Simply finding northern corn leaf blight lesions or lesions caused by another disease is not a good enough reason to apply a fungicide to your corn fields, says Tom Allen, Mississippi Extension plant pathologist.

As he’s scouted Delta corn fields in recent weeks, Allen has identified two diseases — northern corn leaf blight and Holcus spot — “with regularity.”

Suggestions that farmers should be making blanket fungicide applications when NCLB is detected are wrong, Allen noted in the most recent issue of the Mississippi Crop Situation. “Corn should be scouted and a fungicide applied in response to a yield-limiting disease situation.… A blanket fungicide application at tassel in the absence of foliar disease is not economical,” he said.

Agronomic considerations Allen says should be a part of a fungicide decision include:

• Row spacing

• Irrigation type

• Hybrid susceptibility

• Growth stage

• Number of lesions present and placement in the crop canopy

• Yield potential

• Number of years in continuous corn production

“In addition, depending upon disease pressure and weather conditions, a fungicide application will only provide 21 to 28 days of disease prevention — depending on the labeled rate,” Allen said. “In no way will a fungicide application provide protection until harvest if applied today.”

Bottom line: “The necessity to apply a fungicide should be made on a field-by-field basis.”

To read Allen’s discussion of Holcus leaf spot and northern corn leaf blight in Mississippi Delta corn, download a copy of the latest Mississippi Crop Situation.