Foliar Fungicide Evaluation At Different Growth Stages in Hard Red Winter Wheat.

A 3-year experiment was conducted near College Station, TX in the Brazos River Bottom to evaluate the effect of fungicide timing on four different wheat varieties (Triticum aestivum L.).  The four varieties used in this experiment represented a range of host plant resistance levels to leaf rust (Puccinia triticina) including: resistant (cv. Fannin), moderately resistant (cv. TAM 304), moderately susceptible (cv. TAM 111) and susceptible (cv. TAM 112).  Quilt^® fungicide (Azoxystrobin + Propiconazole), was chosen for this experiment because of it’s efficacy on Puccinia pathogens.  Five application timings were developed: 1) an untreated control, 2) flag leaf emergence [8.0], 3) a double application at flag leaf emergence [8.0] and full flag [9.0], 4) a single application at boot [10.0], and 5) four applications from flag leaf emergence through flowering [8.0, 9.0, 10.0, and 10.5].  Treatment 5 was developed to keep each variety disease free, and allow for maximum yield potential.  Data analyzed included leaf rust incidence and severity, yield, test weight, and protein content.  Variety resistance had a significant impact on yield in all years of the experiment.  The multi-year analysis showed Fannin (resistant) had no statistical difference among fungicide treatments.  On the other hand, TAM 111 and 112 responded favorably to all fungicide applications and TAM 304 responded favorably to treatments 3 and 5.  When examining the application timings over all three years, the double application appeared to be the most effective across TAM 111, 112, and 304.  The application of Quilt^® on a highly susceptible variety, like TAM 112, was economically beneficial, in some cases yielding up to 1,000 kg/ha higher than the untreated control.  On the other hand, the application of a foliar fungicide on a resistant variety (Fannin) was not economically efficient, even under severe leaf and stripe rust pressure.