News > Co-op News > Tar Spot

Tar Spot

Jul 07, 2025

Tar Spot

Don't Let Disease Sneak in

Crop and weather conditions are aligning for a potentially strong year, making this a season worth investing in. The majority of corn and soybean fields are showing excellent growth and yield potential. However, the consistently high relative humidity over the past few weeks has created ideal conditions, not only for crop development, but also for disease pressure, particularly tar spot. When tar spot reaches 50% severity on the ear leaf during grain fill, yield losses of 20-60 bu/ac have been reported. 

What to Know About Tar Spot

  • Caused by the fungus Phyllachora maydis

  • Looks like small, raised black circular lesions on stalks, leaves, and husks
    (These spots cannot be rubbed off)

  • Most frequently appears between silking and late grain fill

  • Can overwinter on infected residue left on the soil surface

Favorable Conditions for Tar Spot

  • Cool temperatures

  • High humidity

  • Prolonged leaf wetness

  • Irrigated fields are especially susceptible

Confirmed presence in PA, IN, IL, IA, MO, KS, NE, and now WI means this disease is active and spreading. See where tar spot has been reported here: https://corn.ipmpipe.org/tar-spot/

We recommend evaluating your fields now, especially if you’re nearing V10 or have a history of Tar Spot pressure. If you’d like help scouting or building a fungicide plan, our agronomy team is ready. Contact your Premier agronomist today to get started. 

Greg Ballweg

Agronomist

Latest Posts

August 2026 Energy
Jul 31, 2026
Now that August is here, I’d like to welcome the employees and patrons of Farmers Union Cooperative to Premier Cooperative. We’re looking forward to working with you and providing you with safe, reliable, and high-quality fuels and lubricants.
Gearing up for Harvest
Jul 31, 2026
Harvest season is nearly here, and now is the time to get prepared. Whether you’re managing grain contracts or reviewing your records, having the right tools in place can make a big difference. Two key resources to help you stay organized and efficient this season are our member login and a solid understanding of your contracting options.
Tub Recycling & Chipper Days
Jul 31, 2026
Empty feed tubs piling up? Don't let them collect dust, bring them in and give them a second life! Join us for a Tub Recycling & Chipper day, where you can recycle your used plastic tubs and take advantage of on-site silage moisture testing.

Related Topics

General
Agricultural
Residential
Commercial

Related Posts

Premier Co-op
Propane Tank

August 2026 Energy

Now that August is here, I’d like to welcome the employees and patrons of Farmers Union Cooperative to Premier Cooperative. We’re looking forward to working with you and pro...

Jul 31, 2026
Premier Co-op
Bins

Gearing up for Harvest

Harvest season is nearly here, and now is the time to get prepared. Whether you’re managing grain contracts or reviewing your records, having the right tools in place can make a b...

Jul 31, 2026
Premier Co-op
Mineral Tub

Tub Recycling & Chipper Days

Empty feed tubs piling up? Don't let them collect dust, bring them in and give them a second life! Join us for a Tub Recycling & Chipper day, where you can recycle your used pla...

Jul 31, 2026
Premier Co-op
Premier Logo

From the Manager's Desk

August is an exciting month for Premier Cooperative as we officially welcome the members, employees, and communities of Farmers Union Cooperative into the Premier family.

Jul 31, 2026
SEE ALL CO-OP NEWS