Heat, Stress and Disease Affecting Iowa Corn

Heat, Stress and Disease Affecting Iowa Corn

This year the bacterial disease Goss's wilt was identified in Iowa much earlier than in previous years. If your cornfields haven't had this disease before, should you be worried? What about feeding this corn to livestock?

This year the bacterial disease Goss's wilt was identified in Iowa much earlier than in previous years. That is prompting some concern among corn growers whose fields previously had not been affected by this disease. Should you be worried if your fields haven't had this disease before? What about livestock producers—should they be concerned about feeding corn grain, or stalks or silage from fields that have Goss's wilt?

"Since its initial identification in cornfields in the U.S. more than 40 years ago, Goss's wilt hasn't been a serious problem for farmers growing corn in most Iowa locations," says Alison Robertson, an Iowa State University Extension plant pathologist. "In the past few years, however, the disease has become more common. This year it did show up in the state much earlier than in previous years, causing some concern, especailly among farmers whose fields haven't been affected by Goss's wilt before."

Goss's wilt is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis (Cmn), which enters the plant through wounds that can be caused by rain, wind, hail or insect damage. Drought-stressed plants may be more susceptible to such wounds, and subsequent bacterial infection. But Steve Ensley, of Iowa State University's Veterinary Diagnostic and Production Animal Medicine department, says drought stress presents a much bigger potential problem than Goss's wilt for livestock producers.

Drought stress is bigger potential problem than Goss's wilt for livestock

"Nitrate concentration or cyanide concentration in drought-stressed corn can be a serious threat to livestock use," Ensley says. "Nitrate is converted to nitrite in the rumen, and nitrite converts blood hemoglobin to methemoglobin, which cannot transport oxygen to body tissues. Cyanide concentration, also known as prussic acid poisoning, works in a similar manner. In both cases, animals often die because of lack of oxygen."

ISU scientists and others say there are no reported issues with feeding corn grain, stalks or silage that comes from fields infected by Goss's wilt, to cattle. And, there is no scientific evidence supporting harm to cattle caused by this bacterium.

Because the Goss's wilt bacteria can overwinter in crop residue for several months, continuous corn acres and low-till or no-till fields are at higher risk for developing Goss's wilt. ISU's Robertson says there are steps farmers can take to reduce the survival rate of the responsible bacterium in future years.

"Research has shown that pure soil cultures generally survive less than two weeks. However, bacteria found on surface crop residue can survive for 10 months," she says. "Some conservation tillage methods, including partially burying infected residue, should reduce the survival rates. However, soil conservation measures should always be considered. Also, heat, competition with other microbes and low pH reduce the survivability of the bacterium."

Websites offer information on mycotoxins and feeding corn

Nitrate Toxicity by Nolan Hartwig, ISU Extension Veterinarian (2005)

Reduce Risk of Mycotoxin Contamination by Scouting Fields for Ear Rot by Alison Robertson, Department of Plant Pathology and Microbiology; and Charles Hurburgh, Iowa Grain Quality Initiative (2011)

Goss's Bacterial Wilt and Leaf Blight by Tamra Jackson, University of Nebraska—Lincoln

Potential for High Nitrate Levels in Drought-Stressed Corn Silage by Ron Heininger and Jim Dunphy, North Carolina Extension

Preventing Nitrate Problems in Drought-Damaged Corn by S.D. Livingston, C.D. Coffman and J.C. Paschal, Texas A&M University Extension

An additional contact: Steve Ensley, ISU Veterinary Diagnostic and Production Animal Medicine, 515-294-1950, [email protected]
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