(Wanatah, IN) - More is known about treating Tar Spot, but there are no sure fire solutions yet to the still relatively new fungus that cause major losses in corn yields.  That’s according to Darcy Telenko, a Purdue Extension crop disease specialist who gave a report on Tar Spot and other crop diseases August 19 during a virtual field days event at the Pinney Purdue Ag Center in Wanatah.

 

Tar spot first confirmed in the U.S in 2015 was an epidemic in corn fields across Indiana and other states in 2018.  Telenko said tar spot just began emerging this year in a slight percentage of the corn plants at a Pinney Purdue research plot used for developing programs for managing the fungus that migrated here from the south.

 

“We’re beginning to find a few legions of Tar Spot,” she said.  Telenko said now is the time farmers should begin scouting their fields for tar spot so they can formulate a treatment plan before the fungus can start having a major impact on the weight of the ear and development of the kernels in the plants.

 

Tar Spot is known for elevated black spots beginning on the lower leaves before spreading to leaves higher on the stalks.  Telenko said it’s also important farmers know the history of their fields since Tar Spot can survive the winter in debris left behind on the ground following harvest.

 

Telenko said farmers suspecting they have the fungus should scratch the spots on the leaves.  Spots that don’t come off likely means cells from the fungus are embedded already in the tissues of the plant.  She said pictures or samples of the suspected fungus can be sent to the Purdue University Disease Diagnostic Laboratory for verification.

 

Telenko said Tar Spot last year was found in 68 of the state’s 92 counties and about a dozen, so far, this year.  Most concerning is the potential for a major outbreak in northern Indiana since Lake Michigan is a source of the high moisture, lower temperature conditions Tar Spot seems to thrive in the most.  “Around Lake Michigan is where we’re seeing the highest incidents of Tar Spot and that’s where we’re seeing the highest yield impacts,” she said.

 

Telenko said a fungicide can be used to combat Tar Spot but at what stage in a plant’s maturity and other factors on when to begin treatment for obtaining the best results is still under review.

 

Tar spot is also emerging as a growing problem in Michigan, Illinois, Wisconsin and parts of Iowa and Ohio.  She said another fungal disease being closely monitored is Southern Corn Rust found already this year in various areas of the state including St. Joseph County.  “It’s something else to watch for,” she said.

 

Southern Corn Rust generally affects corn after silking and also can severely cut into yields especially in late planted corn.  Telenko said Southern Corn Rust does not survive the winters here.  One of the ways it’s carried here is in major storms moving up from the south, she said.  It usually appears in late June and symptoms include powdery red pustules as spores break through the surface of the leaves.

 

“We want to put those fungicides out when we know we can manage the disease and protect that yield.  We don’t want to go too early because the fungicides may run out of steam when we need later protection at the end of the season,” Telenko said.