Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu
Over the course of the week many people have asked if or when fungicide use is profitable in the 2014 corn crop. Unfortunately the answer is not straightforward. The answer depends on several factors including 1) potential for disease (hybrid, environment, and disease), 2) grain price, 3) yield potential and 4) the cost of fungicide application.
Potential for disease. The first thing you need to do when determining if/when you should apply a fungicide to corn this year is determine how much disease there is in the field. The most common disease in the area this year is Grey leaf spot. The hot temperatures have not been favorable for Northern Corn Leaf Blight and rusts typically are not a major concern. See my update from earlier in this issue of the WCU regarding field corn diseases. If you have greater than 5% severity on any of the three leaves below the ear in 50% or more plants in the field then the level of disease might require intervention. However, other factors will impact future development of disease including hybrid genetics and the environment. A “worst case environmental scenario” for a residue born disease such as Grey leaf spot is a no-till, irrigated field of continuous corn with a history of the disease. Table 1 provides some guidelines that may help you determine the risk level of your field and if a fungicide may potentially benefit your crop.
Table 1. Level of fungicide need for protecting corn yield from Grey leaf spot. In this table disease is assumed to be present on 50% or more of plants at greater than 5% severity on the 3rd leaf below the ear leaf or above. In addition, the worst case scenario is assumed: a field with a history of GLS, no-till, corn after corn, and moderate temperatures. The lack of any of these factors will further reduce the likelihood of a fungicide benefitting the crop.
Potential for fungicide benefit to cover application cost. With corn heading towards $4.00 per bushel, a greater yield benefit is needed to cover costs. Table 2 provides examples of the bushel returns you would need to cover fungicide treatment (applicator cost + product) at different grain prices.
Table 2. The required bushel/acre yield increases required to pay for various fungicide application costs at 5 different grain prices.
The likelihood that a fungicide will pay for itself is greatest in situations where disease potential is high, application costs are low, and grain prices are high. How often does the fungicide pay for itself? A 2011 paper published in the journal Phytopathology examined 187 studies of corn responses to fungicides conducted throughout the Corn Belt from 2002-2009. The chance that the application costs of a fungicide would be covered by the yield return were estimated across a range of grain prices ($2-$7 per bu) and application costs ($16-$40 per acre). In a nutshell, the research showed that in over 85% of the grain/application cost combinations, there was a greater than 50% chance that the application of a fungicide would not pay for itself if there was less than 5% disease severity on the ear leaf between R4 and R6. Conversely, only 33% of the grain/application cost applications did not pay when there was more than 5% disease severity on the ear leaf between R4 and R6. The study showed that although fungicide use in corn can certainly be beneficial, responses are also highly variable from location to location and year to year. For example, fungicide applications reduced corn yields in 26-48% of the studies included in the metaanalysis. The take home message is that you will need a greater bu/A yield increase this year to cover the application cost. You are more likely to recover this cost in disease favorable environments (no till, irrigated, corn after corn, history of GLS) when susceptible hybrids are planted. As with most things in agriculture, nothing is guaranteed.
Reference: P. A. Paul, L. V. Madden, C. A. Bradley, A. E. Robertson, G. P. Munkvold, G. Shaner, K. A. Wise, D. K. Malvick, T. W. Allen, A. Grybauskas, P. Vincelli, and P. Esker. 2011. Meta-Analysis of Yield Response of Hybrid Field Corn to Foliar Fungicides in the U.S. Corn Belt. Phytopathology 101:1122-1132.