Weather Extremes Are Learning Opportunities
How well the crops are protected by seed treatments and resistant varieties, where applicable, may be telling. For example, there are many different races of phytophthora in Minnesota that render the common resistance genes in soybean ineffective in some fields. Malvick also reported that some seed treatments appeared to miss their target.
“Pythium is generally controlled by the seed treatments targeted at a few previously identified species,” he said. “But pythium seemed to overcome the seed treatments in some areas.”
What is yet unknown is whether it was the environmental conditions or the species that may not be very sensitive to the seed treatments. Malvick reported finding more than 20 different pythium species while sampling soybean fields. He admitted that much is unknown about them.
“We don’t know about their relative aggressiveness or pathogenicity, when they thrive or under what conditions,” he said. “Pythium is generally considered to thrive in cool and wet conditions; however, some of these species may prefer warmer soils.
He cited the loss of several thousand acres of corn in south central Minnesota in 2012 as likely being caused by pythium root rot. Although drenching rains caused crusting, it appeared to be the root rot that killed the seed-treated corn.
“Based on work in other states, it appears pythium species are not all equally susceptible to seed-treatment fungicides,” said Malvick. “We need to understand what these different species are doing in Minnesota.”
More information is needed on fusarium as well. Malvick noted that while it has long been known to be a problem in soybeans and corn, no highly effective treatments have yet been found. Although soybean varieties have been developed with resistance to the fusarium species causing SDS, that is not the case with other species. His concern is that the problem is more complicated than previously thought and may be getting worse.
“We have found 12 different fusarium species while looking at root rot in corn and soybeans,” said Malvick. “The issue is whether we look at enough fields under the same conditions to really know if things are changing. It is difficult to get enough information, but fusarium appears to be thriving and possibly changing to be a little more effective on corn and soybeans. That may be the case with pythium as well.”
Malvick pointed to new tools on the horizon, including new seed treatment fungicides and biological seed treatments, some of which are already included in seed treatments. The wet conditions in the upper Midwest and resulting disease pressure are providing ample challenges to current control methodologies. These new controls may well prove extremely valuable.