Tar spot’s impact on corn hinges on the timing of rain – that was one of AgriGold Agronomist Kevin Gale’s main takeaways this season. “For tar spot to have an economic impact, we learned you have to have pounding, spore-splashing rain early – in late May or early June,” he says. “That infection early in the growing season can result in the development of tar spot during grain fill.” 

Rains didn’t move into his territory of northern Illinois and southern Wisconsin until late June, so tar spot arrived too late to have much of an impact. Farmers in other areas of the country, like central Iowa, northeast Kansas and south-central Illinois, weren’t as lucky; they observed tar spot much earlier in the season.

Regardless of how you fared this season, tar spot will remain an annual threat. “Tar spot has shown up every year since its 2015 introduction to the Corn Belt,” Gale says, noting the disease’s ability to overwinter. “Farmers need to remain vigilant and ready to manage the disease if conditions are conducive to its development. Fortunately, we have hybrids and management techniques to help.” 

Corn hybrids are farmers’ best defense against tar spot

Hybrid selection should be a farmer’s No. 1 defense against tar spot, according to Gale. While no hybrids are resistant to the disease, some are tolerant. AgriGold includes tar spot tolerance ratings in its seed profile guides. 

“As farmers deal with tar spot year after year, they are increasingly looking for products with higher tolerance to tar spot,” Gale says. “Planting tolerant hybrids can provide peace of mind they won’t get hammered in heavy infestation years when tar spot can cost farmers up to 60 bushels an acre.”

AgriGold groups hybrids into genetic families based on both their underlying genetics and agronomic characteristics. Of the genetic families planted in his area, Gale reports Field GX™ Family B hybrids offer the best tar spot tolerance. “Hybrids such as A636-16, A638-19, A643-37 and A644-19 have provided higher tar spot tolerance,” he details. 

Scout fields to protect crops and prepare for next season

Fungicide applications and crop rotation can also limit tar spot’s impact, according to Gale. He ranks fungicide as the second most important management tool. Scouting for tar spot and other threats is also a must. 

“Now is a great opportunity to scout your fields and see how your hybrids held up to diseases like tar spot,” Gale says. “If you’re starting to see some disease show up, you may need to prioritize which fields you harvest first.”

His main concern heading into harvest is stalk quality, given an array of stressors including Fusarium crown rot infection, potassium deficiency and anthracnose, along with drought and heat stress. 

“From a disease standpoint, tar spot has not presented many issues in my territory this year,” Gale says. “But next season could be entirely different.”

To make sure your hybrid portfolio includes protection against tar spot, reach out to your local AgriGold agronomist or district sales manager.