Evaluation of Pacific Northwest spring wheat cultivars to fungicide application for control of stripe rust in 2023

Authors: Chen, Xianming; Evans, Conrad

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2024
Publication Date: 3/12/2024
Citation: Chen, X., Evans, C.K. 2024. Evaluation of Pacific Northwest spring wheat cultivars to fungicide application for control of stripe rust in 2023. Plant Disease Management Reports. 18. Article CF067.

Interpretive Summary: Stripe rust causes major losses in spring wheat in the Pacific Northwest, and the disease is controlled by planting resistant varieties and applying fungicides. This study was conducted in a field near Pullman, WA during the 2023 growth 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 on 3 May and inoculated on 2 Jun with wheat stripe rust spores. For the spray plots, fungicide Quilt Xcel was applied on 7 June at the early jointing stage and again on 21 June at the boot stage. Stripe rust severity was recorded five times from 8 June to 17 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. Due to the drought conditions, stripe rust was developing slowly and did not reach uniform and adequate levels to distinguish between the treated and non-treated plots for most of the cultivars. The fungicide application significantly reduced stripe rust rAUDPC by 99.8% in the susceptible check, and rust reduction was also signifcant in three commercial varieties. However, the fungicide applications did not make significant differences in grain test weight and yield between the fungicide-sprayed and non-spray plots for all cultivars including the susceptible check. The mean yield of the non-spray plots was 87.3 bu/A and the mean yield of the fungicide-sprayed plots was 87.0 bu/A, indicating that under such low stripe rust pressure, fungicide applications did not increase grain yield. The wide yield range, 57.0-114.2 bu/A, can be useful for selecting high-yielding cultivars to grow.

Technical Abstract: This study was conducted in a field near Pullman, WA 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 the state of Washington in 2022. 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 3 May 23. 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. The field was inoculated on 2 Jun (Feekes 3-4) 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 2022. Herbicides (Huskie 15.0 fl oz/A + Axial XL 16.4 fl oz/A + M-90 10.4 fl oz/A) were applied on 5 Jun when wheat plants were at the early jointing stage (Feekes 4-5). On 7 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 21 Jun when plants were at the boot stage (Feekes 10) and stripe rust appeared 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 8 Jun at the early jointing stage (Feekes 5), 15 Jun at the late jointing stage (Feekes 8), 28 Jun at the heading stage (Feekes 10.2), 10 Jul at the milk stage (Feekes 10.54), and 17 Jul at the soft dough stage (Feekes 11.1) or 1, 8, 21, 33, and 40 days after the first time of the fungicide application. Plots were harvested on 28 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 on 15 Jun 23 and reached 50-90% severity by 17 Jul at the soft dough stage (Feekes 11.1) in the non-sprayed susceptible check plots. Due to the drought conditions, stripe rust was developing slowly and did not reach uniform and adequate levels to distinguish between the treated and non-treated plots for most of the cultivars. The two applications of Quilt Xcel at 14 fl oz/A reduced rAUDPC by 99.8% in the susceptible check (AvS) plots. The fungicide applications also significantly reduced rAUDPC of three commercial cultivars (WB-1035CL+, Kelse, and Buck Pronto), and the reduction ranged from 7.2 to 29.4%. However, the fungicide applications did not make significant differences in grain test weight and yield between the fungicide-sprayed and non-spray plots for all cultivars including the susceptible check. The mean yield of the non-spray plots was 87.3 bu/A and the mean yield of the fungicide-sprayed plots was 87.0 bu/A, indicating that under such low stripe rust pressure, fungicide applications did not increase grain yield. The wide yield range, 57.0-114.2 bu/A, can be useful for selecting high-yielding cultivars to grow.