Suppose yellow spots appeared on upper soybean leaves before the leaves should have been turning yellow last summer. Your seed dealer diagnosed it as sudden death syndrome. Fortunately, it wasn’t widespread, so it may not have trimmed yields severely. Odds are, though, there was some yield loss.
“Although you didn’t see symptoms until late summer, the infection started much earlier,” says Steve Gauck, a Beck’s sales agronomist based near Greenburg, Ind. “In fact, infection likely occurred early in the season, between germination and emergence.”
This is the third season in which Gauck will scout a soybean field in east-central Indiana, looking for symptoms like those caused by SDS. It’s the Soybean Watch project. The goal is to uncover trends and problems in one field that might also be important for you to monitor in your fields. Beck’s, Atlanta, Ind., sponsors Soybean Watch ’19.
What and where
SDS limits root growth, Gauck says. Eventually, roots deteriorate, and bacteria nodules break down. When the disease advances far enough, you’ll see yellow spots on upper leaves, usually in late July or August.
“Disease severity is very dependent on weather conditions, time of infection and overall stress on soybean plants,” Gauck says. “That’s why timing and severity of disease outbreaks vary from year to year.
“Leaves drop prematurely. Petioles stay attached to the stem.”
CLASSIC SYMPTOMS: Here are plants and leaves showing signs of SDS infection. This disease can rob yield from soybean fields.
By the time you see symptoms, it’s too late to do anything about SDS that year, Gauck says. However, careful scouting will help you identify hot spots and prepare for the next time the field goes to soybeans.
A soilborne fungus that overwinters in residue causes the disease, Gauck notes. Soybeans are most vulnerable when planted early in cool, moist conditions. Fields with a history of SDS or ones known to have heavy soybean cyst nematode pressure are the most likely candidates.
“High-yielding fields are also more prone to SDS since more stress is applied to reach high yield,” Gauck adds.
Poorly drained areas within a field that isn’t tiled or areas that are compacted are also prime candidates for SDS. That’s why it sometimes shows up in end rows where the planter overlaps.
If you know you have SDS or find it this year during scouting, look for genetics with good tolerance to SDS for 2020, Gauck advises. Improving drainage through tiling and minimizing soil compaction throughout the season are also positive steps.
The seed treatment Ilevo suppresses SDS by protecting against the fungus that causes it. It also controls nematodes in the seed zone. “By protecting the plant early, we stop infection of roots and keep the root system healthy,” Gauck says.
Even most seed companies that routinely treat soybeans don’t add Ilevo unless requested. It can cost up to $10 per unit to apply. Still, Gauck reports that in Beck’s Practical Farm Research testing, adding Ilevo averaged an $11.59-per-acre return on investment over the past four years.