When considering the use of a fungicide in corn or soybean, growers should take into consideration what the anticipated return could be from the fungicide application. In some instances, the return can be measured directly in an increase in yield (bushels/acre) and/or seed quality. In other instances, the return from the application may be indirectly measured in the form of improvement in the health, standability and harvestability of the crop. These indirect benefits may not measure in bushels or dollars; however, they may result in increased efficiency, harvestability and peace of mind.
A grower should calculate where he may expect to see the greatest returns by evaluating factors that influence the response of a crop to fungicides. Factors to consider include:
Corn and soybean products that are more susceptible to foliar diseases generally exhibit a greater response to a fungicide than those with high or moderate resistance to foliar diseases. Hot, humid weather favors many foliar diseases including gray leaf spot in corn (Figure 1) and frogeye leafspot in soybean (Figure 2). Warm, wet weather tends to favor northern corn leaf blight in corn and the Diaporthe complex in soybean. Dry weather tends to slow or stop the development of most pathogens. Fields with a history of foliar disease or fields with high amounts of residue are at greater risk because disease pathogens can survive on crop residue. Finally, consider the timing of the application relative to the growth stage of the crop to gauge an anticipated response. Studies have shown optimal timing for yield increase to be near VT stage in corn or R3 stage in soybean.1,2
1Hershman, D.E., Vincelli, P., and Kaiser, C.A. 2011. Foliar fungicide use in corn and soybean. University of Kentucky. PPFS-GEN-12.
2Bohner, H. 2014. What is the correct time to apply foliar fungicides to soybeans? Crop Talk. www.omafra.gov.on.ca.
Foliar fungicide use in corn and soybean. Agronomy ADVICE. Channel.com. https://www.channel.com/agronomics/Documents/AgronomicContentPDF/Foliar%20Fungicide%20Use%20in%20Corn%20and%20Soybean%20-%20Channel.pdf
Multiyear foliar fungicide study on soybeans. Agronomy ADVICE. Channel.com. http://www.channel.com/agronomics/Documents/AgronomicContentPDF/Multiyear%20Foliar%20Fungicide%20Study%20on%20Soybeans%20-%20Channel.pdf