Fungicide Application Reminders to Optimize Management of Tar Spot and Return on Investment in Corn
Published: 06/14/2024
DOI: doi.org/10.31274/cpn-20240618-0
CPN-2023
The highest and most consistent return on investment (ROI) from foliar fungicide application occurs when fungicides are used for disease management. Fungicide applications may help manage several common foliar and ear diseases. Recent detections of tar spot across the Midwest have prompted the need for a refresher on recommendations for corn fungicide decision-making in 2024.
Tar spot levels in a given field vary based on multiple factors, including hybrid susceptibility, years the disease has been established in an area, and most importantly, how conducive the weather or environment is for disease development. Cultural practices have limited impact on tar spot, and hybrid susceptibility may not be known for all hybrids. Therefore, it is important to be prepared to use a fungicide if needed for tar spot management.
When making decisions on using a fungicide for tar spot management keep in mind:
Fungicide active ingredients are important
Products with multiple fungicide classes are preferred (QoI + DMI or QoI + DMI + SDHI). Products with multiple fungicide classes tend to provide better efficacy and delay the development of fungicide resistance. See the CPN Fungicide Efficacy Guide for specific products and their ratings for tar spot and other diseases.
Application timing is very important
It is best to use scouting and/or tar spot risk or profit tools like Tarspotter and Field Profit to make informed decisions about when to apply fungicides for tar spot management. These apps use weather data to determine if the environmental conditions are favorable for tar spot to develop, and consequently optimize fungicide application timing.
In most years, a fungicide application will not be needed prior to the V10 growth stage.
In most years, one well-timed (VT-R3 growth stages) fungicide will be sufficient to manage tar spot. Even in years where two applications appear to improve tar spot control, improved ROI is marginal over a single well-timed application.
The Crop Protection Network has multiple updated resources available on the latest tar spot research and observations. Check out the CPN TV series on tar spot for more information:
Tar Spot Epidemiology, Model Development, and Decision Support System
Best Practices for Tar Spot Management
Tar Spot of Corn Emerging in New States
Acknowledgements
Authors
Darcy Telenko, Purdue University; Kiersten Wise, University of Kentucky; Alison Roberston, Iowa State University; Damon Smith, University of Wisconsin-Madison; Albert Tenuta, Ontario Ministry of Food, Agriculture, and Rural Affairs; Marty Chilvers, Michigan State University; and Daren Mueller, Iowa State University.
Reviewers
Alyssa Betts, University of Delaware and Travis Faske, University of Arkansas.
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