CORN Newsletter: 2009-35, October 12, 2009

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C.O.R.N Newsletter 2009-35
October 12, 2009 - October 20, 2009

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Corn Ear Rot: Which One is It?
by Pierce Paul, Dennis Mills


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Several different types of ear rot problems are showing up in some of Ohio’s corn fields this year, and lots of questions are being asked about these problems and how to tell them apart. Reported symptoms range from those typical of common ear rots to relatively uncommon symptoms such as blackish mold growth on the ear. It is important to identify ear rot problems before harvest because some ear rot fungi produce mycotoxins that are harmful to livestock.

Good indicators of potential ear rot problems are:

1. Wet weather conditions late in the season
2. Frost occurring before maturity
3. Corn standing in the field for an extended period in late fall
4. Delayed maturity (dry-down)
5. Bird and insect damage
6. Hybrid susceptibility
7. Ear drying-down in an upright position.

Generally, it is fairly easy to tell ear rots apart based on the color of the fungal growth on the ear, how the mold develops, and how the moldy kernels are distributed on the ear. The three most common ear rots in Ohio are Gibberella, Diplodia and Fusarium ear rot. Gibberella ear rot, is the most prevalent of the ear rots this year, however, we have also received reports of Diplodia ear rot in some fields. With Gibberella ear rot, the fungus enters the ear tips through the silk channel. A pinkish mold starting at the tip and progressing toward the base of the ear is very typical of this disease. Gibberella ear rot develops best when cool temperatures and frequent rainfall occur during the 3-week period after silk emergence. Hybrids that dry-down with the ear in a declined position are less likely to have problems with Gibberella and other ear rots.

Like Gibberella ear rot, Fusarium ear rot also causes pinkish discoloration of infected kernels, the fungus also enters through the silk, and the disease develops best when warm, wet weather occurs during the 2 to 3 weeks period after silking. However, with Fusarium ear rot, the pink moldy kernels are usually scatters all over the ear. As the disease develops, the infected kernels may become tan or brown or have white streaks. Ears that dry-down in declined position and those free of injuries and well covered with husks are less prone to Fusarium ear rot.

Diplodia on the other hand causes a thick white mold to grow on the ear, usually starting from the base and progressing toward the tip. Infection can begin before tassel emergence up to silking, and disease development is favored by wet weather and mild temperatures during early ear development. As the disease develops, the entire husk becomes bleached, covered with whitish-gray mold, and glued to the kernels. Infected ears are usually lightweight and may become rotten. Hybrids that dry-down with the ear in an upright position are more prone to Diplodia ear rot because the fungus can penetrate the husk through the base of the ear.

Symptoms of ear rot do not always appear on the outside of the husk. This is particularly true with late infections. So, to determine if you have an ear rot problem, walk fields, strip back the husks of about 50 plants spread out across the field and look for the following telltale symptoms:

Gibberella ear rot:
* Pinkish mold starting at the tip and progressing toward the base of the ear.

Fusarium ear rot:
* Pinkish or tan moldy kernels scattered on the ear.

Diplodia ear rot:
* White mold growth starting at the base and moving up the ear
* Husk glued to kernels
* Lightweight ears

Other important, but less common ear rots:
* Aspergillus ear rot: Yellowish-green to dark green powdery mold on the ear that typically develops under hot, dry conditions. This ear rot may lead to aflatoxin contamination of grain.
* Cladosporium ear rot: Dark, greenish-black streaks scattered over the ear. This ear rot is often associated with insect, hail or frost damage.

For more on ear rots and mycotoxins visit:
http://corn.osu.edu/story.php?setissueID=324&storyID=1927
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm
http://www.ipm.iastate.edu/ipm/icm/2002/10-21-2002/molds.html

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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