Pythium on seedlings. Photo by Ohio State University Extension.

Pythium problems showing up in Ohio

It is an unsettling sight no soybean grower wants to see — entire fields dying shortly after emergence. This, though, is an unfortunate reality in some fields around Ohio.

On May 14, Asgrow Dekalb agronomist Jeff Rectenwald was scouting fields for a customer in Auglaize County when he came across the aftermath of Pythium seedling blight.

“I ran across entire soybean fields dying from seedling blight as they were emerging from the soil surface,” Rectenwald said. “You can see the fungal lesion at the top of the hypocotyl’s arch as the soybeans were breaking the soil surface.”

You can see the fungal lesion at the top of the hypocotyls arch as the soybeans were breaking the soil surface. (Photo by Jeff Rectenwald).

The soybeans were planted on May 2 and will be replanted, Rectenwald said. Regular scouting around emergence is important in quickly identifying the problem.

Unfortunately, the rain and persistently cool soil temperatures this spring are optimum conditions for a large and diverse group of pathogens called water molds, according to Anne Dorrance, Ohio State University Extension plant pathologist. The cool soil slows plant growth and opens up a wider window for Pythium to do its damage.

Plant pathologists have identified more than 25 different species of Pythium in Ohio fields that can infect both corn and soybean in Ohio’s production fields.

“These are the fields that require replanting. You know, you put the right amount of seed in the planter, but the rows look thin and the yields are off by 10 to 15 bushels,” Dorrance said in the CORN Newsletter. “When seed is planted into these cool soils, and more rains come (this is Ohio after all), the ground becomes saturated for a short time. These are perfect conditions for these water molds to develop the swimming spores, called zoospores. What is very unique about this group of organisms is that these zoospores are attracted to seeds and seedlings through a process called chemotaxis.”

The challenge is that, with so many types of Pythium, seed treatments can control some of what is in the field, but most likely not all.

“Still use the seed treatment, but more importantly, plant in the most optimum conditions for the seed to germinate quickly and get established,” Dorrance said. “This is especially important for those fields that have poor drainage.”

(Photo by Jeff Rectenwald)

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