So far, the corn crop in Iowa has clipped along, with timely planting supplemented by late May and early June rainfall in many areas. Farmers in parts of Kentucky, southern Indiana, Ohio and Missouri, however, haven’t been as lucky.
“There are parts in those states that were hammered by rain that made it challenging to get the crop in the ground,” says Andrew Penney, Preceon agronomy lead for Bayer Crop Science.
Now what?
Like a football coach who makes halftime adjustments, now’s the time to make adjustments for your corn as it heads into the second half of the 2025 growing season. Using a proactive approach rather than a reactive one can help corn withstand growing season challenges, Penney says.
In the case of nitrogen, sidedressed applications as early as V8 or around tassel (timing hinges on fall or spring N rates) can supplement N applied in fall and early spring that may have been lost to leaching and/or denitrification from early wet conditions.
Another factor driving the odds of a supplemental N payoff includes a shift by farmers to planting later-maturing hybrids. Later-maturing hybrids pack more yield potential than earlier-maturing ones, mainly due to additional kernel weight that they pack on.
“Having nitrogen available later in the growing season can help pack weight on those kernels,” Penney says.
Longer-maturing hybrids can better withstand stressors — such as heat — better than earlier-maturing ones.
“A week of stress doesn’t have the same impact on a 116-day product as it does with a 108-day one,” Penney says. “Typically, later-maturing products have longer vegetative and reproductive growth. A stressful period doesn't have the same impact on them as it does on shorter-maturing hybrids.”
Hybrids with later maturities also tend to have a better genetic background to tolerate high heat and drought scenarios.
“I always like to say those late-maturing products are a kind of heat and drought insurance,” Penney says.
N needed as late as R5
To realize this added yield potential, adequate N is a must.
“We need nitrogen later in the growing season, through the reproductive stages,” Penney says. At R5 — a growth stage in which kernels are beginning to dent — 40% to 45% of a corn kernel’s dry matter is still accumulating, he adds.
“The more we can do to ensure that we have nitrogen available for that plant later in the growing season, the better off that crop will be,” Penney says.
Application timing is complicated, though. Although moisture can trigger N losses from denitrification or leaching, it also can raise soil N rates via mineralization, he says. Later on in the summer, dry weather can slow mineralization. Conversely, droughty conditions can nix N losses from leaching and/or denitrification.
“What I tell growers is that sometime during the year, we will have some adverse weather, whether that's extreme drought or extreme moisture,” Penney says. “When you look at the weather in the last three to four years, we've either been extremely dry or extremely wet. Either one doesn’t bode well for having nitrogen available later.”
Thus, he advises sidedressing N at the V8 to V10 stage or tassel stage. Timing depends on fall, spring or starter-applied N. This will help corn create the heaviest kernels and most ear kernels possible, Penney says.
Tar spot travails
The ominous irregular black spots on leaves, stalks and husks that signal a tar spot infestation seem a distant threat. Still, this new fungal disease struck as early as V10 in southwestern Indiana last year, says Madison Wozniak, an FMC technical service manager. Left unchecked, yield losses of 20 to 40 bushels per acre have resulted in experimental field plots when 50% of the ear leaf was covered in tar spot stromata (fruiting structures) at R5, says Alison Robertson, Iowa State University Extension plant pathologist.
Corn-after-corn fields can have high levels of inoculum due to high residue levels. In the end, though, all cornfields can be at risk, as inoculum can move into cornfields rotated with crop such as soybeans, Penney says.
“Spores can blow from county to county and potentially state to state,” he says.
Genetic resistance remains the best way to manage tar spot, Penney says. In-season, fungicides are an excellent management option.
Timing, however, is critical to maximize return on investment, he says. ROI can change according to weather conditions, Penney says.
Dry weather one to two weeks before tasseling that continues makes it advantageous to delay fungicide applications, Penney says.
“If we are dry a week or two before tasseling and the weather remains dry, the chances of having a fungicide give the best ROI are not as good as it is under high humidity and high moisture-type environments,” Penney says.
If dry weather extends into R2, a fungicide application can help protect the plant on the backside as it fills the remaining 40% to 45% of dry matter to ensure the heaviest kernel weight possible.
“That’s when having your own sprayer can open the door to letting Mother Nature dictate when that application is made,” Penney says.
Still, tassel time remains the best application time for farmers who depend on custom applications. This helps ensure a timely application can be made, particularly if wet conditions surface and accelerate the disease, he says.
Slay stubborn weeds
Another perk of this year’s almost picture-perfect planting season is that farmers had ample time to apply preemergence residual herbicides. Sufficient rainfall also activated them.
On the other hand, farmers in wet areas may struggle with making postemergence applications. Meanwhile, weeds continue to grow unchecked.
“This is the time to start thinking about bumping up label rates [while not exceeding label rates] and perhaps using an additional product or a [labeled] adjuvant that might be hotter,” Penney says. “Typically, we want to shoot to control weeds that are 3 inches tall. By the time they start getting pop-can size, they can get challenging to control.”