Corn Ear Rots and Kernel Molds

Ear rot diseases have molds that can be associated with kernel injury from insects, hail, frost, or birds. Also, drought and heat stress during the growing season, especially during pollination and as kernels mature, encourage the development of some ear molds. Several ear rot diseases can produce mycotoxins, which are fungal metabolites that are toxic when consumed by animals or humans. Proper grain drying and storage techniques should be used when handling corn with a high frequency of kernel molds.

Many pathogens that cause stalk rots may also initiate ear rots. These fungi can remain viable in the soil for several years. Fields with a history of ear rots and stalk rots should be scouted, even if practices have been implemented to decrease disease pressure. Some management options that may reduce the risk of ear mold infection include selecting seed products with ear rot and stalk rot resistance and insect protection traits, crop rotation (especially under reduced tillage environments), and balanced soil fertility.

Not all corn ear molds produce mycotoxins and not all fungi capable of producing toxins do so. It is helpful to be able to identify corn ear molds in order to manage grain that may have the potential to produce mycotoxins.

Figure 1

Figure 1. Aspergillus (left) and Penicillium (right) ear rots

Aspergillus Ear Rot (Figure 1, left). Characterized by a tan, sooty-black, greenish, or greenish-yellow mold that usually starts at the ear tip. Infection often follows hot, droughty growing conditions and insect feeding on kernels. Mycotoxins such as aflatoxin are produced.

Penicillium Ear Rot (Figure 1, right). Evident as tufts or clumps of a blue-green or gray-green mold “erupting” through the pericarp of individual kernels.

Figure 2

Figure 2. Fusarium ear rot

Fusarium Ear Rot (Figure 2). Infected kernels have a white-to-pink cottony mold which are scattered around the ear. Infected kernels have white streaks that are arranged in a starburst pattern. The mold can produce fumonisins, which is a mycotoxin.

Figure 3

Figure 3. Diplodia ear rot

Diplodia Ear Rot (Figure 3). Dry weather early in the season followed by abnormally wet weather just before and after silking, favor infection. Symptoms include prematurely bleached or straw-colored ear leaf and husk. Dense white to grayish-white mold will be matted between the kernels and between the ear and husk.

Figure 4

Figure 4. Gibberella ear rot

Gibberella Ear Rot (Figure 4). Identified by having white to pinkish to reddish mold that starts at the tip of the ear and progresses towards the base of the ear. More common in seasons with cool, wet, weather from silking to harvest. Capable of producing the mycotoxins: vomitoxin and zearalenone.

To minimize ear mold growth and mycotoxin production in storage, consider the following recommendations:

  • Harvest drought-stricken and insect infested grain at early maturity as soon as moisture content allows minimum damage.
  • Adjust the combine header speed to minimize cracking and reduce the content of trash, fines, and small broken or mold-infected kernels. Nearly 50 percent reduction in aflaltoxin levels (Aspergillus ear rot) can be achieved in some situations by monitoring combine cylinder, screen, and air flow levels.
  • Dry all grain to at least 13 to 14 percent moisture as soon as possible, not to exceed a 24 to 48 hour period after harvest, which helps prevent the production of aflatoxins. Safe, long term storage (nine months or more) may be achieved at a uniform moisture level of 13 percent.
  • Cool grain after drying and maintain dry storage conditions. If possible, cool grain down to 35 to 40ºF.
  • Thoroughly screen and clean the grain before storage to remove dust, crop debris, and cracked or broken kernels. A large portion of the contamination is in the small, broken kernels.

Continue periodic aeration and probing for “hot spots” at one to four week intervals throughout the storage period.