The corn fungicide dilemma: when should a fungicide be applied? Part III of V, green leaf material as measured by percent chlorophyll

Since 2007, fungicide products containing a strobilurin active ingredient have been suggested to increase plant “greenness” or allow the plants to stay greener longer in the field following a tassel (VT) application.  Increased green plant tissue has been stated to be a benefit to producers since plants that stay greener longer may result in an increase in yield or allow the plants to remain in the field longer thus preventing a harvest bottleneck.  As a portion of the research project conducted by MSU and funded by the Mississippi Corn Promotion Board, percent chlorophyll was measured using a SPAD meter.  Fields were rated approximately 14-21 days post-application.  Thirty ear leaves were randomly chosen while rating plots for the presence of foliar disease.  The SPAD meter was gripped to the leaf and the reading recorded.  After rating plots the data was averaged by the SPAD meter and recorded as a plot average of the 30 leaf sample.  Briefly, a SPAD meter measures plant tissue greenness as the reflectance of plant chlorophyll and accounts for N status.  Data are returned as a percentage of N and chlorophyll.  Plants that have sufficient nitrogen achieve maximum greenness while plants that are N-stressed will not be as green. 

Data contained within the above table are from the same locations contained in Parts I and II.  The only difference has to do with the number of locations.  Two locations were not harvested during 2009 due to severe lodging that occurred following straight-line wind events (this will be the topic covered in Part IV).  Measurement averages are presented by treatment, year, and average of all treatments over all years (gray column on far right).  SPAD readings, recorded during 2007 to 2009, were not significantly different between treated or untreated plots or specific products for year or regardless of year.  Moreover, while there were subtle mathematical differences between treated and untreated plots, treatment with a strobilurin or strobilurin + triazole mix did not greatly enhance chlorophyll or green plant tissue post-application.