Some Current Environmental Conditions Spell Trouble for Some Corn

One of the more common complaints I hear later in the production season after what seems to be good weather for great corn yield is barren tips. Usually, this happens after growers walk into the fields when corn reaches R5 and they discover ears with one to two-inch barren tips. What are some of the causes of tip fill problems in corn and what are the yield consequences?

Barren tips of corn ears result from some combination of no pollination and/or of poor kernel development and/or shriveled or aborted kernels. Each may have a different set of common causes. Possible causes of barren tips may occur during the final stages of pollination, such as delayed silk emergence or deterioration of exposed silks due to excessive heat or drought conditions, silkballing near the tip of ear, and lack of viable pollen due to excessive heat or drought conditions. Silk clipping by insects during the final stage of silking can cause the loss of kernels as well but is somewhat unusual in Georgia. IF there is an absence of kernel development scattered widely across the cob, this is a strong indication of poor pollination likely due to drought OR lack of synchrony of pollen with an active silk (i.e. commonly found on a second ear developing late).

The occurrence of aborted kernels at the tip (1.5 – 2.5 inches) signals the incidence of photosynthetic stress during the first few weeks of grain fill following the end of pollination. Tip kernels are vulnerable to abortion because they set during the final days of pollination and therefore, are technically the youngest kernels on the ear and most sensitive to subsequent photosynthetic stress.

Factors that can limit photosynthesis include consecutive cloudy days, excessive heat and/or drought conditions, loss of significant leaf area due to hail damage, and leaf diseases such as northern or southern corn leaf blight, and/or early southern rust infections and nutrient deficiencies such as nitrogen.

A common event that I have seen in many good hybrids in a decent year are characterized by blond silks on top of brown silks.  This is usually caused by hybrids that have had good growing conditions during the ear development phase (V7 to V14-15) leading to a nice full & lengthy ear size.  In this case, some stress during late R1 will cease silk extension but resume several days later with good growing conditions. This can cause a slight tip growth without kernel development due to lack of pollination.

Georgia is blessed with good ground water and allow us to irrigate much of our crop production.  The majority of corn is irrigated since it is sensitive to stress of short dry spells on our sandy soils.  Frankly speaking, we make some of our highest yields in corn when it is too dry to make dryland corn.  When Georgia corn growers have good rainfall during late May and early June and don’t often need irrigation, then I hear more complaints later in the season with larger than usual barren tips.  Most of the time I can point to the lengthy, cloudy and or rainy conditions as the probable cause during R1 & R2. Fields with populations above 34,000 plants per acre on 36-inch rows are around five inches apart and under good growing conditions will have excellent leaf area resulting in heavy shading during cloudy conditions. Under cloudy/rainy conditions, solar radiation is reduced (obviously) particularly in fields with high plant populations.  Over a few days, this can undermine carbohydrate production leading to stress on the last kernels to develop on the ear. The results may be a 10 to 12% yield difference when compared to years when rainfall occurs earlier or later in the season.

Let examine the yield loss due from aborted or shriveled kernels for whatever the reason. Let’s assume a 16-row ear, 36 kernels per row, final ear count of 32,000 ears per acre & 56 lbs test wt. Given these parameters the yield potential is slightly over 230 bushels per acre. Every lost kernel per row from the assumed ear equals 6 bushels lost. Yes, yield loss can mount quickly as a consequence of barren tips.

It is also important to make sure you put the problem into perspective. The above example is an ear that averaged 576 kernels per ear. A good friend of mine, said “before you complain about barren tips to your seed rep, first evaluate the remainder of the cob. Typical kernel count for harvested ears of many hybrids is approximately 600. Hybrids whose ears are typically 16 rows in girth tend to set about 36 – 40 kernels on each row, while those that develop 18-20 rows of kernels tend to set closer to 30-32 kernels per row.”  His point is that if potential number of ovules are quite large heading into pollination (favorable pre-pollination conditions) yet failed 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, an average harvested ear size will be around 600 kernels and ultimate grain yield will be average. However, if you notice considerable progressive loss of development as you get past 30 to 35 kernels, then those loses may very well be due to lack of light or other factors from poorer growing conditions.

On the other hand, if kernel counts show only 25 kernels per row with lengthy barren cob tips, then that indeed indicates that the crop suffered significant stress conditions probably more than once during pollination or R2-R3 (rather than prolonged, cloudy conditions). Kernel counts per ear will be much less than 600 and ultimate grain yield in this latter example will likely be less than average for that field and/or hybrid.

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