Control of stripe rust of winter wheat with foliar fungicides, 2011

Authors: Chen, Xianming; Evans, Conrad; Garner, John

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2012
Publication Date: 3/30/2012
Citation: Chen, X., Evans, C.K., Garner, J.P. 2012. Control of stripe rust of winter wheat with foliar fungicides, 2011. Plant Disease Management Reports. 6:032.

Interpretive Summary: A total of 15 fungicide treatments were tested for their efficacy in control of stripe rust on winter wheat during the 2010-2011 crop season. The experimental field near Pullman, WA was planted with a susceptible winter wheat cultivar, PS 279, on October 20, 2010. A randomized complete block design experiment with four replications was used including a non-treated check treatment. Fungicides were applied on two different dates and stages depending upon the treatments. Disease severity was assessed from each plot five 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 percentage of the non-treated control. Grain yield 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. Stripe rust caused more than 90% yield loss in the non-treated control plots. All fungicide treatments significantly reduced rust severity compared to the non-treated control at heading stage. Some of the treatments provided better control than others. Except three only jointing-stage applications and one treatment at boot stage, all treatments significantly increased test weight. All treatments, except one, significantly increased grain yield compared to the non-treated control. Yield increases ranged from 93.7% to 862.8%.

Technical Abstract: The study was conducted in a field with Palouse silt loam under natural infection of stripe rust near Pullman, WA. Fertilizer (Osmocota 14-14-14) was applied at 60 lb/A at the time of cultivation. Susceptible ‘PS 279’ winter club wheat was seeded in rows spaced 14 in. apart at 60 lb/A (99% germination rate) with a drill planter on 20 Oct 10. Huskie 15 fl oz plus R-11 30 ml/A was applied on 1 Jun 11 when wheat plants were at early jointing stage. Before the first fungicide application, the field was divided into individual plots of 4.4 ft (4 rows) in width and 15.0-17.5 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 jointing stage was done on 3 Jun when stripe rust was 10-30% severity and the second at boot stage on 17 Jun when stripe rust in the unsprayed plots reached 70-90% 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 3 Jun, 16 Jun, 28 Jun, 11 Jul, and 25 Jul or on the same day and 13, 25, 38, and 52 days after the first fungicide application timing, respectively. Plots were harvested on 30 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. Because the considerable level of stripe rust had developed by the fungicide application dates, none of the fungicide treatments provided complete protection of the crop from the disease. However, all fungicide treatments significantly reduced rust severity compared to the non-treated control at heading stage. Relative AUDPC values of all treatments were significantly less than the non-treated control, and were significantly different among some of the treatments. Priaxor (2 fl oz/A), Headline (3 fl oz/A), and Tilt (2 fl oz/A) applied at jointing stage and Priaxor (4 fl oz/A), Tilt (4 fl oz/A), and Absolute (5 fl oz/A) applied at boot stage had similar relative AUDPC values, which were significantly lower than that of the non-treated control, but significantly higher than some of the remaining treatments with Twinline, Priaxor, Quilt, Stratego, DPX-LEM17, or combinations of different fungicides. Two applications of different fungicides, Priaxor (2.0 fl oz/A at jointing stage) plus Twinline (7 fl oz/A at boot stage) and Headline (3 fl oz/A at jointing stage) plus Priaxor (4 fl oz/A at boot stage), had the lowest relative AUDPC values. The three only jointing applications (Priaxor 2 fl oz/A, Headline 3 fl oz/A, and Tilt 2 fl oz/A) had test weight significantly lower than the non-treated control. All of the remaining treatments, except the treatment of Priaxor 4 fl oz/A applied at boot stage, significantly increased test weight. All treatments, except the treatment of Tilt (4 fl oz/A) applied at boot stage, significantly increased grain yield compared to the non-treated control. Yield increases ranged from 93.7% by the treatment of Tilt at the rate of 4 fl oz/A at boot stage to 862.8% by the treatment of Priaxor (3 fl oz/A) applied at jointing plus Twinline (7 fl oz/A) applied at boot stage. The non-treated control plots produced only 10% grain of the best treatments.