fungicides and use of resistance," says Robertson.
Need to locate soybean fields that have "damping off" disease symptoms
This growing season, "I am again looking for soybean fields that have damping-off," says Robertson. "I need to collect 50 diseased seedlings from the field and bring them back to the lab for processing. If you know of a field with damping-off, please email me at [email protected] or call me at 515-294-6708, so that we can coordinate sampling of the field."