Received a number of questions about tip-back in corn and also how the cloudy/smoky days could impact yields. First wanted to mention the difference between pollination concerns vs. tip-back concerns.

Pollination concerns are when the green silk remains attached to the ovule that should have formed a kernel if it had pollinated. Gently husking back an ear and shaking it will reveal where pollination occurred on the ear where the brown silks detach. Green silks remain attached where pollination did not occur. Tip back is when the ovule pollinated but the kernel later aborted (looks shrunken/shriveled) due to some reason, often some type of stress.

This week’s UNL CropWatch shared yield potential for different places in the Midwest using weather modeling and comparing it to a 30-year average. The data clearly shows low solar radiation (which includes photosynthetically active radiation (PAR)), meaning photosynthesis is reduced. In spite of that, the article is suggesting for non-irrigated corn, nearly 100% of above-average yields for the Beatrice area, and nearly 75% chance of above-average yields near the Clay Center and Mead areas. For irrigated corn, it’s estimating 50% near-average yields for Clay Center, 75% near-average yields for Beatrice, and 50% above-average yields for Mead. These estimations are just based on weather and don’t account for stand losses, disease, insects, etc. The full article is at: https://go.unl.edu/tkz6.

Dr. Roger Elmore and Dr. Tom Hoegemeyer wrote a CropWatch article several years ago about the impacts of cloudy days on different stages of corn development. The full article can be found at: https://go.unl.edu/sv06 and the following are excerpts from it.

“Early et al., 1967,…shaded plants around the “reproductive phase” for 21 days as well as during the “vegetative stage” for 54 days and the “maturation phases” for 63 days. Shading during reproductive stages reduced plant yields the most, but 30% shading during the maturation stages ― what we consider the seed set and grain-fill periods (R2-R6) ― not only reduced yield per plant 25% to 30% but also reduced kernels per plant and the amount of protein per plant.  

Researchers in a new study shaded plants from silking to maturity (R1-R6) (Yang et al., 2019). They also found reductions in yield and biomass with more shading resulting in more losses. Shading reduced yields more with higher plant populations than with lower populations.”

If you’re seeing tip-back concerns, it could be due to the consecutive days of cloudy skies reducing photosynthesis. But it’s also important to understand the hybrids in your fields. Hybrids are very specific in how they handle stress such as heat, drought, and cloudy weather during and shortly after pollination. Some hybrids have long ears, and in counting kernels, 30-40 kernels per row with a 1-2” tip-back may be “normal”, especially if there are a larger number of rows around for a decent total kernel number per ear. Plant populations also can play a roll in tip-back. So, not all tip-back is a concern. Knowing the hybrid and counting total kernels per ear can tell a bigger story. We will have to wait and see how the remainder of the grain fill season progresses to better understand any potential yield impacts from the cloudy days.