Dry weather, excessive heat still choking Indiana corn
By Jennifer Stewart
Much of Indiana's once-thriving corn crop continues to deteriorate as hot, dry conditions continue their stranglehold on much of the state, a Purdue Extension corn specialist says.
The combination of dryness and extreme heat during critical weeks for corn kernel weight development is further cutting into yield potential.
"Plain and simple, the 'frosting is off the cake' for many cornfields around Indiana as dry and often excessively hot conditions continue through the end of this 2013 grain-filling period," Bob Nielsen said. In fact, for some fields, the 'cake' is disappearing, too."
USDA's Drought Monitor update of Sept. 5 showed that about one-third of Indiana was abnormally dry - the lowest level of dryness - while a small swath of the northwestern part of the state fell into moderate drought.
On Monday (Sept. 9), the U.S. Department of Agriculture reported that an estimated 67% of Indiana's corn crop is at the dent stage of kernel development. That leaves nearly one-third of the crop in dough stage, meaning 50% of its yield potential is yet to be determined.
According to Nielsen, there is a common misconception that growers don't have to worry about yield potential when corn has hit dent.
"Once corn reaches dent stage, many folks can be heard confidently stating that there is no reason to worry about further crop stresses because 'the crop is made,'" he said. "Actually, by the time a crop reaches full dent, only about 60% of the crop has been 'made' and there is still 40% of the potential yield on the table yet to be determined."
In fact, corn plants can still fall victim to sudden and complete death as late as two weeks before physiological maturity if conditions are bad enough, Nielsen said. Whole plant death can translate to yield losses as high as 12%.
"A crop is not 'made' until it has successfully reached physiological maturity," he said.
Growers recognize physiological maturity when they can see a thin, black layer at the tips of kernels, which prevents further photosynthate into the grain.
Some of Indiana's most stressed corn plants can be found in soils that have low water-holding capacity or significant soil compaction. Plants in those fields have shown stress in the form of leaf rolling, lower leaf death or whole plant death.
But even crops planted in high-quality soils are showing signs of stress.
"The effects of inadequate rainfall throughout much of the grain-filling period in Indiana and elsewhere have, at times, been amplified by the effects of excessively warm temperatures," Nielsen said. "Certainly not every field of corn is in dire straits at the moment. Certainly there will be fields of corn that yield well or possibly better than they ever have in the past. Just as certainly, there will be fields with significant yield losses due to excessively dry soils and excessively hot temperatures during the past 30 days or so."
Severe stress this late in the growing season, especially during grainfill after successful pollination and kernel set, can cause plants to 'cannibalize' themselves to meet carbohydrate needs of developing grain, Nielsen said.
Corn plants taking stored carbohydrate reserves in lower stalk and leaf tissues and moving them to developing ears can cause weakening of lower stalks and higher risk of root and stalk rots.
"Such cannibalized or diseased plants are naturally more apt to break over or lodge in response to strong winds, potentially turning grain harvest into a frustrating and challenging operation," Nielsen said. "Growers ought to be walking drought-stressed fields during the next several weeks to assess the presence and severity of weakened stalks, then work toward prioritizing the weakest fields for early harvest to minimize the risk of significant mechanical harvest yield losses."
For more information and frequent updates about the corn crop, visit Nielsen's "Chat 'N Chew Café" website at http://www.agry.purdue.edu/ext/corn/cafe/.