Research HighlightsFoliar Fungicide Influence on Soybean Seed Quality in Early Planted Systems
In this article, you’ll find details on:
- Clemson University research found that foliar fungicides don’t improve soybean seed quality in indeterminate Maturity Group 4 soybeans planted early in South Carolina.
- Seed quality challenges can be linked to choosing varieties not bred and screened for the environment.
- In irrigated fields, the potential for higher yields may outweigh the seed quality risks of the early planted system. Timely desiccation and harvest, rather than foliar fungicides, may help mitigate those quality risks.
By Laura Temple
Soybean farmers try many different practices with the goal of improving yields. They weigh the risks and rewards of those changes, and they lean on unbiased research to mitigate risks.
“Interest in high-yielding soybean systems has led some soybean farmers in South Carolina to plant indeterminate Maturity Group 4 soybeans in April and harvest them in September,” explains Michael Plumblee, extension corn and soybean specialist and assistant professor of agronomy at Clemson University. “This system can boost yield, but they are seeing an uptick in seed quality issues at harvest, as some pods are more mature than others.”
These early soybeans often don’t dry down well, and soybean seeds appear discolored or wrinkled. Purple seed stain affects more harvested soybeans in this system, as well.
Farmers exploring this system wanted to know if foliar fungicides could improve or protect seed quality. They turned to Plumblee and John Mueller, professor of plant pathology at Clemson University, for answers. The South Carolina Soybean Board funded their research in 2023 to test the value of fungicide applications for addressing these seed quality issues, including optimal growth stage for application, the results with multiple applications and the potential financial return.
To test the efficacy of foliar fungicides, Plumblee and Mueller’s team planted plots of MG 4 soybeans in late April. Treatments included applying fungicides at three different timings during reproductive growth stages: R1, R3 and R5. Plots compared single applications with multiple applications at those timings.
The team desiccated plots in early September, prior to harvest. In addition to comparing yield, they pulled subsamples of harvested soybeans from each treatment, counted 100 seeds and visually estimated quality. They rated samples from each treatment for color, purple seed stain and wrinkled or shrunken seeds.
“Regardless of the treatment, we saw no difference in seed quality or yield,” Plumblee reports. “Statistically, all the treatments were the same as the untreated checks.”
He notes they experienced good weather during harvest and the absence of heavy disease pressure.
“In these trials, we saw damage rates of 10 to 19% across all the treatments,” he adds. “At the same time, we didn’t see much of a yield bump, and what we did see could be attributed mostly to early planting.”
Variety Fit Factors More Heavily than Fungicides
Mueller attributes the lack of response to a variety of factors that foliar fungicides can’t address.
“Shriveled seed is not a disease issue,” he says. “Fungicides control pod and stem blights, molds and other disease issues. Asian soybean rust is the biggest trigger for applying fungicide, and it doesn’t come every year. Target spot can also be a problem.”
In the absence of disease pressure, he looks at other aspects of the early planting system to explain seed quality challenges.
“MG 4 soybeans are not bred and screened in South Carolina,” Mueller explains. “They are not tested against the disease complex and conditions we have here.”
For example, MG 4 soybeans don’t carry resistance to Southern root-knot nematode, a common problem in South Carolina.
“Indeterminate MG 4 soybeans don’t appear to weather as well as determinate soybeans, either,” Mueller adds. That means they are more prone to damage to mature seed while waiting to be harvested.
“Given conditions in South Carolina, farmers are usually better off protecting moderate soybean yields, rather than chasing higher yields like farmers in other regions can do,” he says.
Mueller and Plumblee encourage farmers to carefully consider the fit of the early planted system for their operation. Traditionally, South Carolina farmers plant MG 5 through MG 7 soybeans in May or June for harvest in late October. They say these soybeans average about 40 bushels per acre in dryland systems. The early planting system with MG 4 soybeans moves everything up about a month.
Another Clemson trial compared the yield of MG 4, 5, 6 and 7 soybeans planted every month from April through August. In dryland fields, they learned that maturity group selection did not impact yield as much as historically thought when coupled with varying planting dates. Thus, selecting a well-adapted variety planted late-April through mid-May provided some of the highest yields.
“However, under irrigation, MG 4 soybeans can yield an average of 55 bushels per acre,” Mueller says. “In irrigated fields, there is some opportunity to get better yields, but growers need to be aware that seed quality is still a risk.”
Plumblee adds, “Farmers opting to plant MG 4 soybeans early need awareness that the fields need to be desiccated and harvested on time. They can’t spray their way out of this type of seed damage.”
With that in mind, Plumblee has turned his focus to desiccation timing as a way to preserve soybean seed quality. He is leading South Carolina’s participation in a multi-state Science for Success trial.
Additional Resources
- Can Aggressive Pest Management Protect Seed Quality? – SRIN article
- Weathering Well: Variety Screening to Protect Harvest Quality – SRIN article
- Scouting for Common Soybean Seed Diseases – Crop Protection Network
- Exploring Desiccant Usage for Better On-Farm Decision Making – SRIN article
Published: Nov 4, 2024
The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.
