Crop Report – Week of September 30, 2024

Ear tip with aborted kernels (shrunk and translucent appearance, yellow embryos visible inside).

Tip Back in Corn

What is Tip Back?

“Tip back” in corn is simply the term used when corn kernels do not form all the way to the tip of the ear.

Tip back made its way into corn discussions this August and September with many commenting that they saw it in more fields this season than in recent years (Figure 1).

Figure 1. Tip back in a corn field in 2024 (photo credit: Josh Kelly).

Figure 1. Tip back in a corn field in 2024 (photo credit: Josh Kelly).

It can be understandably frustrating to observe tip back when scouting a field during grain fill. One can’t help but feel robbed by lost yield potential when they see part of an ear that has not been filled with kernels, or perhaps feelings of a hybrid or field being too lazy.

What Causes Tip Back?

Tip back is usually caused by some combination of two factors:

  1. Failed pollination – ovules (female structures of flowers that eventually form the seed) formed on the ear but failed to be fertilized by pollen.
  2. Kernal abortion – kernels that initiated following successful pollination but later aborted.

Knowing how to diagnose these factors can help provide some understanding as to what has contributed to tip back in a field.

In both cases, it is important to know that the ovules (or kernels following pollination) at the tip-end of corn ears are the most immature. During ear development (starting around V6 or 6 leaf collar stage) ovule initiation and development starts at the base of the ear. Ovules are progressively younger or less developed towards the ear tip. Thus, ovules near the ear tip are the last to form and the last to push out silks from the husks.

What Is Failed Pollination?

Failed pollination is ovules that have not received pollen, and thus do not develop. It is not unusual to find some unfertilized ovules at the ear tip. Fertilization status can be readily confirmed at early grain fill when ovules that have successfully fertilized (received pollen) have silks naturally detach while those that have not fertilized (have not received pollen) will remain attached. Eventually silks for both fertilized and unfertilized ovules will dry and degrade. Unfertilized ovules will remain small and surrounded by glume tissues (the tissues that form red dog or bees’ wings around corn kernels).

What Causes Failed Pollination?

In most cases, these ear tip ovules simply developed too late to have silks emerge in time to intercept viable pollen; they have missed the major pollen shed window. Other silk issues (silk balling, late emergence, insect silk feeding) could cause emergence and pollination issues too (Nielsen, 2003) but these may not be restricted to ear tips.

What Is Kernel Abortion?

Abortion occurs when a kernel that successfully pollinated is later aborted and stops filling grain. Aborted kernels are recognized by their undersized shape or shrunken appearance and translucent or white colouring. On larger aborted kernels, a yellow embryo may be visible inside (Figure 2).

Figure 2. Ear tip with aborted kernels (shrunk and translucent appearance, yellow embryos visible inside).

Figure 2. Ear tip with aborted kernels (shrunk and translucent appearance, yellow embryos visible inside).

What Causes Kernel Abortion?

Kernel abortion is usually observed during earlier grain fill and particularly within a couple weeks of fertilization (Nielsen, 2021). Stresses and insufficient supply of plant photosynthates and other nutrients moved in plant sap (also known as assimilates), are often attributed to kernel abortion. This is thought to happen when the source of assimilates cannot meet the demand of the number of fertilized kernels (also known as the sink). When the source and sink demand are not met, the least mature kernels located at the ear tip will start to abort. This is sometimes attributed to the fact they are the smallest sinks (least competitive) and furthest from the source of assimilates.

While it can be difficult to pinpoint the exact causes of kernel abortion in a field, stress, or loss of photosynthetic activity during early grain fill could be driven by factors such as:

  • Loss of leaf area from physical damage like hail
  • Loss of photosynthetically active leaf area through premature dry down (senescence) of leaves from factors like foliar disease or nutrient deficiencies
  • Reduced or impaired photosynthetic output from weather conditions such as overly cloudy weather, drought or extreme high or low temperatures

Know Your Kernel Counts

In his article, Bob Nielsen (Nielsen, 2003) points out that before we get too concerned about tip back and a loss of potential yield, it would be good to take stock of kernel formation in the field. If conditions were excellent during late vegetative stages, it’s possible a much larger than normal ear could have been set, one we might not expect to fill under normal conditions. In this case, some tip back may not be concerning. If number of kernels in length is much lower than normal (for our given number of rows per ear and ears per acre), perhaps there is more reason for concern for yield limitations.

