Late-planted soybeans may be at risk for potential yield loss from soybean rust and other diseases, said a Purdue Extension crop disease specialist.
Soybean rust usually arrives in Indiana when soybeans are mature or nearing maturity, so there is lower potential for yield loss. But there could be yield loss if soybean rust reaches Indiana while they are still in the early stages of reproductive growth, said Kiersten Wise. With about 45 percent of Indiana soybeans planted after May 30, some of the crop could be at risk.
But because of weather conditions in the southern part of the country, where soybean rust overwinters, late planting in Indiana doesn't necessarily lead to a higher risk of soybean rust later in the season, Wise said.
"Right now, the South is experiencing moderate to extreme drought conditions," she said. Soybean rust needs adequate moisture to develop, and the drought conditions in the South have slowed soybean rust development and spread in 2011."
Soybean rust is transferred in the spring from kudzu, an invasive weed, to soybeans. The spores can then be spread long distances by hurricanes and storms that move the disease northward.
"If soybean rust is not managed properly, it can be very damaging," Wise said. "In Indiana, we have taken measures to detect the disease early and prevent yield loss. Scientists monitor its development and spread in the South and we can issue fungicide spray advisories if rust looks like it will become a problem in Indiana."
In addition to soybean rust, other diseases can potentially reduce yields in late-planted soybeans. One disease, Phytophthora root rot, a type of seedling blight, is common with heavy rains, and saturated and warm soils.
"Farmers need to check areas of fields with poor seedling emergence and poor stand development," she said. "Seedling blights, like Phytophthora root rot, can cause yield loss, but unfortunately there are no in-season management practices for these diseases."
If growers find root rot, they should note the fields affected, and they should use effective seed treatments and disease-resistant varieties the next time soybeans are planted there, Wise said.
More information about soybean rust development can be found at http://sbrusa.net/.
Growers also can call the toll-free hotline at 866-458-RUST or subscribe to the Indiana soybean disease email list at https://lists.purdue.edu/mailman/listinfo/indiana-soybean-update/