Citation: Chen, X., Wood, D.A. 2011. Control of stripe rust of winter wheat with foliar fungicides, 2010. Plant Disease Management Reports. 5:CF004. Interpretive Summary: A total of 12 fungicide treatments plus a non-treated control were tested for their efficacy in control of stripe rust on winter wheat during the 2009-2010 crop season. The experimental field near Pullman, WA was planted with a susceptible winter wheat cultivar, PS 279, on October 26, 2009. An randomized complete block design with four replications was used including a non-treated check treatment. Fungicides were applied on different dates and stages depending upon the treatments. Disease severity was assessed from each plot four times during the disease season under the natural infection of stripe rust. Area under the disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. Relative AUDPC was calculated as percent of the non-treated control. Grain yield and and test weight were measured. Rust severity, relative AUDPC, test weight, and yield data were subjected to analysis of variance and means were compared to determine the difference among the treatments. All fungicide treatments significantly reduced rust severity compared to the non-treated control at flowering stage. The 12 treatments were statistically separated into two groups: 4 provided moderate control and 8 provided the best control. Ten of the 12 treatments significantly increased test weight and all 12 treatments significantly increased grain yield compared to the non-treated control. Yield increases ranged from 34.6% to 147.2%. The information is useful for controlling stripe rust on winter wheat.
Technical Abstract: The study was conducted in a field with Palouse silt loam under natural infection of stripe rust near Pullman, WA. Urea (46-0-0) was applied at 60 lb/A at the time of cultivation. Susceptible ‘PS 279’ winter wheat was seeded in rows spaced 14 in. apart at 60 lb/A (99% germination rate) with a drill planter on 26 Oct 09. Harmony Extra 0.33 oz plus Buctril 0.75 pt/A with Agridex crop oil concentrate (COC) at 1% of spray volume was applied on 11 May 10 when wheat plants were at late tillering stage. Before the first fungicide application, the field was divided into individual plots of 4.8 ft (4 rows) in width and 16.0-17.8 ft in length by eliminating plants between plots with a rototiller. Fungicides were applied in 16 gal water/A on different dates and stages depending upon the treatments. The first fungicide application timing at late jointing stage was done on 21 May when stripe rust was just appearing (1% severity) and the second at boot stage on 8 Jun when stripe rust reached 5% severity. A 601C backpack sprayer was used with a CO2 pressurized spray boom at 18 psi having three operating nozzles spaced 19 in apart. A randomized block design was used with four replications. Disease severity (percentage of diseased foliage on whole plot) was assessed from each plot on 8 Jun, 11 Jun, 24 Jun, and 8 Jul or on the same day and 3, 16, and 30 days after the second fungicide application timing, respectively. Plots were harvested on 10 Aug when kernels were naturally dry, and test weight of kernels was measured. Area under disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. Relative AUDPC was calculated as percent of the non-treated control. Rust severity, relative AUDPC, test weight, and yield data were subjected to analysis of variance and means were separated by Fisher’s protected LSD test. All fungicide treatments significantly reduced rust severity compared to the non-treated control at flowering stage. Relative AUDPC values of all treatments were significantly less than the non-treated control, and were significantly different among some of the treatments. Topguard applied at late jointing stage at all three tested rates and applied at 7 fl oz/A at boot stage had similar relative AUDPC values, which were significantly lower than that of the non-treated control, but significantly higher than those of all remaining treatments with Topguard, Quilt, Quilt Xcel, Tilt, Stratego Pro, and Prosaro. Except the treatments of Topguard at 7 and 10 fl oz/A, all treatments significantly increased test weight. All treatments significantly increased grain yield compared to the non-treated control. Yield increases ranged from 34.6% by the treatment of Topguard at the rate of 7 fl oz/A at late jointing to 147.2% by the treatment of Prosaro.