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August 29, 2002

Corn up to its 'droopy' ears in dehydration, agronomist says

WEST LAFAYETTE, Ind. – Water-deprived cornfields look the part all across Indiana. From curled up plant leaves to stalks so weak they're falling over, many cornfields are visibly dehydrated.

Now witness one more sign of moisture deficiency: drooping ears.

It's normal for ears to lean down from the stalk – or droop – as ears become heavy with kernels. But that stage usually occurs after the corn plant has reached maturity and nears harvest. Farmers already spotting droopy ears in fields a month from harvest could be in trouble, said Bob Nielsen, Purdue University Cooperative Extension Service corn specialist.

"Droopy ears are cute on certain breeds of dogs, but droopy ears on corn plants prior to physiological maturity are a signal that grain fill has slowed or halted," Nielsen said. "This premature ear declination – the fancy term for the problem – results in premature black layer formation, lightweight grain and, ultimately, lower grain yields per acre."

Corn ears typically remain erect until the plant passes the black layer development stage, which comes 55-65 days after silking, Nielsen said. At that time the ear shank collapses, causing the ear to decline.

The premature drooping is most likely a result of the exceptionally dry summer, Nielsen said.

"The few times over the years that I have observed this symptom, severe drought stress has been a common denominator," he said. "Similar instances of premature ear declination occurred in areas of drought stress in 1991 and 1995.

"Under severe drought conditions, but where a sizable ear exists nonetheless, a reduction in the turgidity of the ear shank occurs and the weight of the developing ear causes the ear shank to collapse."

European corn borer feeding could be a contributing factor, as well, Nielsen said. As corn borer larvae tunnel their way through the plant, they can weaken the ear shank to the breaking point.

Early ear declination can reduce an ear's grain fill potential and yield.

"The ear shank is the final pipeline for the flow of photosynthates into the developing ear," Nielsen said. "An ear shank that collapses prior to physiological maturity will greatly restrict, if not totally prevent, the completion of grain fill for that ear, and will likely cause premature black layer development in the grain. So if the droopy ears you've seen are not technically black-layered yet, they will soon, because that ear shank has collapsed and the plant is beginning to shut down."

How far ahead of maturity ears droop determines the extent of yield loss.

"If grain fill were totally shut down at the full dent stage of grain development – where the milk line is barely visible at the dent of kernels – the yield loss could be as great as 40 percent," Nielsen said. "If grain fill were totally shut down a little later toward the late dent stage of development – where the milk line is about halfway between the dent and tip portions of the kernel – then yield losses for the affected ears would equal about 12 percent."

A simple mathematical equation can give farmers an idea of yield loss for an entire field. They should multiply the percentage of droopy ears in a field by the estimated yield loss per ear. For instance, a field with 10 percent of ears drooping prematurely at the late dent stage – a 12 percent yield loss – would equal a 1.2 percent field yield reduction (0.10 x 0.12).

In addition to early ear declination, farmers should scout their fields for root and stalk rots, Nielsen said.

"Corn under photosynthetic stress during grain fill tends to cannibalize and remobilize a portion of its stalk carbohydrate reserves to satisfy the physiological demands of the developing kernels," he said.

Carbohydrate concentrations limited by overly dry conditions, combined with plant root systems suffering from heat stress and inadequate moisture, make corn plants attractive targets for soilborne root and stalk rot organisms, he said.

"The inspection techniques are simple," Nielsen said. "Where plants appear to be healthy, dig up a few plants, shake or wash off the soil from the root ball and inspect the roots for obvious discoloration or death from root rot diseases."

After inspecting the roots, "split the lower stalk and look for obvious discoloration or deterioration of the inner stalk tissue," Nielsen said. "Where the plant appearance itself suspiciously suggests diseased stalk tissue, squeeze the lower stalk. If it collapses easily, you've got trouble. If you cannot squeeze it easily, you're probably OK for now."

Fields infected with root or stalk rots should be harvested early to minimize the risk of significant mechanical harvest losses from downed corn, he said.

Additional information for corn growers is available on Nielsen's "Chat 'n Chew Cafe" Web site.

Writer: Steve Leer, (765) 494-8415, sleer@purdue.edu

Source: Bob Nielsen, (765) 494-4802, rnielsen@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

Related Web site:
Purdue University Department of Agronomy

Purdue News Service: (765) 494-2096; purduenews@purdue.edu

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