Southern Rust Moving North, Tar Spot Showing Up More

Southern rust has been making its way north with findings right along the Indiana border in Kentucky and there’s now a probable finding in a Knox County cornfield. That’s according to the distribution map from Purdue Field Crop Pathologist Darcy Telenko’s lab at indianafieldcroppathology.com. They track both southern rust and tar spot to let growers know where those diseases have been found.

“That’s what our clinic is for,” says Telenko. “I would need that leaf sample to confirm it for the state. So, if you think you have it versus common rust, you need to send that sample in.”

Indiana growers can submit corn and soybean samples for free to the Purdue Plant Pest Diagnostic Lab thanks to funding from the Indiana Corn Marketing Council and Indiana Soybean Alliance.

Telenko points farmers to the Crop Protection Network for decision tools on fungicides.

“Southern rust may have some products that rate a little higher for southern rust, that may not as be as high for tar spot or grey leaf spot. And so that’s where you can cross reference. Generally, most of our products will get a good, very good rating, but you can hone in and say, ‘Yeah, I want to use this product because I’m more worried about southern rust than tar spot.’ That’s what those efficacy tables can do; it merges all the university data.”

Telenko joins us on the latest Purdue Crop Chat podcast where we also discuss tar spot, which has been found in 21 Indiana counties as of Wednesday afternoon.

“From our research and regional research, my optimum timing with a single application is at least wait to this VT, tassel-silking stage, and then that window ranges all the way up to R3. That has been my optimum timing if I wanted to pull the trigger for a single application. We’ve also shown that we could go at R4. It may be a little late but there is yield potential there. If you haven’t found the disease and then all of a sudden it comes in at R4 and you’re still at R4, I would still pull that trigger.”

Hear the Purdue Crop Chat where Telenko joins Purdue Extension’s Dan ‘Corn’ Quinn and ‘Soybean Shaun’ Casteel below, or in the free HAT mobile app.