Wallaces Farmer

What's with the twisted corn whorls and yellow leaves that are showing up in some corn fields in Iowa in recent days?

Rod Swoboda 1, Editor, Wallaces Farmer

June 11, 2012

4 Min Read

If you've been looking at your cornfields during the past week, you might have seen some plants with yellowing leaves above the canopy. This symptom is not unusual in fast-growing corn. The leaves should unfurl and turn green within a few days.

That's the summary of the situation, as explained by Iowa State University Extension corn agronomist Roger Elmore, and Mark Licht, an ISU Extension field agronomist in central Iowa. They offer the following explanation and observations.


Fast-growing corn in the last week has resulted in a few scattered plants in some fields in Iowa -- at least in central and west-central Iowa -- displaying bright yellow leaves waving above the canopy (see photo). Corn with these symptoms is around the V5 to V8 growth stage. The yellow upper corn leaves are sun-starved, entrapped earlier in the whorl by more mature leaves. They will wave for a day or more above rapidly growing crop canopies before turning green.

"The symptom is not unusual; we reported it in the ICM News in both 2008 and 2009 occurring at the same growth stages, as well as late as the 10th to 12th leaf stage," says Elmore. "An article posted on the ISU Extension and Outreach corn website also addresses the subject."

Most of the leaves should unfurl within a few days, he says. The pale-yellow leaves will green as they accumulate chlorophyll. "If the deformity causes a delay in either growth or development, it may reduce yield on a plant basis, but the effect - if not widespread - likely will not influence overall yield on a field basis," adds Elmore.

Corn and soybean fields in much of Iowa now hitting rapid growth stage

"Corn and soybean fields across central Iowa have hit rapid growth, especially if they received a sip of rainfall. With the rapid growth two phenomena are showing up," says Licht. "Buggy whipping of V5 to V8 stage corn, and iron deficiency chlorosis of soybeans."


In both cases this is more than likely being caused by rapid growth, he says. In the corn the buggy whipping will go away with some moderate winds and sunlight. The yellow appearance caused by the rapid growth will disappear as the chlorophyll increases in the leaf tissue. End result will be little to no yield penalty on the per acre basis due to low percentage of occurrence."

The iron deficiency chlorosis is magnified by aboveground soybean growth that is more rapid than the root growth, he explains. "With this the solution is hope for some rain and give the plant some more time to catch up. As root growth catches up to vegetative growth the iron deficiency chlorosis will subside. My recommendation is to not drive by those fields for a week or two -- out of sight, out of mind."

Some fields showing K deficiency, even where soil tests optimum to high

Speaking of dry weather, in addition to buggy whipped corn some cornfields are showing a potassium deficiency, even when soil test levels are optimal to very high. "Like iron deficiency chlorosis, chalk this one up to dry conditions," says Licht. "In order for the plant to take up and potassium and transport it within the plant the plant must be able to take up moisture. Fields that had ample moisture during planting and early growth are fine, fields with small or challenged roots from rootless corn syndrome are more likely to be affected."

And lastly, Japanese beetles have hatched and are out in force. "The last couple of days as I've been walking fields, I've been bombarded with Japanese beetles," says Licht. "The hatch is earlier than past years because of the mild winter and early warm up this spring and summer. My warning is to be aware of this pest, keep an eye on defoliation in soybeans and as the corn plant is nearing pollination keep an eye out for clipping of silks. Yet another reason to get out into your fields and take a look."

About the Author(s)

Rod Swoboda 1

Editor, Wallaces Farmer

Rod, who has been a member of the editorial staff of Wallaces Farmer magazine since 1976, was appointed editor of the magazine in April 2003. He is widely recognized around the state, especially for his articles on crop production and soil conservation topics, and has won several writing awards, in addition to honors from farm, commodity and conservation organizations.

"As only the tenth person to hold the position of Wallaces Farmer editor in the past 100 years, I take seriously my responsibility to provide readers with timely articles useful to them in their farming operations," Rod says.

Raised on a farm that is still owned and operated by his family, Rod enjoys writing and interviewing farmers and others involved in agriculture, as well as planning and editing the magazine. You can also find Rod at other Farm Progress Company activities where he has responsibilities associated with the magazine, including hosting the Farm Progress Show, Farm Progress Hay Expo and the Iowa Master Farmer program.

A University of Illinois grad with a Bachelors of Science degree in agriculture (ag journalism major), Rod joined Wallaces Farmer after working several years in Washington D.C. as a writer for Farm Business Incorporated.

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