Orientation of corn ears is not a primary selection factor
Listen up. Some farmers believe erect or upright ears are slower to dry and are more prone to develop ear molds or exhibit kernel sprouting.
Ohio State University agronomist Peter Thomison says there is some truth to the theory. Hybrids that tip the ear down at harvest do not hold water in the husks and might have reduced risk of ear molds. The problem is, you can’t depend on droop.
"Our preliminary results suggest that in addition to hybrid genetics, other factors like varying growing conditions and plant population can affect ear orientation," Thomison says.
Just because a hybrid has a certain ear position one year doesn’t mean it will be that way the next. Thomison says ears of corn normally remain erect until sometime after physiological maturity (black layer development) has occurred, after which ear shanks eventually collapse and ears droop.
However, ears might also droop because they are in drought-stressed fields that have not yet reached physio-logical maturity. A loss of turgidity due to water stress and, perhaps, cannibalization of carbohydrates can cause the ear shank to collapse.
Pioneer Hi-Bred research fellow Mario Carlone actually prefers an upright ear. "For the most part, it indicates the plant is healthy and in good shape. A lot of the time, you get ears tipping down due to premature death [PMD], disease or some other cause that makes the plant die early," he says.
"There’s some give and take here," he adds. "You do have more chance of water collecting and mold in upright ears, but if the hybrid drops its ears too soon, it is a sign that it has given up. Using that as a selection tool means you could be selecting for PMD and poor grain quality due to less grain fill."
Gravity also plays a role, according to Lyndall Dallas, a research agronomist with Dow AgroSciences. "Larger ears are more likely to droop than smaller ears," he says. "Producers should choose hybrids based on yield and yield consistency. In most years, ear size and gravity will take care of the ear position at harvest.
Selection criteria. Prior to Bt technology, resistance to "dropped ears" (where the shucks are still attached to the ear lying on the ground) was a trait that many seed companies used as a selection tool. European corn borers would tunnel through the shank, weaken it and make it more susceptible to dropped ears.
The common use of Bt has all but eliminated this concern. However, says Fritz Behr, a Wyffels Hybrids plant breeder, shank length might have shortened over time as companies selected against ear drop and bumped plant populations.
"High plant populations tend to discriminate against flex-ear germplasm, which tends to have longer shanks, and favor fixed or semi-flex germplasm, which tends to have shorter shanks. However, this can also vary between company germplasm pools," Behr says.
Some of Thomison’s studies have shown that more ears droop when plant populations increase. In other cases, they have stayed the same.
"Today, harvest ear position and shank length are classified as secondary selection criteria," Dallas adds. "While there is evidence that upright ears can lead to fungal ear infections, there is also evidence that fungal ear infections move in through the plant’s vascular system."
Wayne Fithian, Syngenta product lead for technical traits, says that farmers must be careful what they conclude about factors such as shank length and ear orientation. "It’s not that these aren’t important," he says. "But you don’t know what environmental conditions you’ll face next year.
"Pick the hybrid that yields, has exhibited yield stability and the best disease package for your region," he says. "The disease ratings provided by your seed professional are your best selection tool against diseases."
Do you have a question about corn ears? Ask an Agronomist.