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Agronomic Crops > Crops Blog > Posts > Yield response and target spot control on selected cotton varieties with fungicides

A study was conducted at the Gulf Coast Research and Extension Center to assess the control of target spot and yield response of susceptible and partially resistant cotton varieties as influenced by applications of recommended fungicides.  A factorial set of treatments was arranged in a split-split plot with year as the whole plot, cotton variety resistance as the split plot and fungicide program as the split-split plot.  While the partially resistant varieties Deltapine 1050 B2RF, Deltapine 1252 B2RF, and Deltapine 1137 B2RF were produced in 2012, 2013, and 2016, respectively, the target spot susceptible variety PhytoGen 499 WRF was sown in all three study years.  Fungicide programs consisted of two applications of Headline 2.09SC at 6 and 9 fl oz/A, Quadris 2.08SC at 6 and 9 fl oz/A, or Twinline at 7 and 8.5 fl oz/A along with a non-treated control.  Applications, which were scheduled at the 1st and 3rd week of bloom in 2012 and 2013, were delayed until the 3rd and 5th week of bloom in 2016.  In all study years, final % defoliation was greater for PhytoGen 499 WRF than any of the Deltapine varieties.  For PhytoGen 499 WRF, the highest final defoliation of 71% occurred in 2012, while a low of 47% defoliation was recorded in 2013.  When compared with Deltapine 1050 B2RF at 34% defoliation in 2012, 25% and 21% defoliation was noted for Deltapine 1252 B2RF and Deltapine 1137 B2RF in 2013 and 2016, respectively.  Over the three-year study period, lower final % defoliation was observed for the Headline, Quadris, and Twinline-treated cotton than the non- treated control with the 9 fl oz/A rate of Headline proving more effective than both rates of Quadris in controlling target spot.  Application rate did not influence disease control with Headline, Quadris, or Twinline.  Significant year × variety and variety × fungicide program interactions for seed yield were noted.  While the 3239 and 2869 lb/A seed yield for PhytoGen 499 WRF was similar to Deltapine 1050 B2RF at 3321 lb/A and Deltapine 1137 B2RF at 2975 lb/A in 2012 and 2016, respectively, Deltapine 1252 B2RF had a higher seed yields of 3195 lb/A than PhytoGen 499 WRF at 3001 lb/A in 2013.  Seed yield for PhytoGen 499 WRF as well as the three Deltapine varieties differed by study year.  For the Deltapine varieties, similar seed yields  were noted across all fungicide programs including the non-treated control.  With PhytoGen 499 WRF, significant seed yield gains were recorded with all fungicide treatments except for the 6 fl oz/A rate of Quadris compared with the non-treated control.  Also, PhytoGen 499 WRF seed cotton yields were greater for both rates of Twinline than the 6 fl oz rate of Quadris.


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