Decision Time Looming For Fungicide Applications On Corn

Decision Time Looming For Fungicide Applications On Corn

Research determining yield response to fungicide application in corn differs between universities and industry.

Even after two full years of multiple trials, applying fungicides to corn is still not a clear-cut decision for growers. Many growers have experienced yield increases; some have not seen yield increases and some have even seen yield losses from applying fungicides. At a cost of $24 an acre, this is not a decision to take lightly.


Research determining yield response to fungicide application in corn differs between university and industry, but they do agree that yield response is greater when significant disease pressure is present. Iowa State University Extension plant pathologists Alison Robertson and Daren Mueller provide the following observations and recommendations regarding use of foliar fungicides on corn.


What the research shows regarding yield response


Yield responses of hybrid corn to foliar fungicide application vary widely. In Iowa in 2008, the mean yield response in small plot trials was 3.5 bushels per acre in ISU trials conducted by Robertson and colleagues. Similarly, the mean yield response of replicated strip on-farm trials conducted by the Iowa Soybean Association On-Farm Network was 3.5 bu. per acre.


Plant pathologist Greg Shaner at Purdue University compiled data from 13 universities in 2008 across the U.S. and reported a mean yield response of 3.6 bushel per acre. However, an average yield increase of 7.4 bushel per acre was reported by Pioneer Hi-Bred researchers in their evaluation trials across the country and industry has reported 12-16 bu/acre yield increases


While university and industry reports differ in the magnitude of yield responses, one thing both the university and the industry researchers agree on is that yield response is greater when significant disease pressure is present (Table 1). 





Therefore, scouting corn fields prior to an application of a foliar fungicide application can be a worthwhile investment. Fields should be scouted near or at tasseling. A minimum of 100 leaves should be examined per field. At several places within the field, examine the ear leaf and leaves below of several plants to determine if disease is present. If foliar disease is present on the majority of these leaves, a foliar fungicide application may be warranted.


Factors to consider before deciding to apply


Factors that may affect disease development, and thus the decision to apply a fungicide, include hybrid susceptibility to disease, current and predicted weather conditions during grain fill, disease history of the field and previous crop. 


Some basic economics that should be considered before applying fungicides are:
• cost of the fungicide, plus application
• price of corn
• drying costs (corn sprayed with a fungicide often is wetter at harvest)
• harvestability (corn sprayed with a fungicide may have better standability than unsprayed corn)

All these factors affect the economics of a fungicide application.


Other considerations to help you make an informed decision

* Field guides
- Two new resources are available for identifying corn diseases. The most common foliar diseases in Iowa are gray leaf spot, common rust and eyespot.  Other diseases include Northern corn leaf blight and southern rust. A Corn Field Guide (CSI 001), which includes all diseases, insects and disorders, and a pocket card titled 'Scouting for corn diseases' (CSI 0002) are now available from ISU Extension.


* Application timing - One thing ISU Extension plant pathologists have consistently seen over the past few years in several of ISU's on-farm and small plot research treatments is a negative yield response from a portion of the trials.


"While we have not identified any specific reason for these negative responses, one possible cause this past year may have been the uneven crop caused by flooding," says Robertson. "Applications of fungicide prior to tasseling may affect ear development, specifically when an NIS or crop oil is used, according to Purdue and University of Illinois studies in 2008. This season, many fields once again have uneven corn, so if a fungicide is to be applied, we advise waiting until the whole field has tasseled."


* Next year's crop - Lastly, many growers are considering no-till soybeans after corn.  "We have heard reports from the field that residue of corn to which a fungicide has been applied takes longer to breakdown," she says. "This has made planting soybeans in that crop residue difficult the following year."

TAGS: Extension
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