Two more (Kansas) counties were added to a growing list of Tar Spot confirmed areas across the Corn Belt. Jefferson and Nemaha Counties were added, as were neighboring counties in SE Nebraska (Richardson) and NW Missouri (Platte). To date, most disease pressure is very light, but scouting should continue (follow confirmations at: https://corn.ipmpipe.org/tarspot/)
What now? An excellent synopsis of the current situation is provided in this week’s KSU Agronomy eUpdate from K-State Research & Extension Row Crops Pathologist Dr. Rodrigo Onofre at: https://eupdate.agronomy.ksu.edu/article/update-tar-spot-is-now-active-in-four-counties-in-northeast-kansas-597-6 . It will provide answers to a lot of the questions you are likely mulling over as we prepare to make treatment decisions.
I would also add a couple of additional thoughts/references to consider…
Know What You Have
Some of the black spots on corn leaves are Tar Spot – but likely not all. In the early stages of the disease, bug droppings and other material have a similar appearance to Tar Spot but are not. Check by taking a small bit of moisture on your finger and trying to rub the spot off. Tar Spot will not rub off.
If in doubt, let us know! Images can e-mailed to me at dhallaue@ksu.edu or reach out via any Meadowlark Extension District Office for other submission methods, including The KSU Plant Pathology Lab. Submission can be made through the office or via the lab information included in the article above.
Fungicide Selection – How do I make the best decision?
In the post below is an image of a fungicide efficacy chart courtesy of the Crop Protection Network. It’s a great cross reference of products with efficacy ratings based on input from many of years of plant pathology expertise across the Corn Belt. Check it out before you make a fungicide decision.
When should I apply?
Dr. Onofre outlines suggested fungicide timings in his eUpdate article including a link to the KSU Corn Growth and Development Poster with this statement:
Research has shown that making an application just after first detection and at or after VT is effective if lesions are detected early. If you wait until there is significant disease in the upper canopy, a fungicide application may be too late.
Want additional information on application timing? This article from Dr. Mandy Bish at the University of Missouri is a good one: https://ipm.missouri.edu/croppest/2024/6/tar_spot-mb/?fbclid=IwZXh0bgNhZW0CMTEAAR1Veg8A-w90opxILQYOk5_GLw-dFxbF0AJ74fELPskmX9u8Xha2W-gb9mo_aem_ZmFrZWR1bW15MTZieXRlcw . She shares information from a study that separates application timing differences between seeing a yield response and seeing a return on investment to the application.
Keep in mind: you have +/- 12 days from silking (R1) to blister (R2) and by three weeks after silking you are at R3. That seems like a wide window – until it’s not. Plan accordingly!
Are Other Diseases a Concern?
They sure could be and fungicide application timing needs to be considered in light of pressure from those other diseases as well. Scouting will be important to stay ahead of damaging levels of Gray Leaf Spot, Common Rust, and Southern Rust as well – even if Tar Spot doesn’t become a huge issue. NOTE: as of this writing, Southern Rust has NOT yet been detected in the United State according to the Corn ipmPIPE page dedicated to Southern Rust.
Want to Dive Deeper?
- If you want a deeper look into some interesting work comparing early AND late fungicide applications, check out this recent video from Purdue’s Darcy Telenko: https://www.youtube.com/watch?v=qObD-ld9G88 .
- If product efficacy information is of interest, another video from the Crop Protection Network shares multiple years of efficacy information from the fungicide working group: https://www.youtube.com/watch?v=CI62h71g6qQ . The 2023 data starts at around the 20:00 mark.
Tar Spot continues it’s move and fungicide application decisions will soon be upon us. Feel free to reach out if you have any questions!
