At the Farm Progress Show held recently at Boone in central Iowa, Iowa State University Extension corn agronomist Roger Elmore was one of the specialists at the ISU exhibit, where he answered farmers' questions about corn production. One of the most often-asked questions he received was about "tipping back."
A lot of farmers in southeast and eastern Iowa this year are seeing "tipping back" of corn ears. That's when the kernels don't fill all the way out to the end of the ear. Those barren tips can reduce the yield in a field - more so than you may realize.
What causes "tipping back" of corn ears? To clarify this discussion, Elmore says tipping back results from either of two possible mechanisms: kernels that were not pollinated in the first place, and kernels that were pollinated but then aborted. Kernels that failed to pollinate could result from late emerging silks, root worm beetle feeding, and/or drought stress coupled with high temperatures during silking. Aborted kernels result from stresses occurring later, sometime around blister stage or milk stage of corn development, he explains. Maybe in late July through mid-August.
In most cases a combination of stresses are the cause
Several different kinds of stresses can result in tipping back resulting from kernel abortion. Dry conditions can cause it, but with the rainy growing season in 2010 that wasn't the cause in most of Iowa this year.
High temperatures are another possible cause of tipping back—and Iowa had some hot temperatures this summer. Foliar diseases also occur about the time when corn is susceptible--late July through mid-August--and they too could help cause tipping back. Cloudy weather and nitrogen deficiency are other possible causes of stress that can induce tipping back. With all the rain Iowa had during the 2010 growing season, that's a real possibility—corn plants were running out of nitrogen.
Also, some fields could have had silk clipping from rootworm beetles. Even something as simple as weed pressure can cause stress on corn plants and help cause tipping back. "Every situation is probably a little different," says Elmore. "But these are things that normally add stress to a corn plant and collectively or individually can cause tipping back."
Early harvested fields are showing disappointing yields
Farmers who've started harvesting corn this past week in Iowa are somewhat disappointed in the yield of their early maturing fields.
That's not surprising, since the fields where the corn has dried down fastest and reached maturity earliest haven't had as much time as they normally do to pack weight into the kernels, says Elmore. Since silking time, the heat unit or growing degree day accumulation has been rapid this year. It's developed the crop and moved it toward maturity a lot faster than normal. "Driving by and looking at cornfields, we noticed there wasn't a lot of green left in a lot of these fields in early September this year," he adds.
Rapid maturity of corn results in lighter kernel weights
The rapid maturing of corn this year will result in lighter kernel weights in a number of cases and also result in lower yields than you may have expected earlier. Does corn with lighter than normal test weight mean it will have quality problems during storage? Along with lighter test weights you can have storage problems, says Elmore. "But probably nothing like the storage problems we had last year in Iowa with the higher moisture contents that went along with lower test weight corn. One of the silver linings this year is that with the early maturity of the corn we have nice, long, warm days to dry the corn down in the field," he notes.
"When dry down rates are faster than normal for corn in the field, we end up with a drier crop than we did last year coming out of the field," says Elmore. "We'll save some propane too, since the grain won't have to be dried down as much with a grain dryer, and that will help shave some cost."