Vegetative Stage Corn Fungicide Applications in the Mississippi Production System: 2013 Large Plot Trials

Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist March 17, 2014 08:05

Over the past several years a shift in the suggested fungicide application timing has moved from more common application timings, such as tassel (VT/R1), to vegetative stage applications between V4 and V7.  Depending on where you are geographically in the United States the fungicide rates associated with the suggested vegetative timings range from full application rates (e.g., 4 oz of Stratego YLD) or a “half-rate” (e.g., 2 oz of Stratego YLD).  However, in some cases the “half-rate” is considered to be more of a “full rate” at this timing because the plants are not yet full size.

Trials have been conducted in Mississippi for the past two seasons as a portion of a Mississippi Corn Promotion Board project to determine the specific benefit of vegetative fungicide applications.  Most of the trials have been conducted in small plot fashion in Stoneville and a location outside of Greenwood.  However, last year additional locations were added in east MS to consider the benefit of a vegetative fungicide application in two large plot trials conducted with the help of Dennis Reginelli.  A single fungicide, Quilt Xcel, was applied at 10.5 fl oz/A at V6 in a pivot irrigated and a non-irrigated field situation.  The fungicide-treated strips were replicated three times in addition to nontreated strips.  Trials were rated for the presence of disease late in the season (approximately dent – R5).  Foliar diseases that would be considered to be present in continuous corn situations such as gray leaf spot, northern corn leaf blight, southern corn leaf blight, were not present to any substantial, yield-limiting level in either of the two fields.  However, southern corn rust was present at substantial levels in the irrigated field.  At this late growth stage a second fungicide application was not suggested.

Trials were harvested at the end of the season and yield calculated from the two locations to determine if there were differences between treated and nontreated plots.  At the non-irrigated location the fungicide treated plots yield 2.7% lower than the nontreated plots (199.1 bu/A nontreated vs. 193.7 bu/A treated).  In addition, minimal differences existed between the treated and nontreated in the irrigated field.  A 0.4 bu/A positive response resulted from the fungicide (215.2 bu/A treated versus 214.8 bu/A nontreated).  See 2013 large plot corn trials for the graphic presentation of these data.

Several key points to keep in mind when deciding on a vegetative fungicide application in corn:

1)     Between V4 and V7, regardless of hybrid, few if any foliar disease is present.  Therefore a fungicide will likely not be a beneficial measure from a disease management standpoint.

2)     Fungicides applied at vegetative timings will not provide season long disease prevention.

3)     Several additional claims have been made regarding the effect of vegetative fungicide applications (e.g., enhanced root growth, reduced need for irrigation, increased nutrient uptake, and a general increase in yield).  Additional trials from unbiased sources are necessary to determine the overall impact of vegetative fungicide applications.

4)     If you are planning on trying a vegetative fungicide application, leave a nontreated strip for comparison to see if the application was in fact beneficial.

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Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist March 17, 2014 08:05
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