Dry weather took icing off corn yields

Much of the state’s once thriving corn crop took a late-season yield hit as hot, dry conditions developed in late summer.

The combination of dryness and extreme heat during corn kernel weight development is further cutting into yield potential. Purdue University corn specialist Bob Nielsen said that these conditions took the “frosting off the cake” in many fields that were making a final push to fulfill their full yield potential as the hot and dry conditions developed.

“In fact, for some fields, the ‘cake’ is disappearing, too,” he said.

The U.S. Department of Agriculture’s Drought Monitor update of Sept. 5 showed that a small area in western Ohio was abnormally dry — the lowest level of dryness. While most of the state was not in any level of drought after the soggy conditions for much of the growing season, there were many other areas that were getting fairly dry. Some areas in northwestern, central and southern Ohio went for two or three weeks with very little rainfall in August and early September. USDA numbers showed that, by Sept. 9, along with very warm temperatures, every part of the state had started to fall behind on average weekly moisture, despite the ample moisture earlier in the growing season for many areas.

The 2013 percentage of Ohio corn in full dent has been lagging behind the five-year average and 2012, but caught up with the five-year average by Sept. 9. At that point just over 60% of the state’s corn was in dent, but the corn had been enduring very dry conditions for several weeks in pockets of western Ohio.

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. Corn plants in the most-stressed fields have shown stress in the form of leaf rolling, lower leaf death or whole plant death, which can lead to stalk lodging, stalk rots and additional harvest challenges.

But even crops planted in high-quality soils are showing signs of stress.

“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,” Nielsen said. “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 harvest to minimize the risk of significant mechanical harvest yield losses.”

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