For many growers, corn pollination marks a psychological milestone-time to relax before harvest. But agronomists warn that this could be a costly mistake. The critical grain fill period, when starch accumulates in the kernels, plays a crucial role in determining final yield.

Dan Quinn, Purdue Extension corn specialist, cautions against assuming yield potential is locked in post-pollination. "Grain fill is all about kernels filling with starch and becoming as big and heavy as possible," Quinn says. "Managing the crop during this phase-spraying fungicides when necessary, for instance-can extend grain fill and result in significantly heavier kernels."

Mark Jeschke, agronomy manager at Pioneer, echoes this sentiment. He emphasizes that kernel weight, a key yield component, is distinct from test weight-and often misunderstood.

A 2023 field study by Pioneer across nine locations in eastern Ontario confirmed this. One hybrid showed high kernel weight but the lowest test weight, proving the two aren't directly correlated. "A better understanding of kernel weights and what causes them to vary can help in calculating more accurate yield estimates," Jeschke adds.

Facts vs. Myths About Kernel Weight and Yield:

Fact: Genetic advancements in hybrids have improved both kernel number and weight. Modern corn genetics support higher plant populations while extending the kernel fill period, contributing to greater yields.

Myth: Kernel weight correlates with test weight. Pioneer's 2023 data disproves this. High kernel weight doesn't necessarily lead to higher test weight.

Fact: Extending grain fill boosts kernel weight. Purdue trials in both 2022 and 2023-despite different weather conditions-showed that extending grain fill by three to five days increased kernel weight by 10% and yields by 10 to 20 bushels per acre.

Myth: Yield is fixed once corn reaches the dent stage (R5). Not true. According to the Purdue Corn and Soybean Field Guide, kernels at early R5 have only reached about 45% of their final dry matter. Yield remains highly variable-potentially swinging by 30% before reaching black layer.

Fact: Higher plant populations can reduce kernel weight. Pioneer's study observed this trend, though total yield still increased thanks to the favorable growing conditions.

Myth: All hybrids respond the same to higher populations. In reality, hybrids vary significantly in how they balance kernel weight and yield at higher plant densities.

Understanding these dynamics is critical for optimizing yield outcomes. "It's not just about planting the right hybrid or hitting pollination," Quinn says. "Finishing strong through grain fill is where real yield gains happen."