Over the course of the week many people have asked if fungicides will be profitable in the 2014 corn crop. The answer depends on several factors including: 1) potential for disease (hybrid resistance level, environment, presence or history of disease), and 2) economics (grain price, yield potential, and the cost of fungicide application). I’ll try to keep the discussion as to the point as possible for clarity.
Potential for disease. The first thing you need to do when deciding if/when you should apply a fungicide to corn this year is to determine how much disease there is in the field. The most common disease in Delaware this year is Grey leaf spot. For Grey leaf spot and other residue-borne 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-borne 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 based on hybrid resistance rating and irrigation practice.
Table 1. Hybrid resistance rating to Grey leaf spot, irrigation, and potential need for fungicide application in Delaware. 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 benefiting the crop.
|Hybrid Resistance Rating to GLS
||Potential need for fungicide application (VT-R2)
*In general, dryland corn that is highly resistant to GLS does not require a fungicide application for management.
Economics. With corn heading towards $4.00 per bushel, a greater yield benefit is needed to cover application 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.
|Application Cost (per Acre)
||Grain Price (bu)
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 chances that the application costs of a fungicide would be covered by the yield return were estimated across a range of grain prices ($2-7 / bu) and application costs ($16-40 / 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 combinations did not pay when there was more than 5% disease severity on the ear leaf between R4 and R6. Therefore, the greatest chance for a grower to break even or profit from a fungicide is when the potential for disease is high.
In addition, 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 or other common residue-borne diseases) when susceptible hybrids are planted.
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.