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Several conditions can cause kernel set to be less than desirable. The reduction in kernels can occur early in the plant’s life, at pollination, or abort because of other conditions after fertilization.
Extended Rainy or Cloudy Weather. The photosynthetic process can be interrupted during rainfall and significant cloud cover. Should this occur for an extended period during pollination, pollen may not be released when the silks are receptive. This could be evident at different areas on the ear depending on when the stress occurred and which silks were available.
Temperature Variances. Temperature variances just before and during pollination may delay tassel emergence or cause silks to become non-receptive. As an example, temperatures could be relatively warm just prior to tassel emergence and then become very cool when tasseling and silking start.
Insect Feeding. Corn rootworm beetles and Japanese beetles find corn silks very tasty. Clipped silks may not be able to re-grow and become receptive before pollen becomes non-viable with high insect populations and associated silk feeding. Crop scouting can help identify potential insect problems. If thresholds are surpassed, appropriate insecticides may be applied to reduce their effect and help preserve or protect ovule fertilization.
Pollen Desiccation. It is unusual for pollen to desiccate or die prior to successful fertilization of the silks. However, if the plant is under severe heat stress, pollen can dry out and become non-viable.
Figure 1. Ear with a form of tip back.
Kernel Abortion. Aborted kernels appear different than unfertilized ovules. Aborted kernels have a white to yellowish color because starch was beginning to develop in the kernel. Unfertilized ovules have no coloration or development. Aborted kernels can be caused by plant stresses occurring just after pollination. Heat, drought, saturated soils, extreme temperature variances, extended rainy and cloudy days, high night-time temperatures, and fertility deficiencies are among the stresses that can cause tip back or unfilled ear tips (Figure 1). In general, all of these have an effect on photosynthesis and energy production. When energy is reduced, the plant responds by reducing the number of kernels.
Kernel Depth. Kernel depth development after pollination and fertilization is influenced by the same factors that can cause kernel abortion. Shallow kernels could be the result of cloudy days that may have produced ample to above average moisture but reduced the amount of overall sunlight or solar radiation. Sunlight is needed for photosynthesis, which is the process required for starch and sugar production. As an example, Table 1 shows the amount of solar radiation received at West Lafayette, Indiana for the years 2014 – 2016 for the months of July and August. Though 2016 shows more total solar radiation units, a 6-day period from July 3-8 received a daily average of 13.5 units compared to the month’s daily average of 20.6 units.1 This decline in solar radiation occurred during peak pollination and fertilization and may have resulted in unfilled tips. Additionally, a 6-day period from 8/13-18, 2016 experienced a daily average sunlight accumulation of 13.39 units compared to the daily average of 19.32 through 8/26.1 This reduction in absorbed sunlight could result in lost energy and result in shallower kernels.
Figure 2. Kernel depth is a result of many factors including the amount of sunlight during grain fill.
When reduced kernel set is found, regardless of the reason, there is nothing that can be done to change the situation for the current crop. However, scouting and determining the cause(s) may lead to management practices that can help reduce the potential for losing ovules in future crops. Temperature and drought conditions cannot be controlled but tillage, water and fertility management, plant population and spacing, seed product selection, insect control, and timely herbicide application are among the many factors that may help reduce plant stress, improve pollination success, and ultimately increase the number of set kernels. Favorable growing conditions following the loss of kernels may allow kernels to be larger and deeper, which can favorably influence yield potential.
1Atkins, J. Water and Atmospheric Resources Monitoring Program. Illinois Climate Network. (2016). Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495. http://dx.doi.org/10.13012/J8MW2F2Q. Anderson, S.R., Lauer, M.J., Schoper, J.B., and Shibles, R.M. 2004. Pollination timing effects on kernel set and silk receptivity in four maize hybrids. Crop Sci. 44:464-473. Nafziger, E. 2016. “Tip-back” and the 2016 corn crop. The Bulletin. University of Illinois. http://bulletin.ipm.illinois.edu. Larson, E. 2016. Why did the kernels near the ear tip not fill? Mississippi Crop Situation. Mississippi State University. http://www.mississippi-crops.com/2016/07/12/why-did-the-kernels-near-the-tip-not-fill/. Web sites verified 8/21/16. 160831215545