ATLANTA, Ind. – There’s no cure for tar spot but farmers can reduce the potential of drastic yield loss from the nutrient sapping fungus detected in much of the corn belt.

Choosing a hybrid corn plant more resistant to the infectious spores of tar spot and use of fungicides are among the ways to preserve yields as much as possible.

That’s according to Jon Skinner, Regional Agronomy Manager with central Indiana-based Beck’s Hybrid during a Dec. 22 webinar.

The fungus hurts yield by feeding off nutrients required by the plant to fill out the ears.

Skinner said tar spot, carried by the wind and rain in storms, has surfaced most heavily in Indiana, Illinois, Michigan, Wisconsin and Ohio since discovered in the U.S. in 2015.

Tar spot, distinguished by raised dark spots along with orange or pink-like streaks on the leaves and husks of the plant, has turned up on a more limited basis in Kentucky, Iowa and as far south as Georgia and Florida.

“They float a lot further south than what we ever thought they would,” Skinner said.

Skinner said a hybrid fully resistant to the fungus has not been developed. However, the first thing farmers should consider is planting hybrids with greater ability to ward off the symptoms of tar spot.

Skinner advised corn growers to choose a hybrid with a good level of resistance not just to tar spot but other threats during the growing season to avoid being vulnerable to other yield killing sources.

“Look at the total package. Talk to your local seed supplier. Talk to your local agronomist. They can help you find a hybrid that works for your operation,” he said. 

He also recommended farmers scout their maturing fields for tar spot and, if found, start applying fungicide right away no matter where the plants are in growing season.

Skinner said recent studies revealed current fungicides don’t kill tar spot but can slow the rate at which the disease saps nutrients from the plant. The result of fungicide application is more kernels from the disease not robbing the ears of as much nutrients as an untreated plant. Skinner also said fungicides work best against tar spot if sprayed at ground level as opposed to aerial application. Spraying closer to the plant allows the fungicide to settle deeper into the canopy and closer to the ear where it’s needed most.

He said the fungicides also work better at controlling tar spot if irrigating is done more heavily but less frequently during the remainder of the growing season.

Skinner also said tar spot spores, after dropping into the soil during harvest, can survive the winter and can infect future crops over the next several years. 

“If you’ve had tar spot in your area, those diseased spores are going to be present in coming years, depending on environmental conditions, you will see it again,” he said.

Tar spot has reduced corn yield by as much as 60 bushels per acre in severe cases.

There’s also evidence tar spot can weaken the stalks enough to cause the plant to collapse during the season.

Skinner strongly recommended farmers with nutrient starved fields have a nutrient management plan.

If tar spot develops, a plan allows nutrients like nitrogen and potassium robbed from the plant by the fungus to be restored more quickly. 

“If those plants are already stressed, if they’re not healthy to begin with and this disease sets in, that’s where we see the largest yield losses from this disease,” he said.