When disease pressure moves into his northeast Iowa cornfields, Aurora farmer Mike Jenks focuses on how to achieve the best spray coverage, dialing in three factors: nozzles, carrier volume and spray intervals.
Jenks says he believes those three things determine whether a fungicide will protect his yield potential — or simply coat the top of the canopy. His approach has support from two of the nation’s highest-yielding corn growers, Randy Dowdy of Georgia and Virginia’s David Hula, who say Jenks’ principles are spot on and apply far beyond Iowa.
“Fungicides work,” Dowdy says. “You just have to get good coverage and be honest about how long they last. What Mike is doing is all about coverage.”
Reconfiguring the Sprayer for 15-Inch Rows
Jenks grows corn in 15-inch rows, which he’s found can increase yield potential. But he’s found the practice also creates challenges with foliar product applications.
“When corn gets tall, that plant blocks the nozzle that’s right over the row,” Jenks explains. “If I don’t adjust, I’m fooling myself about coverage.”
Instead of relying on a standard boom setup, Jenks reconfigures his sprayer before fungicide season. He switches to larger tips for between the rows, directing roughly one-third of the product he’s spraying over the row and two-thirds between the rows to improve penetration through the canopy.
“That’s how we make sure we cover the plant from the soil all the way to the tassel,” Jenks notes.
Dowdy says the strategy matches what modern corn hybrids require.
“Look at today’s leaf architecture,” he says. “From the ear leaf up, a lot of hybrids have a very upright canopy. You’ve got to protect the ear leaf and below. By shifting more of the spray between the rows, Mike is getting coverage throughout the plant instead of just painting the top.”
Coverage Makes the Difference When Disease Hits
That focus on canopy penetration also influences how Jenks views application methods and carrier volumes.
“There were people around us last year who were drone-spraying at lighter gallons,” Jenks says. “They made multiple passes and kept the top green, but they still had disease down low and eventually lost the plant. Coverage is the difference.”
Southern rust put that philosophy to the test last season. Jenks says many nearby fields browned down early while his stayed green longer after a disciplined fungicide program and careful attention to sprayer setup.
“Where we sprayed, it looked like a sea of green,” he says. “Where guys either don’t spray or only sprayed once, they burned up. That tells me the fungicide is doing its job — if I do mine.”
The 16-Day Reality Check
For Jenks, coverage is only half the equation. Timing matters just as much.
He doesn’t expect any fungicide to provide a month or more of protection when disease pressure is at a heavy level. He usually expects to get what he describes as “good protection” for about two weeks.
“If I get 16 days where it really holds, that fungicide’s doing its job. After that, it’s on me to decide whether it’s time to go again,” Jenks says.
Dowdy says the 16 days of performance is consistent with what he observed across the Corn Belt during last year’s southern rust outbreaks.
“There are a lot of companies talking about season-long or four- and five-week control,” Dowdy says. “In the field, when southern rust is really going, about 16 days is what you’re getting, whether it’s a generic product or the premium chemistry.”
Hula sees the same principle in Virginia. While disease pressure differs from year to year, he says growers should focus less on label claims and more on whether the fungicide actually reaches the leaves that drive grain fill.
“Most ‘air tractor’ guys want to spray around a gallon and a half to 2 gallons,” Hula says. “I’m at four-plus gallons per acre because I want to see product reach two leaves below the ear leaf. That’s where yield lives. What Mike is doing with his ground rig is chasing the same goal.”
Farm Journal Field Agronomist Ken Ferrie adds that it’s important to understand the disease you’re targeting and where it’s likely to show up in a given year. For example, homegrown tar spot starts impacting corn plants at the ground level and moves up. Southern rust in the Midwest “blows” in from southern areas and typically infects the crop at the top or even the middle of the plant and will move down. That kind of insight, along with scouting, can help farmers know where to target their foliar application efforts.
Don’t Short-Change Applications With Low Carrier Volume
When field conditions prevent ground applications, Jenks works with aerial applicators, and he pushes for higher carrier volumes whenever possible.
“If the airplane is only putting out a gallon to a gallon and a half, most of that stays on the top leaves,” he says. “I want enough gallons that you can see product at least two leaves below the ear leaf.”
As diseases such as tar spot and southern rust continue moving into more northern corn-growing regions, Hula believes growers should focus on fundamentals rather than expecting any product to overcome poor application.
“Fungicides are tools, not miracles,” Hula says. “The chemistry helps, but coverage, gallons and timing determine whether you actually protect the crop.”
Jenks agrees. His fungicide decisions come from scouting fields, monitoring weather and tracking the number of days since the last application — not assuming the crop is protected because it still looks green.
“The field might look clean today, but that doesn’t mean I’m safe,” he says. “If the calendar, the forecast and my last pass say it’s time to go again, I’m going.”
Be Ready When Pressure Shifts
Dowdy encourages growers to remember how quickly disease pressure can change.
“People get amnesia from one year to the next,” he contends. “In Nebraska, farmers got a taste of South Georgia last year. The jet stream can shift in a couple of weeks, and when that pressure comes out of the Delta, you better be ready.”
For Jenks, every application still has to pay.
“I don’t spray for fun,” he says. “I spray because I’ve seen what happens when the lower canopy gets infected and the plant dies early. When we can keep it green, the combine tells the story.”
Hear the complete conversation Mike Jenks, David Hula and Randy Dowdy shared on the latest episode of Breaking Barriers with R&D at the link below:
