While there’s no silver bullet to control all soybean seedling diseases, there is one environmental factor farmers should pay close attention to each season.
“Seedling diseases are favored in wet conditions at planting, from emergence through the early vegetative stages,” Nathan Kleczewski, GROWMARK pathology/entomology technical specialist and past University of Illinois field crop pathologist, said during the ILSoyAdvisor Soybean Summit.
And with a plethora of disease threats each season, from Pythium to phytophthora, farmers should focus on an integrated pest management (IPM) approach to minimize potential disease outbreaks and the subsequent impacts.
Research shows at full seed, there is a 7% reduction in yield potential for every 10 unit increase in the disease index with sudden death syndrome (SDS).
“Research shows the best, most profitable and most effective way to minimize (seedling disease) issues is an integrated pest management approach,” Kleczewski said.
An IPM approach includes cultural practices, such as crop rotation and residue management; utilizing host resistance when available; and the use of seed treatments and biological controls, particularly in fields with a history of disease issues.
Seed treatments, which generally work for three to four weeks, are active in the root zone and help improve crop germination while boosting yield potential by about 3%. But they do not fumigate the soil or cure dead seed.
Farmers should also select varieties with resistance to diseases, including SDS. Resistant varieties provide about a 15% increase in yield potential in fields with a history of SDS.
And, oddly enough, researchers are finding SDS spore production is greater in a soy/corn/soy rotation, so farmers should focus on residue management in the soil following the corn crop.
Rhizoctonia, another seedling disease prevalent in Illinois, caused by a fungus, conversely is aggressive in corn but not as much in soybeans, so rotation helps control it.
But there are no cultivars resistant to rhizoctonia, so farmers should focus on practices such as reducing compaction, improving drainage and the use of seed treatments as other means to control the disease.
Those management practices also help control the 18 to 19 species of Pythium and two species of phytophthora present in Illinois.
With so many different seedling diseases, crop scouting is essential to assess any outbreaks.
“It’s important if you have seedling issues, send a sample to a diagnostics lab,” Kleczewski said. “You want to make sure it’s diagnosed correctly. There are different management recommendations.”
Lastly, the pathologist doesn’t see any greater risks for a disease outbreak based on planting date, as more farmers consider planting soybeans before May. The main factor to watch should be soil conditions and the weather pattern.
“There’s an old thinking that if we plant early, there’s a higher chance of SDS,” Kleczewski said. “A lot of times, there’s no significant difference. The correlation is not consistent (between planting date and disease probability) because we never know when it’s going to rain.”