References

Nielsen, R.L. 2003. Tip fill problems in corn. Purdue University.  https://www.agry.purdue.edu/ext/corn/news/articles.03/TipFill-0917.html (accessed 23 Aug. 2024).

Nielsen, R.L. 2021. Grain fill stages in corn. Purdue University. https://www.agry.purdue.edu/ext/corn/news/timeless/GrainFill.html (accessed 04 Sep. 2024).

Weather Summary: Thursday, September 26 to Wednesday, October 2, 2024

LocationHighest Temp (°C)Lowest Temp (°C)Rain for Week (mm)Rain Since April 1st (mm)GDD0C April 1stGDD5C April 1stCHU May 1st
HARROW       
202424.08.331.5491.7340924923767
202324.511.515.6601.1312022163450
202219.35.72.1431.7325723663677
10 YR Norm (11-20)22.59.720.6556.0324623233699
RIDGETOWN       
202423.07.97.8578.1323323203543
202327.39.17.3515.2298120863237
202220.22.79.5309.5309522113421
10 YR Norm (11-20)22.38.325.1506.0306321433444
SARNIA       
202425.210.411.7491.9325023393546
202326.710.515.8499.3295420593188
202217.82.913.0352.9310122233402
10 YR Norm (11-20)21.79.323.0502.8304521283445
LONDON       
202424.47.36.1591.9321022943530
202326.99.43.0554.6296220673226
202219.23.125.4371.4300721313327
10 YR Norm (11-20)21.78.222.5533.8303121153412
BRANTFORD       
202424.27.76.4492.3314622363445
202327.610.20.2431.3293620403183
202219.61.79.5333.0301521293266
WELLAND       
202424.68.67.9489.8323123163574
202325.310.00.9490.7299320913271
202217.52.44.8400.5307121773417
10 YR Norm (11-20)22.68.327.7479.2305321363444
GODERICH       
202427.76.65.8380.9299120843285
202324.18.90.7371.5277118933002
202220.22.136.0336.6286619933169
10 YR Norm (11-20)20.98.317.6462.8281019033179
ELORA       
202425.05.37.8456.0291920163185
202326.08.20.0470.2272218422917
202218.52.45.8275.7277519022997
10 YR Norm (11-20)20.96.722.8522.7274018373036
MOUNT FOREST       
202424.96.319.6429.0292120213205
202326.09.20.0407.8272118452927
202218.21.729.4415.9276218953023
10 YR Norm (11-20)20.36.821.6530.8273318373063
BARRIE       
202423.95.010.3578.8286719673144
202326.96.20.0501.1272118392931
202219.20.312.8413.1272218452971
10 YR Norm (11-20)20.46.516.9468.3269518022997
PETERBOROUGH       
202424.34.68.9477.0289519913104
202326.92.20.0431.0275918682916
202219.2-2.712.9363.1276118742983
10 YR Norm (11-20)21.65.216.3457.7276518613018
KEMPTVILLE       
202424.46.68.8576.5308521773405
202325.64.10.0508.3293220453139
202218.4-0.77.5514.1292220173191
10 YR Norm (11-20)22.96.816.9515.9290420013231
SUDBURY       
202423.62.210.4556.5273618543009
202326.06.00.0515.4257317292773
202218.2-2.78.4370.0253116842798
10 YR Norm (11-20)19.34.722.4508.4254016972855
EARLTON       
202424.03.79.9549.7267518002895
202324.31.20.6404.1251416702681
202219.7-2.77.7457.3246716302669
10 YR Norm (11-20)19.63.017.9467.9236615462627
SAULT STE MARIE       
202423.44.43.3551.0258016892802
202326.98.27.8386.4253016842710
202219.50.93.6473.8231314692488
10 YR Norm (11-20)19.94.335.2535.8236815262599
THUNDER BAY       
202428.80.50.0345.1248516172658
202330.05.53.9313.9238615642593
202219.1-4.00.0563.3226714582444
10 YR Norm (11-20)18.71.914.1458.1227914462483
FORT FRANCES       
202427.82.90.0490.3257316942793
202329.84.414.5357.7254917202780
202220.3-5.20.0624.7235715492620
10 YR Norm (11-20)18.61.715.1463.2240415532633
Weather Summary compiled by OMAFA using Environment Canada weather station data provided by Agriculture and Agri-Food Canada. Data quality is verified but accuracy is not guaranteed and should be used for general information purposes only.