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Hill and Furrow

Scouting in 2014 can inform decisions for 2015 and beyond

Although 2014 variety and hybrid selections were made long ago and foliar fungicide decisions are likely already made because of scouting that took place before tasseling, additional scouting throughout the 2014 growing season can continue to provide important information needed for future growing seasons.

Scouting corn fields again as kernels fill and before physiological maturity may reveal significant disease issues. Perhaps not every hybrid may have been as resistant to leaf diseases as a producer may have liked.  This knowledge can help producers to focus on selecting more resistant hybrids to plant next year. As most of the pathogens that cause corn disease survive over the winter in crop residue, producers scouting fields this year will be also able to pinpoint those fields that are likely to have the highest disease pressure in future growing years. This knowledge can help to inform decisions about whether to consider managing crop residue or rotating to another crop.

Information about hybrid disease susceptibility or resistance is available. Agronomic characteristics and traits such as insect, drought and herbicide tolerance are standard information that seed companies provide to potential customers. In a short period of time I was able to find web-based information from nine companies that market hybrid seed corn in my area.

Information about disease susceptibility or resistance varies significantly among hybrids within a seed company and among companies. Of the nine companies, eight provided information about disease susceptibility or resistance for each hybrid: one company provided ratings for nine different diseases, one for eight diseases, one for seven diseases, two for six diseases, one for five diseases, one for four diseases, and one provided information for only two diseases. Even for those companies that provided information about disease susceptibility or resistance, information was not available for every hybrid and disease combination. All eight companies provided information about susceptibility or resistance to the two foliar diseases that most often cause economic yield loss in Illinois corn: northern corn leaf blight and grey leaf spot.

Caution: take care to not compare apples and oranges. Seven of the eight companies provided a key so that potential customers can easily interpret what is meant by a "4" or a "good" rating for a particular disease in one hybrid to compare that hybrid to another that has a "7" or an "excellent" rating (Figure).

One factor that can complicate the quest to compare disease susceptibility or resistance among hybrids offered by different companies is that different companies have different ratings scales. Of the eight companies that provided disease information, seven provided a ratings scale. The scales from different companies, however, vary widely: one company had a scale that had 10 categories, four companies used scales with nine categories and two companies had scales with five categories.

One might assume that it would be easy to compare hybrid disease susceptibility among those companies that use ratings scales with the same number of categories. Unfortunately this is not the case, as the high or low end of each scale may differ drastically depending upon how each company defines its ratings scale. As an example, one need only look at the ratings scales with nine categories. A hybrid with a score of "9" can have "poor" level of disease resistance with one company and an "excellent" level of disease resistance with another company. This is why it is often much easier to compare hybrids within a company than to compare hybrids between different companies.

Further information.

Foliar fungicides. If foliar fungicides decisions have not yet been made, check out this great article from Iowa State University Extension that provides advice about how best to prioritize scouting time and decisions AND the Corn Foliar Disease: Identification and Management Guide which can help distinguish diseases cause by fungi and bacteria.

Hybrid disease resistance/susceptibility. It may be worthwhile to call local/regional seed salespeople to more quickly gather the disease susceptibility/resistance information.