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Published 17 Sep 2003,Revised images 20 Sep 2003
URL:http://www.kingcorn.org/news/articles.03/TipFill-0917.html
R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen@purdue.edu
ne of the more common complaints overheard in recentdays downtown at the Uptown Bar & Grill has to do with ears of corn thathave not filled all the way out to the tip. Folks walking their fields scoutingfor stalk rot have also discovered ears with one to two inch barren tips.
What are some of the causesof tip fill problems in corn and what are the yield consequences?
Causes
Barren tips of cobs result from some combination of an absence of kerneldevelopment and shriveled, aborted kernels. Each has a different set ofpossiblecauses.
An absence of kernel development indicates that pollination itself wasnot successful. The list of possible causes includes severe silk clipping byinsects (corn rootworm or Japanese beetles) during the final stages ofpollination, delayed silk emergence or deterioration of exposed silks due toexcessive heat or drought conditions, silk emergence failure due to silkballingnear the tip of ear, and lack of viable pollen due to excessive heat or droughtconditions. Diagnosing the exact cause later in the grain fill period can bechallenging.
The occurrence of kernel abortion signals the incidence of severephotosynthetic stress during the first few weeks of grain fill following theend of pollination. Tip kernels are especially vulnerable to abortion becausethey are the result of the final days of pollination and therefore aretechnically the youngest kernels on the ear and most sensitive to subsequentsevere photosynthetic stress.
Factors that can severely limit photosynthesis include consecutivecloudy days, excessive heat and drought conditions (especially when accompaniedby severely compromised root systems), and loss of significant leaf area due tohail damage, severe nutrient deficiencies (think nitrogen this year), severeleaf diseases (e.g., gray leaf spot or northern corn leaf blight), and insectfeeding injury (e.g., grasshoppers). There is anecdotal and some researchevidence that unusually warm nights (mid-70s or warmer) during earlygrain fill periods may also contribute to abortion of tip kernels.
Ear size potential can influence the occurrence of barren tips. Rememberthat potential ear size (number of ovules) is determined early in thedevelopment of the plant, from approximately V6 (six visible leaf collars) toV15. Favorable growing conditions during this period encourages large ear sizepotential, especially in terms of ovule number per row (ear length).
Lengthy potential ears heading into pollination obviously maximize thepotential kernel set and grain yield. Sometimes, though, unusually lengthy earsize results in barren tips if the final tip silks emerge after thefields pollen shed is already complete and thus never receive pollen. Ifpollen is available to pollinate the late emerging tip silks of lengthy ears,the resulting kernels are often dramatically younger than theremainder of the kernels on the cob and, therefore, particularly sensitive tosevere photosynthetic stress.
Yield Consequence
Obviously, absent kernels translate to lost yield potential.Mathematically,for every absent kernel per row on an 18-row corn hybrid (assuming a final earcount of 28,000 ears per acre), the lost yield potential equals about 6 bushelsper acre. Yes, yield loss can mount quickly as a consequence of barren tips.
But, it is also important to make sure you put the problem intoperspective. Before you complain about barren tips to your seed rep, firstevaluate the remainder of the cob. Typical kernel count for harvested ears ofmany hybrids is approximately 600. Hybrids whose ears are typically 16 rows ingirth tend to set about 36 - 40 kernels on each row, while those that typicallydevelop 20 rows of kernels tend to set closer to 30 kernels per row.
The point here is that if potential ear size (number of ovules) wasquite large heading into pollination (favorable pre-pollination conditions) butfailed to pollinate the tip silks, the resulting ears may still exhibit 30 40 kernels per row even though there is one to two inches of barren tip.In other words, harvested ear size will still average about 600 kernels andultimate grain yield will be average to above average.
On the other hand, if kernel counts show only 20 to 25 kernels per rowwith lengthy barren cob tips, then that indeed indicates that the crop sufferedsignificant stress conditions probably more than once during the season. Kernelcounts per ear will be much less than 600 and ultimate grain yield in thislatter example will likely be less than average for that field and/or hybrid.
Click on an image for largerversion.
Acceptable vs. unacceptable tip fill problems
Related References:
Nielsen, R.L. (Bob). 2002a. When and How Can I Estimate CornYields. Purdue Univ. Corny News Network. Available online athttp://www.kingcorn.org/news/articles.02/Yld_Est-0723.html.[URL verified 9/17/03].
Nielsen, R.L. (Bob). 2002b. Yield Loss During Grain Fill. PurdueUniv. Corny News Network. Available online athttp://www.kingcorn.org/news/articles.02/Grainfill_Stress-0802.html.[URL verified 9/17/03].
