Evaluation of Pacific Northwest spring wheat cultivars for response to stripe rust and fungicide application in Pullman, WA, 2024

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

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2025
Publication Date: 3/25/2025
Citation: Chen, X., Evans, C.K., Messerlie, P.M. 2025. Evaluation of Pacific Northwest spring wheat cultivars for response to stripe rust and fungicide application in Pullman, WA, 2024. Plant Health Progress. https://doi.org/10.1094/PHP-01-25-0024-PDMR.
DOI: https://doi.org/10.1094/PHP-01-25-0024-PDMR

Interpretive Summary: Stripe rust is a damaging disease of spring wheat, and the disease can be effectively controlled by planting resistant varieties and applying fungicides when needed. This study was conducted in a field near Pullman, WA under the natural infection of the stripe rust pathogen in the 2024 crop season to determine yield losses by stripe rust and increases by fungicide for 23 major spring wheat varieties plus a susceptible check. The field was planted in the spring of 2024. For the spray plots, fungicide Quilt Xcel was applied at the early jointing stage and also the boot stage. Stripe rust severity was recorded four times from the early jointing to soft dough stage, and grain test weight and yield were measured for each plot at harvest. Relative area under the disease progress curve value (rAUDPC) was calculated using the four sets of severity data. The fungicide application significantly reduced stripe rust rAUDPC by 93.5% in the susceptible check, and rust reduction was also signifcant in 11 of the 23 commercially grown varieties. The fungicide application significantly increased grain test weight of the susceptible check and two commercial varieties. Significantly higher grain yield was observed in the susceptible check and one commercial varieties of the sprayed plots than the non-sprayed plots, whereas the remaining 22 varieties did not have significant diffences in yield, indicating adequate resistance. Based on the yield data, stripe rust caused yield loss of 20.1 bushels per acre (29.6%) for the susceptible check and 3.2 bushels per acre (4.5%) on average for the commercial varieties. The results are useful for growers to select spring wheat varieties to grow for high-yielding without use of fungicides.

Technical Abstract: This study was conducted in a field near Pullman, WA under the natural infection of the stripe rust pathogen to evaluate the control of stripe rust with fungicide applications on major spring wheat cultivars grown in the U.S. Pacific Northwest and assess yield loss caused by the disease. Spring wheat genotype 'AvS' was used as a susceptible check, and 23 cultivars were selected based on their high acreage planted in Washington state in 2023. The 24 entries were arranged in a randomized complete plot design with a split-block constraint based on fungicide application, with four replications. They were seeded in rows spaced 14-in. apart at 60 lb/A (99% germination rate) with a drill planter on 1 May 24. The plots were 4.5-ft in width and 15.3 to 18.4-ft in length. Ammonium nitrogen fertilizer was applied at 100 lb/A at the time of planting. Due to a planting error in the first replication, this replication was discarded from the experiment. Herbicide Agristar 5 24 fl oz/A, plus M-90 10.4 fl oz/A, was applied on 7 Jun when wheat plants were at the early jointing stage (Feekes 4). On 13 Jun when most plants were at the early jointing stage (Feekes 5) and stripe rust was absent, Quilt Xcel 2.2SE was sprayed at the rate of 14.0 fl oz/A mixed with 0.25% v/v M-90 in 16-gallon water/A and sprayed again at the same rate on 28 Jun when plants were at the boot stage (Feekes 10.1) and stripe rust reached 15-20% in the non-sprayed AvS plots. A 601C backpack sprayer was used with a CO2-pressurized spray boom at 18 psi having three operating ¼ in. nozzles spaced 19-in. apart. Rust severity (percentage of stripe rust infected foliage per whole plot) was assessed from each plot on 13 Jun at the early jointing stage (Feekes 5), 28 Jun at the boot stage (Feekes 10.1), 9 Jul at the milk stage (Feekes 10.54), and 21 Jul at the soft dough stage (Feekes 11.1) or 0, 15, 26, and 38 days after the first time of the fungicide application. Plots were harvested on 20 Aug when kernels had 13 to 15% kernel moisture and test weight of kernels was measured. Area under the 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 susceptible check. rAUDPC, test weight, and yield data were subjected to analysis of variance, and the effect of fungicide application on rAUDPC, test weight, and yield was determined in comparison with non-sprayed plots for each cultivar by Fisher's protected LSD test. Stripe rust was first observed on AvS plants on 20 Jun and reached 90-95% severity by 21 Jul at the soft dough stage (Feekes 11.1) in the non-sprayed susceptible check plots. The two applications of Quilt Xcel at 14 fl oz/A reduced rAUDPC by 93.5% in the susceptible check (AvS) plots. The fungicide applications also significantly reduced rAUDPC of 11 commercial cultivars (UI Stone, Kelse, Net CL+, Roger, UI Cookie, Alum, Chet, Buck Pronto, Louise, Ryan, and Glee), and the reduction ranged from 7.4 to 53.5%. The grain test weight was significantly higher in the sprayed plots than the non-sprayed plots of the susceptible check AvS (by 3.1 lb/bu), UI Stone (by 1.9 lb/bu), and Buck Pronto (2.0 lb/bu). The fungicide applications made significant yield differences for AvS (20.1 bu/A more grain in the sprayed plots than the non-sprayed plots) and UI Stone (19.0 bu/A more grain in the sprayed plots than the non-sprayed plots). The remaining 22 cultivars (Kelse, Net CL+, Expresso, Roger, UI Cookie, Alum, WB9668, Chet, Buck Pronto, Melba, Louise, WA 8351, AP Mondovi, Ryan, Seahawk, Hale, Hedge CL+, AP Venom, Glee, Tekoa, JD, and AB9662) did not show significant yield difference, indicating adequate resistance to stripe rust under the disease pressure. Based on the yield data between the fungicide sprayed and non-sprayed plots, stripe rust reduced yield by 29.6% in the sus