Automatic Tassel (VT) Fungicide Applications in Corn: Should You be Doing One?

I still receive a tremendous number of telephone calls each year regarding automatic fungicide applications to tasseling corn.  As a plant pathologist, I can’t think of a more contentious issue than the use of a fungicide for “plant health” benefits in the absence of disease.  Over the years the jargon regarding this particular fungicide application types and particular timing strategies has changed and now we are conducting research trials at earlier growth stages to determine the potential benefits of vegetative stage (V4 through V7) fungicide applications both alone and with a second application at a reproductive growth stage (VT or R1).

During the 2012 season several fungicide trials were conducted on the experiment station in Stoneville in what could be considered a low disease situation.  Fungicide applications were made at R1 (rather than VT) in 15 gallons of water and all treatments included an adjuvant as a non-ionic surfactant (0.25% v/v).  Plots were rated several weeks after fungicide application and disease levels were judged to be minimal with extremely low levels of northern corn leaf blight, common rust, and southern rust at almost non-existent levels.  In the figure presented, all of the plots that received strobilurin, pre-mix products (as either strobilurin + triazole or strobilurin + carboximide) or triazoles were averaged together by fungicide class to determine how each class responded with regards to yield.  Generally speaking, a limited yield advantage (4.2 bu/A) resulted from strobilurin treatment applications (products included Aproach, Evito, Headline, Quadris).  Economically speaking, depending on the selling price of corn, a 4.2 bu/A response would be somewhere just north of break-even (if somewhere between $5 and $6/bu).  Rates differed for some of the products but generally speaking there were no mathematical differences for either a “normal” rate (as an example, 6 oz of pyraclostrobin) or a higher rate (as an example, 12 oz of pyraclostrobin) (2012 Stoneville corn fungicide trial figure).

Injury associated with an adjuvant that contained nitrogen.

Adjuvants

I want to caution folks if they are planning on making a foliar fungicide application at VT/R1 with any of the fungicide products labeled for application in corn.  Adjuvants are used to increase adherence to plant material as well as allow the product to penetrate the canopy.  Last year in particular there were specific products that were sold under the guise of an adjuvant that contained additional materials such as nitrogen.  Using a product with a foliar fungicide that contains nitrogen can in certain circumstances increase the likelihood of foliar injury following the application.  Keep this in mind prior to making a fungicide application.

Factors to consider before making an automatic fungicide application at VT/R1 include:

-economics (return-on-investment)

-number of years in corn

-irrigation type and/or frequency

-overall yield potential

-presence of a yield-limiting foliar disease

Don’t expect a fungicide application to rescue you from skipping a more important cultural practice.  Use a fungicide for its intended purpose, managing yield reducing foliar diseases.  Reports of a fungicide alleviating drought stress, reducing the likelihood of greensnap (as a result of a vegetative stage fungicide application; see below links) and even increasing the period of grain fill as a result of increased green plant material later in the season have been sporadic and rarely observed in unbiased, university-based foliar fungicide trials conducted in commercial fields or on university experiment stations.

I will leave the decision regarding making an automatic fungicide application up to you, but based on the plots I’ve observed in MS over the past six years, I have not seen a consistent yield and/or economic return as a result of an automatic fungicide application in the absence of observable foliar disease (in well over 40 trials).  One last thought, corn doesn’t require a fungicide to produce yield.  However, a long list of cultural practices are required to corn yield.

Additional information regarding corn responses to early foliar fungicide applications can be found at:

https://www.mississippi-crops.com/2013/04/28/are-early-vegetative-fungicide-applications-beneficial-for-enhanced-corn-production-part-i/

https://www.mississippi-crops.com/2013/04/28/are-early-vegetative-fungicide-applications-beneficial-for-enhanced-corn-production-part-ii-impact-of-fungicide-on-greensnap/

Additional information regarding corn responses to tassel timing foliar fungicide applications can be found at:

https://www.mississippi-crops.com/2011/05/23/the-corn-fungicide-dilemma-when-should-a-fungicide-be-applied-part-i-of-v-yield-in-the-absence-of-measureable-disease/

https://www.mississippi-crops.com/2011/05/26/the-corn-fungicide-dilemma-when-should-a-fungicide-be-applied-part-ii-of-v-irrigated-versus-non-irrigated-situations/

https://www.mississippi-crops.com/2011/05/27/the-corn-fungicide-dilemma-when-should-a-fungicide-be-applied-part-iii-of-v-green-leaf-material-as-measured-by-percent-chlorophyll/

https://www.mississippi-crops.com/2011/05/28/the-corn-fungicide-dilemma-when-should-a-fungicide-be-applied-part-iv-of-v-standabilitylodging/

https://www.mississippi-crops.com/2011/05/29/the-corn-fungicide-dilemma-when-should-a-fungicide-be-applied-part-v-of-v-preventing-yield-loss-from-foliar-disease/