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Narrow down cause of poor tip fill

Corn Pest Beat: Tip-fill issues are not always an insect problem.

June 3, 2020

3 Min Read
5 ears of corn exhibiting poor tip fill
POOR TIP FILL: Experts agree that in some cases, silk-clipping insects lead to poor tip fill. However, there are many other causes, including drought and heat stress. Tom J. Bechman

If we get any kind of stress, my corn doesn’t fill to the tips. Is it because insects clip silks late? What does silk-clipping damage look like? How can I nail down causes of poor tip fill?

The Indiana certified crop advisers panel answering this question includes Betsy Bower, agronomist, Ceres Solutions, Terre Haute; Jesse Grogan, regional manager, AgReliant Genetics LLC, Lafayette; and Stan Miles, agronomist, A&L Great Lakes Labs, Fort Wayne.

Bower: Poor tip fill is typically when at least 1 inch of the corn ear tip has no kernels, or those kernels aren’t fertilized. There are lots of causes. Insect damage is only one cause. Others include asynchronous pollen shed and silking due to severe drought and high daily temperatures, and inadequate pollen supply due to uneven crop development or misapplication of herbicides.

Phosphorus shortages can interfere with pollination. Poor tip fill shouldn’t always be a worry. Certain hybrids always have a bit of empty cob, even if yields are high. Also, good growing conditions could lead to a larger number of potential kernels per row than normal.

If insects are clipping silks, you’ll find a short stub of silk mass at the end of the ear. If they’re a problem, there will be no silks left.

To determine causes of poor tip fill, look at the field as a whole. Check soil phosphorus levels. Note growing conditions throughout the season. Scout for insects at pollination. Poor tip fill could be not just one factor but a combination of factors. It’s tough to diagnose a problem at the end of the season. Most issues can be diagnosed earlier through scouting.

Grogan: Nutritional and environmental stresses are the most common causes. Nutritional stress is usually lack of nitrogen during early grain fill from early-season nitrogen loss. Foliar disease pressure, hail and cloudy weather can reduce photosynthetic activity and cause kernel abortion.

Barren tips could also be due to drought stress, when silks don’t emerge in sync with pollen shed. A plant population that’s too high for field conditions and silk balling also cause barren tips.

Insects usually clip the last silks to emerge and leave the ear tip blank. Kernels aren’t fertilized. Corn rootworm beetles and Japanese beetles are the culprits. Kernel set is economically reduced when silks are clipped less than 3/16 inch from the ear on 50% of plants.

Finding the cause for barren tips is difficult, especially if one waits until harvest. Fields should be checked for insect clipping at flowering time. Timely insecticide applications can reduce economically damaging insect populations. Other causes of barren tips could be observed in the early grain fill stages two weeks after pollination. Adjustments for seeding rate and fertilizer placement could be made in future crops for improved performance.

Miles: Maximum kernel weight per acre should be the goal, and 240 bushels per acre grown on cobs with 1-inch unfilled tips is preferable to 190 bushels per acre produced on fully filled cobs. If adequate populations are achieved, plants should produce enough kernels to maintain maximum yield, even if some ear tips aren’t fully filled.

Under optimum moisture and temperature conditions at flowering, most corn hybrids produce 1 to 2 inches of silk per day. Even though insects may feed on silks, it’s uncommon for this to impact pollination success. Manage very high populations of silk-clipping insects according to established thresholds.

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