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Pollinating corn & dry, hot weather

Jeff Caldwell 06/19/2012 @ 9:45am Multimedia Editor for Agriculture.com and Successful Farming magazine.

Though dry conditions stretch from the Plains to the eastern stretches of the Corn Belt, some corn fields appear in greater need of a drink than others. Now, as the crop is entering pollination in some of the biggest corn-growing parts of the country, there are a few key things to look for during this critical time period to gauge whether your corn's reproducing as well as it needs to be, says one corn specialist.

There are several ways drought stress can hamper pollination, says Purdue University Extension corn agronomist Bob Nielsen, whose state of Indiana has seen some of the more severe dryness so far this growing season. First, if your crop should be starting to pollinate but it doesn't appear to have begun, check the silks. They may be there, just not the length they need to be to successfully get ahold of the pollen as it's released from the tassels. This can lead to "nearly barren ears," Nielsen says.

"Severe drought stress can delay the emergence of the silks from the tips of the husks by slowing the elongation rate of the silks. If the delay is too great, silks emerge after most or all of the available pollen has already been shed from the tassels," he says. "Unfortunately, tassel development and maturation often occurs more quickly under drought stress and pollen sometimes is shed prematurely; further exacerbating the problem of delayed silk emergence. Delayed silks not pollinated will continue to elongate until they deteriorate, resulting in unusually long silks."

If the dry spell's been accompanied by extremely hot temperatures so far this spring, dessicated or dried-up silks could hamper your corn's pollination. The silks emerge as normal, but they're too dry to receive pollen.

"Pollen 'grains' cannot germinate on dried, exposed silks and, thus, will fail to fertilize the ovules connected to the silks," Nielsen says. "Again, the result can be barren or nearly barren ears."

Finally, check the tassels themselves. If drought stress is too severe, it can prevent them from emerging completely from that top leaf whorl, so when they pollinate, it doesn't make it to the silks where it needs to go.

"Such failure to emerge completely from the whorl leads to pollen shed occurring within the whorl instead of into the open air," Nielsen says. "If too much of the pollen remains 'trapped' within the whorl for too many tassels throughout a field, there may not be enough pollen left for successful pollination."

Any of these pollination problems can contribute to yield loss in a couple of different ways, Nielsen adds. "Moderate stress often results in barren tips of ears because those kernels are usually last to form," he says. "Severe stress may result in scattered kernel set throughout the ear or odd patterns of kernel abortion like the so-called 'zipper' pattern."

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