“A perfect petri dish of warm, moist air.” This is how NK Seeds agronomist Craig Mackey describes the 2021 growing season in the Eastern and Northern Corn Belt. These conditions proved conducive to above-normal outbreaks of Tar Spot — an agronomic challenge that threatened to rob yield potential from many of the farmers he supported last season.
“No matter where you farm, it’s helpful to know the symptoms and best management practices for keeping Tar Spot in check.”
— Craig Mackey, NK Seeds agronomist
Symptoms of Tar Spot
At first glance, symptoms of Tar Spot resemble tar specks on a leaf or flecks of pepper, although Mackey has observed it on a grander scale, “where it looked like a spray plane sprayed black paint over a field.” These dramatic symptoms are indicators of something less visual, but much more dire. “Where these little black spots hit, they will begin to spread out and shut down the leaf tissue, turning it brown and shutting off the leaf’s ability to photosynthesize or feed the plant,” warns Mackey. “It creates a brown band across the leaf, so everything past that band on the outer part of the leaf may look green, but it’s slowly dying — and when you have a lot of those little black dots all over a plant, every one of those dots is working on shutting down that area of plant tissue, resulting in premature death.”
Tar Spot is known to cause a plant undue stress, taking energy that would have gone into kernel development and resulting in lighter test weights, a less dense kernel or a shorter kernel — all reducing yield potential. The more you know about Tar Spot, the better prepared you’ll be to manage it — so Mackey offers several Tar Spot tips.
Four Tips for Managing Tar Spot
- While there is no one-size-fits-all solution for preventing or mitigating Tar Spot pressure, Mackey says certain management practices can help. Because Tar Spot does not affect soybeans (it only impacts corn and other plants in the grass family), crop rotation is always a good practice, although Mackey cautions that “if the spore opens up and gets in a nearby corn crop, it’s going to continue to grow, under the right conditions.”
- While there is currently a lack of research to pinpoint exactly what makes some treated fields handle Tar Spot better than untreated fields, Mackey says genetics and traits may play a key role. “I’ve witnessed areas of intense Tar Spot where the NK hybrid stays green longer than many of the other brands; NK hybrids seem to handle the load of spores better than the others, which turn brown, lose stalk integrity and show more stalk breakage and kernel shrinkage.”
- Mackey also advises farmers to use fungicides to slow the spread of Tar Spot. He says Miravis® Neo fungicide and Trivapro® products from Syngenta both help farmers keep it at bay. “Both have been very effective at holding Tar Spot back, at least for a while,” he says. “We’ve seen a pretty substantial yield difference between fields that were sprayed and fields that were not sprayed.”
- Despite Tar Spot and other agronomic challenges, Mackey says farmers can feel confident in their decision to plant NK — and hybrid choice matters for defending against Tar Spot and other agronomic challenges. “We like to prove ourselves, and I think we are doing that through our research and breeding programs,” he says. “It’s why NK is the fastest growing seed brand right now.”
These black specks are symptomatic of Tar Spot on a corn plant.
Fastest growing seed brand statement based on the percentage increase in combined corn and soy acres for the top 12 seed companies in the U.S. (by acres planted) from 2019–2021 (2021 corn acres are projected), according to third-party proprietary data.
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