To Understand The Impact Of Drought And Heat On Corn Pollination

On August 03, 2020

To Understand The Impact Of Drought And Heat On Corn Pollination


We can plant on the optimum date, fertilize exactly as our soil test recommends, have perfect pest control…and then, BAM!  We get whacked with a heat wave or drought period during corn pollination.  Extension Agronomist Dwane Miller reports as the corn crop progresses through its development, it is emotionally painful for a grower to witness corn leaves rolling during any growth period.  However, pollination and fertilization are the most damaging times for the corn to exhibit stress.

According to Bob Nielson, Extension Corn Specialist at Purdue University, there is some good news.  Even in high temperatures, corn will not be stressed severely if soil moisture is adequate.  Heat stress alone will not severely impact yield.  Corn will enter the period of grain yield determination about 2 weeks prior to silk emergence.  If corn is wilting continually due to drought stress, it can decrease yield 3-4% per day.  During silking and pollen shed, this stress can result in an 8% decrease in yield.  2 weeks following silking can see reductions in yield up to 6% per day if drought stress is present.


Silks will begin to elongate from ovules in the ear about 10-14 days prior to silk emergence from the husk.  Silks from the basal (butt) end of the cob will emerge first, with complete silk emergence usually occurring within 4-8 days after the first silks are visible.  Silks will lengthen as much as 1.5 inches per day for the first day or two but will slow down gradually.  They remain receptive to pollen germination up to 10 days after silk emergence.  However, the majority of successful fertilization occurs during the first 4-5 days following silk emergence (Neilson, 2020).  Silks have the highest water content of any tissue in the plant and are most sensitive to moisture levels in the plant.  If there is a severe moisture deficit, the silks may be delayed in emerging.  A lengthy delay may result in the stalk completing pollen shed prior to silk emergence, resulting in barren ears.


If you see visible signs of stress in your fields, it may be from compaction during the wet spring and planting into “less than ideal” conditions.  Shallow root systems will lack the ability to gather soil moisture and will show signs of moisture stress earlier than those with deeply developed root systems.


For more information on moisture and drought stress, read this article written by Bob Nielson at Purdue University.


Figure caption: Corn silks awaiting pollen to complete fertilization (Photo credit: Dwane Miller, Penn State Extension)


To Understand The Conditions That Resulted In Record Wheat Yields


If one could prescribe the perfect growing season for winter wheat in Pennsylvania, it would go like this.  The fall should allow for timely planting, the winter should prevent winter kill to preserve an even plant stand, and spring should be sunny, cool, with no late frost, timely precipitation, and not much fog.  It is very difficult to package all these conditions in one growing season, but in 2019-20 many of these factors aligned, save for a late frost in certain parts of the state that significantly damaged barley stands and moderately damaged some wheat fields in susceptible locations.   The results have been record-breaking wheat yields, often 20 bu/ac above the average condition with yields over 150 bu/ac in some cases.   Why is that? The summary is that we got a long, sunny and cool spring that allowed for spectacular spike and grain growth.

Cool, sunny spring weather serves to increase wheat yields by slowing down the maturation of the plant, giving it more days to absorb solar radiation and convert that radiation into spike and grain growth.  We can also express this as the amount of cumulative solar radiation that occurs during the growth period that brackets wheat jointing, spike growth, flowering, and early grain filling.  When spring temperatures are relatively cool, it takes more days to complete this developmental phase, allowing more solar radiation to accumulate.  This year’s cumulative solar radiation during wheat growth in spring is the highest it has been since 1997.  This enables the survival of tillers which end up bearing fertile spikes.  The second and perhaps most important effect is that wheat spikes become large with more grains per spikelet.  Unlike barley, which also responds to good growing conditions, wheat can have up to 5 or 8 grains per spikelet (or many spikelets with 4 grains instead of 2 or 3 grains) so it can respond tremendously to good weather conditions.  And to top it off, cool and sunny springs lead to effective grain set and longer grain filling.  And all this with the benefit of getting lesser pressure from diseases.  The benefit of cool daytime conditions come with the risk of frost, and a late hard frost did damage barley and some wheat fields in susceptible locations, such as lowlands or west facing positions in the landscape.  It is not often the case in Pennsylvania that we get a sunny, cool and relatively dry spring, but 2020 seems to be a year for the record books in wheat production.

It is possible that certain fields will set the record winter wheat yield for the state, and indeed yield contests have already documented a 153 bu/ac harvest in Lebanon County, 148 bu/ac in Berks County, and two in the mid-130 bu/ac range in Lancaster County.  Across the state, many other farmers are experiencing 15-20 bu/ac yield increases over previous years, consistent with projections from this simple climate model.

We hope farmers and the state can celebrate an exceptional, perhaps record season for winter wheat.  And we also hope that this article helps you to understand and appreciate the climatic factors that aligned to make it such an exceptional growing season.  This is one of those seasons for winter wheat that we hope for, but do not expect to happen very often.  Cheers to those fields with more than 150 bu/ac of wheat, America’s amber waves of grain.


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