Should you treat soybean seed this year?
It depends, says Jonathan Kleinjan, South Dakota State University Extension agronomist.
One factor is the weather. Cool temperatures and wet soils in early to mid-May will favor the development of soybean seedling and root diseases. Fungicide seed treatments can be effective at managing seedling blights and soybean root rots.
“Currently, there are no soybean varieties available to growers with genetic resistance to the pathogens that cause seedling and root diseases such as pythium root rot, fusarium root rot and rhizoctonia root and stem rot [damping off],” Kleinjan says. “While there are soybean varieties available with partial genetic resistance to phytophthora root rot and sudden death syndrome, fungicide seed treatments can provide additional protection against these pathogens.”
Insecticide seed treatments
Insecticide seed treatments target several above- and below-ground early-season insect pests. Below-ground insect pests include wireworms, seed corn maggots and white grubs. Early-season above-ground pests that insecticide seed treatments are labeled for include bean leaf beetle and grape colaspis beetle.
Some seed treatments are also labeled for soybean aphids, but insecticide seed treatments have a period of effectiveness that ranges from 20 to 40 days, depending on environmental conditions, and soybean aphids typically infest soybeans much later than this time frame, Kleinjan says.
What SDSU research says
Ongoing research at SDSU is examining the efficacy of both the fungicide and insecticide components of a seed treatment package to determine which is most important to protect soybean yields.
In 2015, a soybean seed treatment study examined five different types of seed treatment packages on a commonly planted soybean variety at two locations. The soil at the Brookings location was heavy and somewhat poorly drained, and the soil at the Volga location was well-drained and highly productive. The results from this study found from 1 ½-bushel to an 8-bushel-per-acre yield advantage over the untreated check. Anything over a 4-bushel yield difference was considered to be statistically significant.
In 2016, there was a 2- to 4-bushel advantage for treated seed, but it wasn’t statistically significant.
“It is important to remember that while yield response to seed treatment was evident, this level of response may not be evident every year in every growing location. In some years and at some locations, there may be no response to seed treatments. It is difficult to predict which seedling diseases and insect pests will be a problem from one year to the next,” Kleinjan says.
He recommends treating soybean seed if there is a concern about early-season disease or insect pressure — for example, if a field has a history of root rot or if a field has problems such as soil compaction or poorly drained soils.
Seed treatments can also help protect plant populations when using low seeding rates or planting seed with a less-than-ideal germination rate, Kleinjan says.