Evaluation of Pacific Northwest winter wheat cultivars to fungicide application for control of stripe rust in 2022

Authors: Chen, Xianming; Sprott, Jason; Evans, Conrad; QIN, RUIJUN - Oregon State University

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2023
Publication Date: 3/15/2023
Citation: Chen, X., Sprott, J.A., Evans, C.K., Qin, R. 2023. Evaluation of Pacific Northwest winter wheat cultivars to fungicide application for control of stripe rust in 2022. Plant Disease Management Reports. 17. Article CF033.

Interpretive Summary: Stripe rust is one of the most destructive diseases of winter wheat in the Pacific Northwest, and the disease is controlled by planting resistant varieties and applying fungicides if varieties do not have adequate resistance. This study was conducted to determine yield losses by stripe rust and responses to fungicide application for 23 winter wheat varieties widely grown in the U.S. Pacific Northwest plus a susceptible check in a field near Pullman, WA during the 2021-2022 growth season. The field was planted on 2 November 2021, and plants were inoculated in spring 2022 with spores of the wheat stripe rust pathogen collected from the same location in 2021. For the spray plots, fungicide Quilt Xcel was applied on 10 May 2022 at the early jointing stage when rust was absent and again on 1 June at the late jointing stage when rust was 0.5-5% severity in non-sprayed susceptible check plots. Stripe rust severity was recorded six times from 10 May to 5 July, and grain test weight and yield were measured for each plot at harvest. Relative area under the disease progress curve (rAUDPC) was calculated using the six sets of severity data. The fungicide application significantly reduced stripe rust rAUDPC by 70.3% in the susceptible check, and rust reduction was also signifcant in 12 of the 23 commercially grown varieties. The fungicide application significantly increased grain test weight of the susceptible check by 3.1 pounds per bushel and four commercial varieties by 1.5 to 14.3 pounds per bushel. Significantly higher grain yield was observed in the susceptible check and 17 commercial varieties of the sprayed plots than the non-sprayed plots, whereas the 6 remaining varieties did not have significant diffences in yield, indicating adequate resistance. Based on the yield data, stripe rust caused yield loss of 57.4 bushels per acre (83.6%) for the susceptible check and 16.8 bushels per acre (14.4%) on average for the commercial varieties. The results are useful for managing stripe rust based on individual winter wheat varieties.

Technical Abstract: This study was conducted in a field near Pullman, WA to evaluate the control of stripe rust with fungicide applications on major winter wheat cultivars grown in the U.S. Pacific Northwest and assess yield loss caused by the disease. Winter wheat genotype 'PS 279' was used as a susceptible check, and 23 cultivars were selected based on their high acreage planted in the state of Washington in 2021. The 24 entries were arranged in a randomized split block design 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 2 Nov 21. The plots were 4.5-ft in width and 14.3 to 17.1-ft in length. Ammonium nitrogen fertilizer was applied at 100 lb/A at the time of planting and again on 4 Apr 22 at the same rate when plants were at late tillering stage (Feekes 3). The field was inoculated on 21 Mar (Feekes 2), 3 Apr (Feekes 3), and 29 Apr (Feekes 4) with urediniospores of the wheat stripe rust pathogen collected from the same farm in 2021. Herbicides (Huskie 15.0 fl oz/A + Axial XL 16.4 fl oz/A + M-90 10.4 fl oz/A) were applied on 21 May when wheat plants were at the early jointing stage (Feekes 5). On 10 May when most plants were at the early jointing stage (Feekes 4-5) and stripe rust was not observed, 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 1 Jun when plants were at the late jointing stage (Feekes 7-8) and stripe rust in the non-sprayed PS 279 plots was 0.5-5% severity. 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. Disease severity (percentage of stripe rust infected foliage per whole plot) was assessed from each plot on 10 May at the early jointing stage (Feekes 4-5), 31 May at the late jointing stage (Feekes 7-8), 14 Jun at the boot to late heading stage (Feekes 10.0-10.5), 21 Jun at the early heading to early flowering stage (Feekes 10.2-10.51), 28 Jun at the late flowering to milk stage (Feekes 10.4-10.54), and 5 Jul at the milk to soft dough stage (Feekes 11.1 -11.2) or just before and 21, 35, 42, 50, and 57 days after the first time of the fungicide application. Plots were harvested on 24 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 six 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 PS 279 plants in the nursery on 11 May 22 and reached 100% severity by 21 Jun at the heading to flowering stage (Feekes 10.2-10.51) in the non-sprayed susceptible check plots. The two applications of Quilt Xcel at 14 fl oz/A reduced rAUDPC by 70.3% in the susceptible check (PS 279) plots. Due to the stripe rust favorable cool and wet weather conditions before July, the disease still caused substantial yield losses on susceptible cultivars after the second fungicide application. The fungicide applications also significantly reduced rAUDPC of twelve commercial cultivars (WB4303, UI Magic, LCS Jet, Otto, Mela CL+, Curiosity CL+, Puma, Keldin, SY Ovation, SY Clearstone 2CL, LCS Artdeco, and ARS-Crescent), and the reduction ranged from 9.0 to 58.4%. The fungicide applications significantly protected grain test weight of the susceptible check (PS 279) by 3.1 lb/bu and four commercial cultivars (WB4303, UI Magic, LCS Jet, and Otto) by 1.5 to 14.3 lb/bu. The fungicide applications made significant yield