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Understanding corn rapid growth syndrome
This unusual occurrence is often misdiagnosed, but it typically has minimal yield impact.
Abnormal corn growth can quickly concern farmers, prompting them to check fields for causes and solutions to avoid yield loss.
Rapid Growth Syndrome (RGS) is one such odd phenomenon. It can occur during great corn-growing weather from the V5 to the V11 growth stage, and sometimes as late as tasseling. When fast corn growth occurs, and new leaves can’t emerge from a tight, twisted whorl, misdiagnosis can send farmers down the wrong rabbit holes.
The best course is to be patient and let nature unfurl this issue in a few days. You’ll see yellow leaves after unfurling, but they green up rapidly, and yield loss rarely occurs.
Weather and genetics
“We see this phenomenon fairly frequently, usually attributed to really good growing conditions during warm weather with good soil moisture and good fertility,” said Mark Licht, Iowa State University Extension cropping systems specialist.
This physiological condition occurs when leaves fail to unfurl normally. The whorl becomes tightly wrapped or twisted as new leaves grow faster than older leaves can open. It’s not caused by disease or insects.
Hybrid genetics can definitely play a role, as certain characteristics make some hybrids more susceptible to the syndrome. “The challenge is that we still don’t have this syndrome totally figured out,” Licht admits.
In 2025, he saw cases of RGS that bucked the norms previously seen. Flag leaves wrapping around tassels and the lack of cooler weather that usually precedes a fast-growth period were two unique occurrences.
Herbicide injury misdiagnosis
Symptoms of RGS are sometimes mistaken for plant growth regulator herbicide injury from 2,4-D, dicamba, acetochlor or others.
Herbicide injury can result in twisted whorls due to rapid cell elongation, often in areas of sprayer overlap where plants receive a higher rate.
“The biggest difference is that Rapid Growth Syndrome rarely affects more than 5 to 10% of randomly scattered plants in a field. Herbicide injury would be more consistent plant to plant and repeatable within sprayer patterns,” Licht said.
Field signs
RGS often occurs when a warm period follows cooler temperatures. The fast-growing new leaf gets trapped in the whorl and can’t emerge, causing the entire whorl to bend and twist as leaves try to force their way out.
A good telltale sign of RGS is yellow leaves that appear after the whorl grows and releases the trapped new leaves. With sunshine, even those symptoms will disappear within a week or sooner. The remaining telltale sign is that leaves may still appear wrinkled or crinkly along the edges after unfurling.
Licht encourages growers to note which hybrids exhibit symptoms, then examine the same hybrids in other fields. Symptoms may not appear elsewhere due to weather and crop differences.
“We’ve noted susceptibility to RGS across numerous hybrids from multiple brands, so the issue isn’t brand specific,” he said. “Some hybrids appear more prone than others, but this depends on the interaction between genetics, maturity selection and planting date.”
Remedies and yield
Missteps can occur when growers see leaf yellowing and think a fungicide or some other product is needed to address it. Licht recommends waiting several days because most of the time, the newly unwrapped yellow leaves will green up.
Since the impact from RGS is usually less than 5%, the yield loss is near zero. “I’m sure there may be a tiny amount of yield impact because that whorl is wrapped up, which limits photosynthesis for a brief period. It’s just never been a loss we’ve been able to detect,” Licht said.
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