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

Authors: Chen, Xianming; Sprott, Jason; Evans, Conrad

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. 2023. Evaluation of Pacific Northwest spring wheat cultivars to fungicide application for control of stripe rust in 2022. Plant Disease Management Reports. 17. Article CF032.

Interpretive Summary: Stripe rust is one of the most destructive diseases of spring 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 spring wheat varieties widely grown in the U.S. Pacific Northwest plus a susceptible check in a field near Pullman, WA during the 2022 growth season. The field was planted on 23 April, and plants were inoculated on 26 May with spores of the wheat stripe rust pathogen collected from a winter wheat field on the same farm. For the spray plots, fungicide Quilt Xcel was applied on 15 June at the early jointing stage when rust was just appeared (0.1% severity) in some of the plots and again on 1 July at the boot stage when rust was 15-20% severity in non-sprayed susceptible check plots. Stripe rust severity was recorded five times from 15 June to 22 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 five sets of severity data. The fungicide application significantly reduced stripe rust rAUDPC by 98.1% in the susceptible check, and rust reduction was also signifcant in 8 of the 23 commercially grown varieties. The fungicide application significantly increased grain test weight of the susceptible check by 6.7 pounds per bushel and two commercial varieties by 3.1 or 5.3 pounds per bushel. Significantly higher grain yield was observed in the susceptible check and 3 commercial varieties of the sprayed plots than the non-sprayed plots, whereas the 20 remaining varieties did not have significant diffences in yield, indicating adequate resistance. Based on the yield data, stripe rust caused yield loss of 39.4 bushels per acre (51.9%) for the susceptible check and 4.4 bushels per acre (6.3%) on average for the commercial varieties. The results are useful for managing stripe rust based on individual spring 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. Spring wheat genotype 'AvS' 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 23 Apr 22. The plots were 4.5-ft in width and 15.1 to 17.2-ft in length. Ammonium nitrogen fertilizer was applied at 100 lb/A at the time of planting and again on 17 May at the same rate when plants were at the middle tillering stage (Feekes 2). The field was inoculated on 26 May (Feekes 3) with fresh urediniospores of the wheat stripe rust pathogen collected from a winter wheat experimental field that was inoculated with urediniospores 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 9 Jun when wheat plants were at the early jointing stage (Feekes 4). On 15 Jun when most plants were at the early jointing stage (Feekes 5) and stripe rust just appeared (0.1% severity) in about 50 of the 192 plots, 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 Jul when plants were at the boot stage (Feekes 10) and stripe rust in the non-sprayed AvS plots was 15-20% 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 15 Jun at the early jointing stage (Feekes 5), 30 Jun at the boot stage (Feekes 10), 8 Jul at the boot to late flowering stage (Feekes 10.53), 15 Jul at the milk stage (Feekes 11.1), and 22 Jul at the soft dough stage (Feekes 11.2) or just before and 15, 23, 30, and 37 days after the first time of the fungicide application. Plots were harvested on 26 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 AvS plants in the nursery on 1 Jun 22 and reached 100% severity by 22 Jul at the soft dough stage (Feekes 11.2) in the non-sprayed susceptible check plots. The two applications of Quilt Xcel at 14 fl oz/A reduced rAUDPC by 98.1% in the susceptible check (AvS) plots. The fungicide applications also significantly reduced rAUDPC of eight commercial cultivars (WB6341, WB-1035CL+, Diva, Kelse, Buck Pronto, Whit, Louise, and Glee), and the reduction ranged from 9.9 to 56.0%. The fungicide applications significantly protected grain test weight of the susceptible check (AvS) by 6.7 lb/bu and two commercial cultivars (WB6341 and WB-1035CL+) by 3.1 and 5.3 lb/bu, respectively. The fungicide applications made significant yield differences for the susceptible check (39.4 bu/A more in the sprayed plots) and three commercial cultivars (WB6341, WB-1035CL+, and Net CL+) with 31.8, 21.6, and 13.1 bu/A more grain in the sprayed plots, respectively. The remaining 20 commercial cultivars (Diva, Kelse, Alum, Melba, Ryan, Buck Pronto, Solano, WB9668, Whit, Louise,