Key Takeaways

• Weather raises grain quality concerns. Wet conditions late in the growing season have increased concerns about kernel sprouting, ear rots and grain quality in Nebraska corn.

• Check for multiple problems. Insect damage, premature kernel sprouting (vivipary) and ear rot diseases can occur together, making field scouting and accurate identification important.

• Manage affected grain carefully. Prioritize early harvest, dry grain appropriately for its intended storage period and monitor stored grain closely for mold, hot spots and additional sprouting.

Warm, wet weather in September has raised concerns about corn grain quality as harvest gets underway across Nebraska. While some producers have begun harvesting, others are still waiting for fields to dry enough to support equipment. Reports of sprouting kernels (vivipary) and ear rot diseases are already emerging in parts of the state (Figure 1).

September was historically warm and exceptionally wet across portions of Nebraska. Lincoln and North Platte experienced their fourth-warmest September on record, with average temperatures of 73°F and 69°F, respectively. Omaha recorded its second-warmest September, averaging 73°F. Rainfall totals ranged from 1 inch to more than 10 inches across eastern and south-central Nebraska, with daily precipitation records set in Grand Island, Hastings, McCook and Lincoln. Lincoln recorded 11.49 inches of rain, making it the wettest September in 140 years and exceeding the monthly average by 8.59 inches.

Insect feeding damage has also contributed to grain quality concerns this season. High populations of western bean cutworm (WBC) (Figure 2) and corn earworm (CEW) have been reported in Nebraska fields, increasing the risk of ear rot diseases. Although ear rot diseases are caused by fungi, feeding damage from these caterpillars creates wounds in husks and kernels that allow the fungi to enter and infect developing ears.

Premature Kernel Sprouting (Vivipary)

Vivipary occurs when corn kernels germinate and begin developing into seedlings while still inside the husk and attached to the cob. This can happen when kernels that have dried to less than about 20% moisture are exposed to additional moisture during warm weather. Ears that remain upright on the plant are especially susceptible because rainwater can collect inside the husks, causing kernels to sprout near the base of the ear.

Vivipary can reduce overall grain quality, and sprouted kernels are more susceptible to insect infestations and fungal growth, particularly during storage. If a large percentage of kernels are sprouting, it may be necessary to prioritize harvest in the most severely affected fields and dry the grain to less than 14% moisture before storage to help prevent further quality deterioration.

Ear Rot Diseases

Several ear rot diseases have been identified in Nebraska fields and in samples submitted to the UNL Plant and Pest Diagnostic Clinic (PPDC), including Fusarium, Gibberella, Aspergillus, Diplodia, Trichoderma and Penicillium (see Nebraska Extension NebGuide EC1901, “Corn Disease Profile III”).

Many of the affected ears and plants submitted to the clinic had also sustained damage from hail or ear-feeding insects. These injuries create openings for fungi to infect the ears, contributing to disease development. Some of these fungi can continue growing as grain molds during storage, further reducing grain quality.

Cooling and drying grain are important steps for limiting mold growth during storage. For short-term storage, drying grain to 15% moisture can help slow fungal growth. However, grain intended for long-term storage, particularly through warmer months, may need to be dried to less than 13% moisture to maintain quality.

Scouting fields before harvest can help producers identify grain quality concerns and determine which fields are most severely affected. This information can guide decisions about harvesting, storing, marketing and using potentially contaminated grain.

Aspergillus ear rot is caused by several species of Aspergillus fungi, including A. flavus, A. parasiticus and A. niger. The disease typically appears as olive-green, powdery masses of spores on kernels, particularly near exposed ear tips or areas damaged by insects or other injuries (Figures 3a and 3b). The appearance of infected ears and their potential for mycotoxin contamination can vary depending on the fungal species involved.

Hot, dry weather, wind and feeding damage from western bean cutworm and corn earworm can increase the risk of infection. Corn that experienced drought stress earlier in the growing season is particularly susceptible, including non-irrigated fields and drought-stressed corners of pivot-irrigated fields.

Gibberella ear rot is caused by the fungus Gibberella zeae (the sexual stage of Fusarium graminearum). The disease typically begins at the tip of the ear, appearing as white, pink or reddish mold (Figure 4). As the disease progresses during grain fill, the mold may spread toward the base of the ear.

The fungus can also produce mycotoxins, including deoxynivalenol (DON), commonly known as vomitoxin, and zearalenone.

Fusarium ear rot is a common disease caused by Fusarium verticillioides that appears as white, cottony patches of mold anywhere on the ear, particularly around wounds caused by insect feeding or hail. Infected kernels may also develop a distinctive starburst pattern on the kernel cap (Figure 3b).

The fungus can produce fumonisins, a group of mycotoxins that may be present even when there are few visible signs of infection.

Diplodia ear rot is caused by the fungus Stenocarpella maydis (formerly Diplodia maydis). Warm, wet conditions favor disease development, particularly when rainfall is above average between silking and harvest. Losses may be greater in years with above-average rainfall between silking and harvest or when insect or bird damage occurs.

The disease typically appears as dense, white mold that begins at the base of the ear and spreads toward the tip. Infected ears can quickly become covered in mold, eventually drying out and becoming lightweight or “mummified” (Figure 5).

Unlike some other ear rots described here, the fungus causing Diplodia ear rot has not been reported to produce mycotoxins in the United States.

Management Options

• Harvest early: Prioritize early harvest in fields showing significant ear rot or kernel sprouting to help limit further grain quality losses.
• Dry affected grain. Dry affected grain to a moisture level appropriate for the intended storage period. Higher drying temperatures may be necessary when managing sprouted kernels (vivipary).
• Screen out fines. Screen grain to remove fines and damaged material that can contribute to storage problems.
• Monitor stored grain. Watch closely for hot spots, mold development and additional sprouting.
• Scout for ear-feeding insects. In future growing seasons, monitor fields, especially during the V14-R1 growth stages, and implement control measures when pest populations reach the recommended action thresholds to minimize kernel damage and ear injury (see the CropWatch articles "Degree-Days for Prediction of Western Bean Cutworm Flight in 2026" and "The Biology and Management of Ear-Feeding Lepidopteran Pests of Corn in Nebraska").

In general, producers should prioritize selling or using the most heavily affected grain before its quality deteriorates further, while reserving the highest-quality corn for storage. Feeder cattle may be an option for using some loads of affected corn.

Keep in mind that ethanol plants may have lower tolerances for mycotoxin concentrations. During ethanol production, starch is removed for fermentation, which can concentrate mycotoxins threefold or more in the resulting distillers grains. These higher concentrations may exceed safe feeding levels, making the distillers grains unsuitable for some livestock groups.

Identifying corn ear rots can be difficult, especially when multiple diseases are present (Figure 3b) or symptoms are subtle, similar or do not reflect the full extent of infection. If you need help identifying ear rots or other diseases, submit samples to the UNL Plant and Pest Diagnostic Clinic. For mycotoxin analysis, samples should be submitted to a commercial laboratory. Be sure to contact the laboratory for its sampling guidelines or review general guidelines from the Crop Protection Network.

Resources

• Nielsen, R.L. 2012. Premature corn kernel sprouting (aka vivipary). Purdue University. Corny News Network Articles. 
• Rees, J., Cassman, K., Kruger, G., and Glewen, K. 2013. Sprouting corn kernels on hail-damaged ears. University of Nebraska–Lincoln. 
• Paul, P. and Thomison, P. 2018. Premature Sprouting of Corn Kernels. Ohio State University. C.O.R.N. Newsletter.