Make no mistake, when it comes to corn diseases Tar Spot is a booger. Although largely ignored until 2018 in the U.S., the fungus is now generating interest driven by its ability to severely crush corn yields. In fact, some fields suffered yield losses ranging from 25-60 bushels an acre that year.
Especially concerning is the apparent lack of resistance in many hybrids and how quickly it has spread since its arrival. Tar Spot was first identified in Mexico and then the Caribbean before landing in Illinois and Indiana in 2015. Indiana and Michigan reported hot spots in 2019 with appearances reported in Minnesota, Missouri, Ohio, Iowa and even Florida.
“Research is critically needed for rapid development of management strategies to reduce its impact and National Corn Growers Association with the support of state corn checkoff dollars and a FFAR grant is working to begin assessing germplasm for potential sources of resistance,” said Robyn Allscheid, NCGA Research and Productivity Director. “Corn Growers, along with additional support from a FFAR grant, are directing efforts to screen germplasm to look for resistance traits. Five lines have been identified thus far with strong potential.”
Work is also underway to develop a Tar Spotter App for smartphones to assist growers in identifying Tar Spot, relay potential fungicide treatments and to establish economic thresholds for treatment.
The knowledge gained through this project will help our growers better understand the management practices necessary to minimize the effects of this emerging disease, and help our partners identify and/or develop the tools needed to better control this pathogen, Allscheid said.
Tar spot is caused by the fungus Phyllachora maydis and can cause severe yield loss on susceptible hybrids when conditions are favorable for disease. Favorable conditions include wet, moderate weather. We continue to have above-average moisture with saturated, wet field conditions, which are conducive to early-season disease.
Tar spot appears as small, raised, black spots scattered across the upper and lower leaf surfaces. Tar Spot can look very similar to other corn diseases making it critical to identify your problem before treating.
Residue management, rotation, and avoiding susceptible hybrids may reduce tar spot development and severity.