1997/1998 Septoria Disease Spray Trials at Hyslop Research Farm

Three fungicides: Tilt (propiconazole), Folicur (tubuconazole), and Quadris (azoxystrobin), were examined for their effectiveness at managing the Septoria diseases (Septoria tritici and to a lesser extent S. nodorum). All three fungicides were tested on three soft white, winter wheat cultivars: Foote, Madsen, and Stephens. Granular potassium chloride (KCl) was also tested on Madsen to test its efficacy as an early season disease suppressant. To help determine the optimum spray time, comparisons were made between applying the fungicides at either early flag-leaf emergence or heading. On Madsen and Stephens, comparisons were also made between a single application of Tilt at early flag and two applications of Tilt (first spray at early flag, second spray 17-20 days later). Potassium chloride (100 lb chloride/acre) was applied in granular form in the spring at jointing (GS 31). Experiments were replicated four times at the Hyslop Experiment Station in Corvallis, OR. Plots were rated for Septoria disease severity in early June (GS 71-73). Grain from each plot was harvested July 23^rd and measured for yield (bu/acre), test weight, percent protein, and kernel weight. Below we report the effect of the various treatments on yield and Septoria disease severity.

Quadris is now labeled for wheat in Oregon and most other states. It is important to note that the fungicide Folicur is not currently registered for wheat in Oregon. Furthermore, Tilt cannot be applied past flag leaf emergence and can only be applied once per season. Because these regulations may change, it is important to follow the recent regulations for fungicide application in your area.

Yield response to chemical treatments

For the highly susceptible cultivar Stephens, there was a statistically significant (P= 0.04) increase in yield for the Quadris-Early flag, Tilt-Early flag, and Tilt-Two sprays spray treatments compared to the unsprayed control (Table 1). Among these three treatments there were no significant differences. We were unable to statistically distinguish differences between the treatments including the control with respect to yield for winter wheat cultivars Foote and Madsen ( P > 0.27); therefore, we have not included these data. A lack of significant differences suggests that either there were no significant differences between treatments or variation in field conditions were large enough to obscure differences. We did notice significant variation in our field plots due to factors such as soil compaction from wheel tracks and areas of poor drainage.

Septoria disease response to chemical treatments

For Foote, Madsen, and Stephens, some of the fungicide treatments significantly decreased Septoria disease severity compared to the control (Table 2). For Foote, the largest difference in disease severity between the control and a treatment was only 10%, and thus yield may not have been significantly increased by any of the treatments. Foote may have sufficient resistance to the Septoria diseases to currently eliminate the need for fungicides. The largest difference in disease severity between the control and a treatment was 24% for Madsen and 17% for Stephens (Table 2). Depending upon the cultivar, there were some significant differences in disease severity between the different fungicides and between applying a fungicide at early flag versus heading (Table 2).

Conclusion

Although there were significant differences in disease severity between some treatments for all three cultivars, significant differences in the most important factor, yield, only occurred for the highly susceptible cultivar Stephens. Nevertheless, during heavy disease years it is usually economical to spray Madsen. The Septoria disease severity appears to vary by region, being more severe in the southern part of the Willamette valley than the northern part of the valley. For example, at Hyslop Research Farm (Corvallis) it was economical to spray a fungicide 5 out of 6 years on Madsen. At Aurora (northern valley) however, it was only economical to spray 1 out of 4 years on Madsen according to our earlier research. The cultivar Foote, slated for release in 2000, appears to be resistant enough to the Septoria diseases to obviate the need for a fungicide application. We will continue to evaluate Foote and other cultivars for their sensitivity to the Septoria diseases and their response to fungicide sprays in western Oregon. Tilt is still effective at reducing the severity of the Septoria diseases. The new fungicide Quadris has a different mode of action than Tilt, and appears to be as effective as Tilt in reducing the Septoria diseases. Having two effective fungicides should help minimize fungicide resistance by allowing the alternation between these two fungicides. Folicur, which has a similar mode of action as Tilt, appears to be less effective than Quadris and Tilt. This observation, however, is not conclusive because it is based only on single year’s data. If Tilt and a second fungicide such as Benlate are used according to the regulations, a grower could spray twice per season to control the Septoria diseases. However, according to our current and previous data, spraying twice per season affords no significant decrease in Septoria severity or increase in yield and is therefore unnecessary. For more information about the Septoria diseases and our past research results see Crop Science Report 109 (http://www.css.orst.edu/cereals/wheat/diseases/septoria.htm) or contact J. Pat Martinez at martinej@bcc.orst.edu (phone: 541-737-3557).

This research was funded by the Oregon Wheat Commission and was conducted by S.M. Coakley, J.P. Martinez, R.S. Karow, and E. Marx of Oregon State University.

Table 1. Yield response for the wheat cultivar Stephens to fungicide treatments.

^a Folicur is not registered for wheat in Oregon. Tilt can only be applied once per season and no later than flag leaf emergence. * first spray at early flag and second spray 17-20 days later.

^b Values followed by same letter for a given cultivar are not significantly different at the 95% confidence interval. An increase of ~ 7.5 bu/acre is needed for a fungicide application to be economical. This includes the cost of the fungicide, the "rundown" loss, and wheat selling at $3.50/bu.

Table 2. The effect of chemical treatments on Septoria disease severity on wheat cultivars Foote, Madsen, and Stephens.

^a Folicur is not registered for wheat in Oregon. Tilt can only be applied once per season and no later than flag leaf emergence.

^b Values followed by same letter for a given cultivar are not significantly different at the 95% confidence interval. NA indicates the treatment was not applied to this cultivar.

* First spray at early flag and second spray 17-20 days later.