Evaluation of Foliar Fungicides for Control of Stripe Rust on Winter Wheat in Pullman, WA, 2024

Authors: Chen, Xianming; Evans, Conrad; Messerlie, Peter

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2025
Publication Date: 3/31/2025
Citation: Chen, X., Evans, C.K., Messerlie, P.M. 2025. Evaluation of Foliar Fungicides for Control of Stripe Rust on Winter Wheat in Pullman, WA, 2024. Plant Health Progress. https://doi.org/10.1094/PHP-01-25-0022-PDMR.
DOI: https://doi.org/10.1094/PHP-01-25-0022-PDMR

Interpretive Summary: Stripe rust is an important disease of wheat, and the disease can be effectively controlled by applying fungicides when needed. This study was conducted in a field near Pullman, WA under the natural infection of the stripe rust pathogen during the 2023-2024 crop season to determine the efficacy of 15 fungicide treatments on control of stripe rust on winter wheat. The field was planted with susceptible variety 'PS 279' in the fall of 2023 and divided into plots in spring 2024. The first fungicide application timing at the early jointing stage was made on 15 May 2024 when stripe rust was in early development (1-4% severity), and the second application timing at the boot stage was conducted on 30 May when stripe rust was 30-55% severity in non-spray plots. Rust severity was assessed for each plot four times from 14 May to 21 June. Grain yield and test weight were measured at the harvest. Rust severity, test weight, and yield data were analyzed. All treatment significantly reduced overall stripe rust severity with 7 treatments of two applications providing better control of stripe rust than the eight treatments with only one application. All treatments, except one, had significantly higher test weight than the non-treated check. All treatments produced grain yield higher than the non-treated check with two treatments producing the greatest yield. The significant yield increases by the fungicide treatments ranged from 12.0 bu/A (24.1%) to 54.6 bu/A (109.5%). The results can be used for growers to select fungicides and timings of application for reducing wheat yield losses by stripe rust.

Technical Abstract: The study was conducted in a field with Palouse silt loam soil near Pullman, WA. Stripe rust 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 30 Oct 23. Urea fertilizer (46-0-0) was applied at the rate of 100 lb/A at the time of planting. Herbicides (Huskie, 15 fl oz/A and Axial Star, 16.4 fl oz/A plus M-90, 0.25% v/v) were applied to the entire field to control weeds on 15 May 24 when wheat plants were at the early jointing stage (Feekes 5). Before the first fungicide application, the field was divided into individual plots of 4.5-ft (4 rows) in width and 15.0 to 18.9-ft in length by eliminating plants between plots by spraying herbicide (Glystar 5 Extra, 24.0 ml/gal plus M-90 0.25% v/v). Fungicides were applied in 16 gal water/A on different dates and stages depending upon the treatment. The first fungicide application timing at the early jointing stage (Feekes 5) was made on 15 May when stripe rust was 1.0 to 4.0% severity in all plots. The second application at the boot stage (Feekes 10) was conducted on 30 May when stripe rust was 30 to 55% severity in unsprayed plots. A 601C backpack sprayer was used with a CO2-pressurized spray boom at 18 psi having three operating 0.25-in. nozzles spaced 19-in. apart. A randomized complete block design was used with four replications. Rust severity (percentage of infected foliage per whole plot) was assessed for each plot on 14 May, 29 May, 12 Jun, and 21 Jun, or 1 day before and 14, 28, and 37 days after the first fungicide application timing, respectively. Plots were harvested on 1 Aug when kernels had 13 to 15% kernel moisture, and grain yield and test weight of kernels was measured for each plot. Area under disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. Relative AUDPC (rAUDPC) was calculated as percent of the non-treated check. Rust severity, rAUDPC, test weight, and yield data were subjected to analysis of variance, and means were separated by Fisher's protected LSD test. Stripe rust was first observed in the field on 9 Apr, developed to 1 to 4% severity in every plot by 14 May, and reached 95 to 100% severity at the milk stage (Feekes 11.1) in the non-treated check by 21 Jun. The rAUDPC values (9.9 to 78.2%) of all fungicide treatments were significantly less than the non-treated check (100%). The seven treatments with two applications provided better control of stripe rust than the eight treatments with only one application, with the treatment of Trivapro applied at 9.4 fl oz/A at Feekes 5 and 13.7 fl oz/A at Feekes 10 having the lowest rAUDPC value. All treatments had significantly greater test weight than the non-treated check, except the treatments of Tilt 4.0 fl oz/A and Trivapro 9.4 fl oz/A applied at Feekes 5. All treatments produced grain yield significantly greater than the non-treated check with the treatment of Tilt 4.0 fl oz/A applied at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 10 producing the greatest yield. The significant yield responses ranged from 12.0 bu/A (24.1%) by the treatment of Quadris 6.0 fl oz/A at Feekes 5 to 54.6 bu/A (109.5%) by the treatment of Tilt 4.0 fl oz/A applied at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 10.