Diplodia and Other Ear Rots in Central and Northern Illinois

Diplodia ear rot is being found in Central and Northern Illinois fields. Other ear rots may also occur depending on favorable environmental conditions and kernel damage. Favorable environmental conditions vary by mold but can include excessive moisture, drought, and heat stress during the growing season, especially during pollination and as kernels mature. Insects, birds, hail, or early frost can damage kernels and result in mold growth. 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.

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Figure 1

Figure 1. Ear Rots: Diplodia from ear base and from tip down (top), Aspergillus (bottom left), and Penicillium (bottom right).

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Diplodia Ear Rot (Figure 1, top). Development is favored by early-season dry weather followed by abnormally wet weather just before and after silking. 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. The disease usually infects from base of ears to the top, but can also infect from the tip down.

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

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Penicillium Ear Rot (Figure 1, bottom right). Favored by insect injury to kernels. Tufts or clumps of a blue-green or gray-green mold protrude through the pericarp of individual kernels.

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Figure 2

Figure 2. Fusarium ear rot

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Fusarium Ear Rot (Figure 2). Favored by hot, dry weather after flowering and minimum tillage. 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.

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Gibberella Ear Rot (Figure 3). More common in seasons with cool, wet, weather from silking to harvest. 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. Capable of producing the mycotoxins vomitoxin and zearalenone.

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Figure 3

Figure 3. Gibberella ear rot

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

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  • Harvest drought-stricken and insect infested grain at early maturity as soon as moisture content allows minimum damage.
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  • 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.
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  • Dry all grain to at least 13 to 14 percent moisture content 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 content level of 13 percent.
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  • Cool grain after drying and maintain dry storage conditions. If possible, cool grain down to 35 to 40 ºF.
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  • 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.
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Continue periodic aeration and probing for “hot spots�? at one to four week intervals throughout the storage period.