CORN Newsletter: 2006-32, September 26, 2006

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C.O.R.N Newsletter 2006-32
September 26, 2006 - October 2, 2006

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Corn Stalk Rot: A Disease Caused by Several Different Fungi
by Pierce Paul, Peter Thomison, Dennis Mills


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Corn stalk rot and lodging are the results of several different but interrelated problems. The actual disease, stalk rot, is caused by one or more of several fungi capable of colonizing and disintegrating of the inner tissues of the stalk. The most common members of the stalk rot complex are Gibberella zeae, Colletorichum graminicola, Stenocarpella maydis and members of the genus Fusarium.

The extent to which these fungi infect and cause stalk rot depends on the health of the plant. In general, severely stressed plants (due to foliar diseases, insects, or drought) are more greatly affected by stalk rot than stress-free plants. The stalk rot fungi typically survive in corn residue on the soil surface and invade the base of the corn stalk either directly or through wounds made by corn borers, hail, or mechanical injury. Occasionally, fungal invasion occurs at nodes above ground or behind the leaf sheath. The plant tissue is usually resistant to fungal colonization up to silking, after which the fungus spreads from the roots to the stalks. Following infection and colonization, leaves turn grayish-green in color, ears droop, the lower part of the stalk turns from dark green to light brown, and the pith inside the stalk becomes soft. When diseased stalks are split, the pith is usually discolored and shows signs of disintegration. As the pith disintegrates, it separates from the rind and the stalk becomes a hollow tube-like structure. Destruction of the internal stalk tissue by fungi predisposes the plant to lodging.

Based on our observations and reports coming in from across the state, stalk rot and lodging seem to be the main causes for concern as growers prepare for harvest. Although the level of stalk rot generally varies from location to location, the problem seems to be more widespread this year; with huge sections of some fields having almost every plant showing stalk rot symptoms. This is largely because many areas of the state experienced an extended period of dry weather during the grain fill period (July and August). Please refer to a recent C.O.R.N Newsletter article by Thomison and Paul for more on drought-related stresses and stalk rots (“Potential for Stalk Rot and Lodging Problems in Corn”) available at:
http://corn.osu.edu/story.php?setissueID=153&storyID=919

Nothing can be done about stalk rots at this stage; however, growers can minimize yield losses associated with lodging by harvesting fields with stalk rot problems early. Scout fields early for visual symptoms of stalk rot and test stalk integrity by squeezing the lower internodes between the thumb and forefinger. Stalks that are likely to lodge are easily compressed between the fingers. Since the level of stalk rot varies from field to field (being more severe when corn follows corn) and hybrids vary in their stalk strength and susceptibility to stalk rot, each field should be scouted separately. For more information on the different type of stalk rot and stalk rot management please refer to the OSU Plant Pathology web site "Ohio Field Crop Diseases" at:
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/

Readers can subscribe electronically to this newsletter by signing up at http://agcrops.osu.edu/services/email.html. E-mail labarge.1@osu.edu if you have problems subscribing or no longer wish to receive this newsletter.

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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