News

Plan accordingly for tar spot

An extension plant pathologist says tar spot is becoming a more common corn disease in Missouri.

The Crop Protection Network says tar spot has been confirmed in more than 20 Missouri counties this year, all north of the Missouri River. And Mandy Bish says the disease has shown up earlier than usual, at low levels.

“They aren’t the levels that warrant the fungicide application, it’s in the lower canopy at low levels.”

She says tar spot needs to progress to the upper canopy to cause yield damage and once the disease progresses past a few lesions, farmers can get a return on investment for fungicide applications. Bish says to save fungicide applications for when the fungus is actively growing.

She says fungicide application between VT and R3 has the best return on investment for managing tar spot, unless “you’re someone along a river and concerned about southern rust and tar spot. If that’s the case, you should aim closer to VT or R1.”

Bish says at least half of the counties that had confirmed tar spot last year have positive cases this year, which means the pathogen has likely overwintered.

“In theory, we can get some of that residue that’s been infected by burying it in the fall. But because this pathogen can move by wind also it’s going to be really hard to reduce the amount of pathogen present over time.”

Brownfield interviewed Bish at the MU Pest Management Field Day.