You may not normally scout soybeans in late September. Getting ready to harvest them at this time of year is a more normal activity — but it’s not a normal year. If you have late-planted soybeans, Steve Gauck suggests scouting them now so you can identify diseases and possible insect issues. There’s nothing you can do about diseases for this crop, but it could help you make decisions for 2020. There may still be time to protect the crop from significant late-season insect damage if you find treatment is warranted.
“I’m just now beginning to see signs of SDS in some fields, even though it’s the third week of September,” says Gauck, a Beck’s sales agronomist based near Greensburg, Ind. “First symptoms include yellow, interveinal chlorosis and necrosis, or dying, of leaf tissue.”
Here’s the question Gauck gets most often when sudden death syndrome begins to appear. Will it infect the rest of the plants in the field?
“You have to understand how this disease works,” Gauck says. “No, SDS won’t spread from an infected plant to plants nearby. It’s a rot, and deterioration occurs within the plant. It doesn’t move from plant to plant.
“However, once you see an infected plant, you may see other plants nearby show signs of infection over the next few days or weeks. But the infection in those plants happened much earlier, during the vegetative stages.”
Why this year?
You normally wouldn’t expect serious SDS problems when most soybeans were planted in June. If 2019 is anything, it’s not normal, Gauck emphasizes. Many soybeans were planted during the first two weeks of June. Then it turned cool and wet for up to 10 days in many areas. Temperatures plummeted into the 40s at night, while soils were saturated.
These were the same conditions that caused chilling injury on corn planted June 14 and prevented germination, Gauck says. That’s not normal either. So just because the calendar said June 15 certainly doesn’t mean SDS couldn’t infect plants, he adds.
According to the Purdue University Corn and Soybean Field Guide, wet conditions when soybeans flower followed by dry conditions later tends to encourage expression of SDS symptoms in infected plants. That describes the recent weather pattern in many areas.
“If you see leaf symptoms and split a stem open, and it’s white inside, it’s likely SDS,” Gauck says. “Brown stem rot would turn stem tissue dark. If it’s SDS, you can sometimes see small water marks along the inside edge of stem tissue.”
Other diseases, insects
Scouting in a field treated with Ilevo seed treatment, Gauck found an isolated plant or two showing symptoms of SDS. The Ilevo seed treatment protects against SDS infection. “It’s not bulletproof,” Gauck says. “You may still see a few plants which are affected if the disease is present.
“We’re seeing some yellowing of leaves, especially lower leaves, in fields this week, which might make you suspect SDS, but the symptoms don’t quite match up. If it’s a disease, it may be a bacterial disease. Some leaves deep in a dense canopy turn yellow because they’re not getting sunlight.”
Leaves naturally begin to turn yellow as plants mature, although it seemed too early for that in some late-planted fields Gauck walked this week.
“We’re also beginning to see some stinkbugs and stinkbug nymphs,” he adds. “Since they can jump to the pods once leaves do dry up, I would keep scouting for them. It’s too early to rule out a late insecticide application to protect pods if stinkbug numbers warrant it.”