As Ken Ferrie evaluates disease challenges he sees in cornfields right now, tar spot comes to the top of his list of concerns.
“We’ve got a lot of areas that are picking up these 3-, 4-, 5-inch rains, and that’s where you’ll see tar spot really blast if and when it takes off,” says Ferrie, Farm Journal Field Agronomist.
The disease started showing up in central Illinois corn the last week of June this summer, similar timing to what occurred in 2021.
“Last time we had tar spot in June was in 2021, and it really butchered us before it got done,” Ferrie recalls.
While the disease is showing up in Illinois and a handful of other states, the impact so far has been low. But that could change quickly. Ferrie is especially concerned what will happen, now that pollination is almost over for most Midwest corn crops.
“It seems like after pollination, corn gives up some of its disease resistance,” he told Farm Journal’s Tyne Morgan and Clinton Griffiths during their recent podcast, Unscripted. Watch it here:
“The disease pressure really ramps up after pollination compared to pre-pollination, when that corn plant kind of switches to making grain versus being protective,” he says. “I do anticipate that we’ll see a lot more tar spot pressure here, especially in our wet areas, because of the heavy fogs, the humidity in the morning, the wet leaves.”
Charting Average Daily Humidity Can Help
Missy Bauer is also nervous tar spot could take off in Michigan fields this season. She is encouraging farmers to keep an eye on the average daily humidity levels for their area.
“Universities have found when average daily humidity is above 75%, corn crops are at risk,” says Bauer, Farm Journal Field Agronomist and owner of B&M Crop Consulting, Coldwater, Mich.
You can find the average daily humidity information for your specific area online via Weather Underground and other weather station resources.
She says economic data is telling her that a single pass of fungicide at R1 will pay for itself in corn that’s at risk for tar spot. “The data is very supportive of making that first pass, no problem,” she says.
The same data shows a double pass of fungicide often delivers a return-on-investment (ROI), because so many of today’s hybrids build yield through depth of kernel fill. The second pass protects that later-season starch development.
Make sure to watch the brief video Farm Journal’s Matthew Grassi did with Bauer to hear her recommendations on when to apply fungicide to address tar spot, especially her strategy for when or whether to make that second pass.
For an added bonus, Bauer addresses what occurred in soybean fields this spring with the carbon penalty.
A No-Fungicide Decision Needs A Game Plan
Ferrie says he realizes some growers are struggling to make the call to apply fungicides this season, given corn prices.
If you’re still on the fence, he advises making some pre-season yield estimates based on ear counts to help you calculate where an application would help with ROI and where it might not.
In the process, he says to ask yourself these five questions:
1. How well did your crop pollinate?
2. What’s your ear count per acre versus your population?
3. How significant is your disease pressure?
4. Can you harvest the corn crop early, before it falls apart from disease and standability issues?
5. Are you able to dry the crop, if you have to harvest early?
The answers to those questions can help you start to predict what the end result at harvest is likely to be.
“You may have to reevaluate what your yield goal potential is, because if you gave it up at pollination, a fungicide application is not going to get it back for you,” Ferrie says, noting he had that conversation with a grower last week.
“He planned on spraying twice with a fungicide, and now, due to pollination issues, he’s going to only spray once,” Ferrie notes.
If you opt to not spray a fungicide, Ferrie says you need to consider making your contingency plans for harvest now, and you can tweak them as you get closer to running the combine.
“Evaluating your crop now will help this fall and also help you improve what you do next year,” Ferrie says. “Once you’re on the combine, there’s not much more evaluation you can do on a plant-by-plant basis.”
