Telenko: Tar Spot May Cause Stalk Lodging at Harvest

Photos courtesy of Purdue University.

As Indiana’s farmers get set for harvest in the coming weeks, one concern may come from Tar Spot—which has now reached all corners of the state.

“For this season we do have new areas where Tar Spot is causing a bigger problem than it had previously,” says Dr. Darcy Telenko, Field Crop Plant Pathologist and Associate Professor of Botany and Plant Pathology at Purdue University.

She says Randolph County and pockets of east-central Indiana are showing the biggest signs of impact this growing season because of this year’s weather conditions.

“With Tar Spot—initially those spores need a lot of leaf wetness to infect and cause the disease, so in some areas we’ve seen that where we’ve had the right moisture that turned on the disease. Then, the dryness [later in the summer] also made it fluctuate a bit,” she says.

Even though she and her team haven’t confirmed Tar Spot in all 92 of Indiana’s countries, she believes the disease is probably found somewhere in each county.

“We’ve confirmed it in 87 of our 92 Indiana counties because it’s been confirmed in previous years,” she says. “The disease survives year-after-year, so 87 the counties I know have had a previous history of Tar Spot. There are still five that we probably have to get into and find it. I suspect it’s there, but in order for me to turn a county ‘active’ in-season, a good sample or image sent to us at the Purdue Plant Pest and Diagnostic Laboratory (PPDL) can help me confirm it to the county.”

Telenko says that Tar Spot could create a major problem during harvest.

“If Tar Spot has moved in and it’s gotten severe enough, I’d be keeping an eye on some of those fields and making decisions on what fields need to be harvested first as we have seen issues where if there wasn’t a fungicide applied and Tar Spot is very severe, it could increase the risk for lodging.”

“Growers should be getting out now and making an assessment of what the crop looks like, what the canopy looks like, and see if there is risk for lodging to see which fields may need to go first,” she says.

Telenko offers these management tools to mitigate future stalk rot issues:

Properly diagnosis the stalk rot pathogen. (Samples can be submitted to the Purdue Plant and Pest Diagnostic Lab (CLICK HERE for a more detailed description of each stalk rot.)
Select hybrids with resistance if available.
Crop Rotation – rotating to non-host crop will help reduce stalk rot potential in a field. Note that Charcoal rot and Gibberella stalk rot can infect other rotational crops in Indiana.
Tillage – burying infected crop residue will encourage more rapid desiccation and help reduces risk of overwintering in crop residue.
Good soil drainage and reduced compaction.
Foliar Fungicides – applying foliar fungicides can help protect crop from foliar diseases that could predispose plant to stalk rot when present, but devoid of foliar disease pressure fungicides applications have not consistently been found to help reduce stalk rot.

For the 2024 Tar Spot Distribution Map, visit IndianaCropPathology.com.

Dr. Darcy Telenko, Associate Professor and Field Crop Plant Pathologist in the Department of Botany and Plant Pathology at Purdue University. Photo: Purdue Agricultural Communications / Tom Campbell.