Effect Of Strobilurin Fungicides Applied At Two Timings On Seed Yield in Tall Fescue.

Stem rust is frequently a serious problem in tall fescue seed crops in Oregon’s Willamette Valley. Under severe rust pressure, seed yields can be reduced over 70% when rust is not controlled however adequate stem rust control can be obtained with currently available fungicide materials. The newer class of strobilurin fungicides has been reported to provide a yield boost beyond that from disease control in some crops. Although a significant production expense, many Willamette Valley grass seed producers have begun integrating an early application of a strobilurin fungicide at BBCH growth stage 32-33, prior to the typical onset of stem rust in the crop. This study was conducted to determine if and under what circumstances this early strobilurin fungicide treatment increases tall fescue seed yield compared to a standard fungicide treatment applied when stem rust begins to develop.  Results were obtained from large scale, on-farm yield trials conducted on five turf-type tall fescue seed fields from 2010 – 2012. Seed yield and weight and flag leaf N concentration were measured. Treatments included 1) control, 2) 10 oz/a axoystrobin + propiconazole applied at BBCH 32-33, 3) 12 oz/a axoystrobin + propiconazole applied at BBCH 59, and 4) 10 oz/a axoystrobin + propiconazole applied at BBCH 32-33 plus 12 oz/a applied at BBCH 59. Strobilurin fungicide treatments increased tall fescue seed yield by an average of 17% over the untreated control over the untreated control across sites and years. Applying the strobilurin fungicide early increased seed yield by 52% in 2012 when stem rust pressure was severe and 7% in 2010 and 2011 when stem rust pressure was minimal.  The increase in seed yield due to strobilurin fungicide treatments was attributed to increased seed weight. Nitrogen tissue concentrations were not influenced by fungicide treatments. The results of this study suggest that early strobilurin fungicide application is beneficial in tall fescue seed crops in years of severe rust pressure.