Fall 2018's cool, damp weather has put the brakes on many acres of soybean harvest this year.
"This year has been the perfect storm of late season moisture and temperature to cause harvest and seed quality issues," said Sara Bauder, SDSU Extension Agronomy Field Specialist. "We cannot always avoid these problems, but salvaging the best harvest possible and managing for next year should be first priority."
To aid South Dakota soybean growers, Bauder, together with Laura Edwards, SDSU Extension State Climatologist and Connie Strunk, SDSU Extension Plant Pathology Field Specialist, share best practices.
"Although South Dakota has seen late harvest seasons in the past, this year is testing many farmers' patience considering the wet weather of the past few weeks and current climate outlook," Edwards explained.
Edwards references data from the High Plains Regional Climate Center, explaining that October started out very wet, following on the heels of an exceptionally wet September.
"In the Sioux Falls' area, 9.5-inches of rain was reported between September 1 and October 9," Edwards said. "This excessive moisture has made field access impossible and stalled grain drying in field."
Edwards added, "Cool temperatures have further limited evaporation and the ability to dry grain in the field."
Drier weather predicted
Although current forecast models predict drier weather ahead, (as of October 10, 2018), with cool temperatures gradually moving east, Edwards said even if predictions are true, they will not help South Dakota's soybean growers much.
"There is limited ability to warm up substantially at the end of October, as days are shorter and we have lower sun angle than in mid-summer," Edwards said. "The additional moisture in the soils and atmosphere also limits warming and grain drying after the rain ends."
Bauder said for most, the best case scenario this soybean harvest is to wait out the weather.
"This means, waiting until the precipitation stops and the sun comes out, making soils dry enough for field traffic-ability and hopefully lowering seed moisture content," she said.
Based on multiple factors, many producers have made the decision to store soybeans on-farm. Some of these factors include:
• Farmers holding over old grain
• Many commercial outlets only accepting dry soybeans (less than 13 to 14 percent moisture)
• Increased commercial storage costs in some areas
• Current market outlook
"For long-term storage of soybeans (several months up to a year), it is recommended to dry soybeans down to 11 percent moisture," Bauder said. "With drying facilities available on-farm, some producers may choose to harvest wet beans, but others will most likely wait out the damp fall as long as reasonably possible."
Cool & humid conditions not ideal
"Under these cool and humid conditions, seeds will tend to absorb additional moisture from the atmosphere, which will most likely cause many fields to be harvested above 13 percent this year if dry weather is not predicted soon," Bauder said.
As soybean pods mature and turn brown, seed moisture begins to decrease quickly.
In a three-year Iowa State University study, researchers found that soybeans' dry down weight was affected by maturity group selection, planting date, and year.
The study found in the first 12 days after plant maturity begins, soybeans dried rapidly at 3.2 percent per day. Then, after 12 days, dry down was stabilized at approximately 13 percent moisture (Figure 1).
Grain quality issues
Depending upon how long crops may need to remain in the field, grain quality may become a concern, because certain diseases thrive in current weather conditions,explained Strunk.
"Many fungal soybean diseases, such as Diaporthe pod and stem blight, Frogeye leaf spot, Anthracnose and many other secondary fungi, can impact seed quality," Strunk said.
Strunk said that at this point in the season, soybean growers' main concerns are moisture and storage temperatures to prevent spoilage during storage.
"The best way to protect your crop from seed quality problems is to get it out of the field and dried down as soon as possible," Strunk said. "However, when balancing the forecast and drying costs with potential quality issues, each producer needs to consider what is best for their operation."
Consult nutritionist before feeding infected soybeans
If soybeans are heavily affected by a late season fungi, they may reflect poor seed quality. And, Strunk said that although these soybean fungi are not known for toxicity, a livestock nutritionist should be consulted before adding any soybeans to a feeding ration.
When storing infected grain, Strunk said keeping it dry is key to preventing further colonization and maintain the best seed quality possible.
"We can avoid re-occurrence of some of these late season diseases by implementing crop rotation, planting resistant lines in 2019, utilize a fungicide seed treatment and regularly scouting for disease infestation on stems and pods," Strunk said.