The corn fungicide dilemma: when should a fungicide be applied? Part II of V, irrigated versus non-irrigated situations

Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist May 26, 2011 22:45

The corn fungicide dilemma: when should a fungicide be applied? Part II of V, irrigated versus non-irrigated situations

From 2007 through 2009 Mississippi State University extension and research personnel were involved in a large corn fungicide research effort funded by the Mississippi Corn Promotion Board.  Except for situations where corn was planted on experiment stations (Brooksville, Pontotoc, Raymond, Starkville, and Verona) corn fields were randomly chosen throughout the Delta and were either furrow irrigated (14 locations) or pivot irrigated (one block of one location in 2007).  The other 12 locations included in the study were planted in plot-type situations, with rows generally longer than 100 feet, on experiment stations in non-irrigated environments. 

Over the past few seasons fungicide applications, specifically those containing a strobilurin fungicide (the QoI, or quinine-outside inhibitor fungicides) and almost exclusively Headline or Quadris, have been suggested as a means of reducing the likelihood of drought stress.  More often than not this is referred to as “increased water use efficiency” by the plant following the fungicide application.  Little if any hard data exists throughout the corn producing states from land grant universities with regards to whether or not this particular practice is beneficial (i.e. benefits yield).  However, by considering the data from non-irrigated plot locations in MS and comparing yields between fungicide treated (Headline, Propimax, Quilt) and untreated plots one can make a statement regarding the performance of a fungicide in a “drought-like” situation with regards to water use efficiency by considering the overall harvested yield.  Both 2007 and 2008 were atypically dry years throughout the corn growing season (March – early September).  Although the fall of 2009 was a wet part of the year, the majority of the season was reasonably dry. 

Again, as in the first part of this series, fungicides were applied at tassel (VT) and included crop oil concentrate at a rate of 1.0% v/v in 5 gallons of water by air and suggested water volumes for ground application.  Foliar diseases were rated in addition to ratings that were conducted after plants were destructively sampled from trial plots.  Plots were harvested at physiological maturity.     

The data presented in the two figures are the same as the set presented in Part I; however, irrigated (Figure 1) and non-irrigated (Figure 2) situations were separated to present potential yield differences between treated and untreated plots.  Yield from non-irrigated plots was substantially less than those from irrigated locations.  Moreover, as I have presented in the past there were little or no mathematical differences between treated and untreated plots, no statistically significant differences, and applying a fungicide was not deemed to produce an economic benefit (based on the average of all locations).  As I stated in Part I, essentially there was a relative absence of foliar disease regardless of year or location.  Regardless of irrigation, fungicides were not beneficial and applications did not result in a yield increase in either situation.  If a fungicide application had resulted in greater water use efficiency the resulting yield would have likely been greater than the untreated plots.

Part III will present data regarding chlolorphyll readings between treated and untreated plots.

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Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist May 26, 2011 22:45
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