News
Corn tar spot from curiosity to serious yield threat
An extension plant pathologist points to fungicides and seed genetics as long-term solutions for managing a relatively new corn disease.
Dean Malvick with the University of Minnesota says tar spot has gone from a curiosity when it was first discovered in the U.S. six years ago to a legitimate threat to farmers.
“We’ve had so little time to really find out which hybrids are truly resistant and to test those that look promising. The data is maybe not as solid as it could be, but that’s certainly going to be a solution. And even now, I think the seed companies know which ones are more (and) less susceptible.”
He tells Brownfield modern fungicides seem to be somewhat effective.
“Getting the fungicides on before we have a lot of infection is going to be important, and in some places they’re asking if they’re going to need two applications. If the disease starts, for example in early August, we might want to get fungicides on then if we see it developing and the weather looks favorable for tar spot.”
But Malvick says there’s some evidence that protection wears thin before the disease tends to really take off in September.
Corn tar spot was first discovered in Indiana and Illinois in 2015 and has spread to Iowa, Kentucky, Michigan, Minnesota, Missouri, Nebraska, Ohio and Wisconsin.
The actual cause of Tar Spot was unearthed by two of us and most or all pathologists are just going down the wrong path. We had the leaf tissue analyzed from from a tar spot infected research plot using an X-Ray scanner and in comparing its symptomology with those in three other crops understand the cause. Fungicides will not treat it successfully unless it acts as an Mn reducer, or unless other things are being included in the fungicide jugs. RAS Iowa 515-709-0143.