PAT MELGARES
K-State Extension news service
MANHATTAN, Kan. — Kansas farmers wrapping up harvest season are being urged to stay alert to crop diseases that could impact next year’s yields, according to Rodrigo Onofre, row crop plant pathologist with K-State Extension.
For soybean producers, the primary concern remains the soybean cyst nematode (SCN) — a microscopic pest responsible for the greatest yield losses in U.S. soybeans.
“The soybean cyst nematode is the number one yield-limiting pathogen of soybeans,” Onofre said. “In Kansas, we’re seeing high levels of SCN, especially in central Kansas.”
The nematode has now been identified in 64 Kansas counties, accounting for more than 85% of the state’s soybean production. Because it often causes no visible symptoms during the growing season, Onofre said it can silently rob producers of 2 to 10 bushels per acre.
“It’s a difficult pathogen to identify in the field,” he said. “Sometimes we don’t even see it during the year, but then the harvested crop is lower than usual.”
Onofre recommends testing fields for SCN soon after harvest when soil conditions are good for sampling. “It’s going to be easier for you to collect those samples and start planning for next year — either for a better variety, a rotation, or even a seed treatment, depending on your levels,” he said.
Samples can be sent to the K-State Plant Diagnostic Lab in Manhattan, or producers can contact their local extension agent for help submitting soil samples.
Corn growers, meanwhile, face increasing challenges from tar spot — a fungal disease that has expanded its reach across Kansas in recent years.
“Tar spot has been in Kansas for three or four seasons now,” Onofre said. “We’ve seen it move toward the western and central parts of the state. That worries me a little bit because those were late-season detections.”
The disease has been especially active in northeast Kansas, but recent reports in Lincoln and Smith counties mark its westward spread. Western Kansas’ reliance on irrigation, coupled with cooler fall temperatures, can create ideal conditions for the disease to thrive.
“Producers should still be scouting for tar spot, but consider adding a corn hybrid that is resistant to tar spot,” Onofre said. “Through resistance alone, we can see yield benefits of up to 10 bushels compared to susceptible hybrids.”
He advised producers to watch for black lesions that resemble insect droppings but don’t rub off the leaf surface. Crop rotation offers limited protection, he added, so hybrid selection remains the best long-term defense. In-season fungicides may also provide benefits.
This fall’s wetter-than-average weather has also increased the risk of corn ear rots, including Diplodia, Gibberella and Aspergillus.
“Moisture is a good thing, but it brings humidity and lower temperatures, which are ideal conditions for moldy ears and potential mycotoxins,” Onofre said.
Diplodia ear rot does not produce mycotoxins, but Gibberella does — posing risks to livestock if infected corn is fed as grain or silage.
For assistance in identifying diseases in corn or soybeans, growers can contact their local extension office or the K-State Plant Diagnostic Lab at 785-532-6176 or [email protected].