If you've decided you should apply a fungicide on corn, which one should you apply? Kiersten Wise, Purdue University Extension disease control specialist, has prepared BP-760-W, a simple handout that lets you compare how various products perform against certain corn diseases. Then you can determine which product best fits your needs.

It's called an efficacy chart. It was developed by a group called the Corn Disease Working Group. The group determined ratings for each fungicide by field-testing the materials over multiple locations and multiple years.

The ratings are based on disease control, she notes. They do not necessarily reflect the ability of the product to boost corn yield.

Know the symptom: Your first reaction might be that this is a fungal disease. But his is actually nitrogen deficiency. A fungicide would not help the primary problem.

Efficacy is not just how good the product is on a disease, Wise says. Efficacy also depends upon proper application timing, application method as prescribed by the level and overall amount of disease pressure in the field.

Wise hopes the idea of having and efficacy chart will cause farmers to do two things. First, they need to realize there are different modes of action of fungicides. At this time there are no known pathogens resistant to a corn fungicide. But she believes it's important to use varying modes of action to prevent resistance from developing in the future. The efficacy table also lists restrictions for use for each product. Some can be applied much closer to harvest than others, for example.

To use the chart, if you know your hybrid is susceptible to gray leaf spot, you find lesions in the field and the near-term weather forecast indicates conditions will be favorable for that disease, then you want to prepare a treatment option for gray leaf spot in that field. Since gray leaf spot in your target, look for materials that are as effective as possible against gray leaf spot, and which still fall within your use restriction and application guidelines.

To learn more, call 1-888-EXT-INFO or visit www.extension.purdue.edu.