Managing Tar Spot in Corn

By Martin Chilvers

Take-aways

• Understand your hybrids, what are their disease ratings for tar spot, northern leaf blight and gray leaf spot, are any hybrids more susceptible than others
• Scout fields regularly, especially as we come into reproductive stages. The tar spot map is helpful as a guide to scouting, not for timing fungicides.  
• Most years when needed, a single fungicide application from tassel (VT/R1) through milk (R3) provides adequate suppression of tar spot, occasionally an application at dough (R4) will be valuable, very rarely at the beginning of dent (R5).
• Leave a check strip if you are making a fungicide application so you can understand your return on investment (ROI). ROI calculators have been developed to aid in fungicide decision making.
• Use the Crop Disease Forecasting tool (which replaces Tarspotter) to assess risk conditions and to aid in fungicide application timing.

Tar spot this season?

Tar spot is developing yet again this season, with some fields likely requiring a fungicide application. Weather conditions throughout the remainer of the season and hybrid susceptibility will be the primary factor for disease development. Farmers and crop consultants should make efforts to understand their corn hybrid susceptibility and be scouting for disease.