Timely planting is recognized as an important factor in achieving maximum soybean yields. Research shows, for most South Dakota farmers, May 15 is the target date for getting seeds in the ground. Early planting may maximize the amount of sun plants capture during the growing season, but it also can put soybeans at risk if soil conditions aren’t ideal.
Soilborne diseases and insect pressures can be more prevalent under cool, wet conditions. Farmers often use seed treatments containing fungicides and insecticides as seed insurance, sometimes without knowing if those treatments are truly effective. South Dakota State University (SDSU) researchers evaluated the effect of a fungicide and a combination of fungicide plus insecticide seed treatments on soybean production in three regions of the state. Studies took place in 2016 and were replicated in 2017.
Researchers observed, for both 2016 and 2017, insecticide seed treatments improved yields only at the Southeast Research Farm near Beresford. Scientists believe those yield improvements were due to seed treatments reducing feeding by early-season grasshopper populations and the overwintering generation of bean leaf beetles.
SDSU Extension Specialist and Field Crop Entomologist Adam Varenhorst says the results from 2016 and 2017 indicate that planting date had a significant impact on yields for all the research locations.
Overall, seeding rates and seed treatments had variable responses on yields. Because of the challenging growing conditions of 2017, greater yields were observed for later-planted soybean at two of the four locations.
“We didn’t see a lot of response in 2016, but most of the state had very good growing conditions so it was a low-stress planting environment,” Varenhorst says. “In 2017, the early season was very different. A lot of fields were planted early, but then they sat in the ground due to cool and wet conditions. Numerically, we observed a trend that seed treatments improved yields for early-planted soybeans in 2017.”
Varenhorst says farmers deciding if insecticide treatments are necessary should consider if early populations of bean leaf beetles and grasshoppers will be an issue in 2018. He says the later fall frost in 2017 likely meant grasshopper populations had a chance to grow. Ground cover availability and insect mortality due to cold temperatures are factors farmers should consider when determining if fungicide and insecticide treatments are needed. SDSU publishes a map in late winter showing likely insect mortality based on winter temperatures.
“Farmers will need to decide if the additional $9-$17 per acre for seed treatments is worth it for them,” Varenhorst says.
Varenhorst says 2017 research project data will be published on the iGrow website. SDSU Extension is also constructing a seed treatment calculator, and it will be available through iGrow. The calculator will help South Dakota farmers make decisions regarding the need for seed treatments on their farms.
Further research into the effectiveness of seed treatments is scheduled for the 2018 growing season.
To read more from the March/April South Dakota Soybean Leader, click here.
This blog post is brought to you by the South Dakota Soybean Research & Promotion Council.