Production Blog

Tar spot showed up early this year and has continued to dot the map with positive confirmations. As of July 19, there have been 11 states (Georgia, Iowa, Illinois, Indiana, Kansas, Kentucky, Michigan, Missouri, Nebraska, Pennsylvania, Wisconsin) and Ontario in Canada with positive confirmations of tar spot (Phyllachora maydis).

University plant pathologists are urging corn farmers to not panic, but to continue to scout diligently for the tar spot and weigh fungicide decisions carefully.

The Corn Disease Working Group (CDWG), part of the Crop Protection Network, has developed some excellent tools to help you do that. This week they released a Corn Fungicide Return on Investment Calculator. Find it here: https://cropprotectionnetwork.org/….

The calculator shares results from university uniform corn fungicide trials conducted across 19 states and Ontario between 2019 and 2022. Primary diseases in the data set were tar spot and southern rust.

The treatment cost and expected benefits and breakeven probability values shown in the calculator are estimates based on data and not guaranteed values. The values are also derived from data collected in trials designed to test specific product comparisons. Data are not available for all labeled fungicides on corn.

You can explore more about how the calculator was developed and how to use it at https://cropprotectionnetwork.org/….

CDWG has also developed ratings for how well fungicides control major corn diseases in the United States. A helpful table that reviews many fungicides and how they stack up against the disease can be found here: https://cropprotectionnetwork.s3.amazonaws.com/….

Again, the table is not a substitute for reading the label to determine specific use restrictions, nor does it list every fungicide available for corn disease.

The CDWG determined efficacy ratings for each fungicide listed in the table by field testing the materials over multiple years and locations. Ratings are based on the product's level of disease control and does not necessarily reflect yield increases obtained from product application. A product's efficacy depends upon proper application timing, rate, and application method as determined by the product label and overall disease level in the field at the time of application.

Weather conditions this year have led to a wide variety of pests and pathogens. The Crop Protection Network is an excellent resource for learning about how to tackle all kinds of crop problems. Find the searchable database of information and tools here: https://cropprotectionnetwork.org/….

For other articles from DTN on tar spot go to:

-- "Corn Tar Spot Infections Discovered Early in 2024," https://www.dtnpf.com/…

-- "Watch for Spots, Rots and Crazy Top," https://www.dtnpf.com/…

Need a good way to track tar spot and other diseases? Go to: https://www.ipmpipe.org/… and for tar spot specifically: https://corn.ipmpipe.org/….

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on social platform X @PamSmithDTN

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