Identifying & Treating Tar Spot

Jul 12, 2021

Tar spots on a corn leaf

All About Tar Spot

With cooler, wet conditions moving into our geography the past week, it is going to be very imporatnt to scout our corn crop for Tar Spot. As the name implies, tar spot can be identified by small black and circular lesions. They are slightly raised, and bumps can be felt on affected plant tissue. Lesions can appear on leaves, husks or stalks and are often surrounded by a light tan colored halo.

Lesions are caused by fungal structures called stromata that cannot be rubbed off affected plant tissues. Symptoms appear most frequently from silking through late grain fill.

Disease development is favored by cool (59°-70°F) and humid conditions (85% relative humidity). Extended periods of leaf wetness over 7 hours also favors disease development. It is believed that tar spot overwinters in corn residue and can be spread via rain splash and wind events. Under severe infestation, where most of a field shows 50% severity on the ear leaf during grain fill, significant yield losses of 20-60 bu/A have been reported. Increased stalk lodging and reduced forage quality in silage have also been reported with this disease. There have not been any reports of associated mycotoxins.
Tar spot spread from 2015-2020

Managing Against Tar Spot

There are several management techniques that can help lessen disease impact. Hybrids differ in their genetic resistance and selecting hybrids with good tar spot tolerance can greatly reduce disease severity. Screening efforts to evaluate tar spot resistance is ongoing. Crop rotation and residue management through tillage can also reduce inoculum loads although research into effects on tar spot is limited.

Several fungicides are labeled under the FIFRA 2(ee) Recommendations for control/suppression of tar spot in corn, including DuPont™ Aproach® and DuPont™ Aproach® Prima fungicides from Corteva Agriscience.
The FIFRA 2(ee) allows for a targeted pest not specified on the label, but does not allow for a change in dosage, application interval, or post-harvest interval. For more information on pesticide labels, please see Preliminary research into fungicide control suggests that VT/R1 through R3 are the best time to make an application.

Contact your local Premier agronomist if you would like your fields to be scouted, or if you have any questions on treating Tar Spot.

Will Tubbs

Retail Product Agronomist
Brevant™ seeds

Latest Posts

Apr 12, 2024

At Premier Cooperative, we provide high-quality fuel solutions for our clients. With this commitment, we're excited to offer you the chance to set up an account to access Cenex premium diesel for your trucks. Here are a few reasons why partnering with Premier Cooperative for your fuel needs makes sense:

Apr 02, 2024
Considering the uncertainties ahead, agronomy management has become increasingly vital this spring. Effective agronomic strategies are key to navigating challenges and maximizing agricultural potential for several reasons: 
Apr 02, 2024
I was caught in a snowstorm coming back from a hedging meeting in Inver Grove Heights, MN on March 26th. It was nice to see that someone is getting a little winter this year. By the time I got to Wisconsin Dells, all of the snow and ice clinging to my truck was gone and I was back in spring weather again. While our propane sales decreased this year, the bright side is that our wear and tear on our vehicles, equipment and employees declined as well. There’s always next year.