Evaluation of Pacific Northwest spring wheat cultivars to fungicide application for control of stripe rust in 2020

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

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2021
Publication Date: 3/4/2021
Citation: Chen, X., Sprott, J.A., Evans, C.K. 2021. Evaluation of Pacific Northwest spring wheat cultivars to fungicide application for control of stripe rust in 2020. Plant Disease Management Reports. 15. Article 031.

Interpretive Summary: Growing resistant varieties and applying fungicides if needed are major approaches for control stripe rust. In the present study, we tested 23 spring wheat varieties widely grown in the U.S. Pacific Northwest plus a susceptible check in a field near Pullman, WA in 2000 to determine their yield losses caused by stripe rust and yield increases by fungicide application in comparison to the non-spray checks. For the spray plots, fungicide Quilt Xcel was applied when stripe rust just appreaed. Stripe rust severity was recorded four times, and grain test weight and yield were measured for each plot at harvest. Relative area under disease progress curve (rAUDPC) was calculated using the severity data. The fungicide application significantly reduced stripe rust rAUDPC by 97.1% in the susceptible check and rust reduction was also signifcant in 13 of the 23 commercially grown varieties. The fungicide application significantly increased grain test weight of the susceptible check by 7.9 pounds per bushel and 10 of the 23 commercial varieties by 1.1 to 7.8 pounds per bushel. Significantly higher grain yield was obtained in the susceptible check and 15 commercial varieties of the sprayed plots than the non-sprayed plots, whereas the 8 remaining varieties did not have significant diffences in yield, indicating adequate resistance. Based on the yield data, stripe rust caused yield loss of 93.9 bu/A (83.8%) for the susceptible check and 11.9 bushels per acre (10.7%) on average for the commercial varieties. The results can be used to control stripe rust in an integrated management strategy 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 spring wheat cultivars grown in the U.S. Pacific Northwest and assess yield loss caused by the disease. Spring wheat genotype 'Avocet S' (AvS) was used as a susceptible check, and 23 cultivars were selected based on their high acreage planted in the state of Washington in 2019. 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 27 Apr 20. The plots were 4.5-ft in width and 14.4 to 16.6-ft in length. Ammonium nitrogen fertilizer was applied at 100 lb/A at the time of planting and again on 2 Jun at the same rate when plants were at early jointing stage (Feekes 4). Herbicides (Huskie 15.0 fl oz/A + Axial XL 16.4 fl oz/A + M-90 10.4 fl oz/A) were applied on 4 Jun when wheat plants were at the early jointing stage (Feekes 4). On 18 Jun when most plants were at the middle jointing stage (Feekes 6) and stripe rust was 1-2% severity in the susceptible check 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. 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 17 Jun at the middle jointing stage (Feekes 6), 1 Jul at the heading stage (Feekes 10.2), 15 Jul at the late flowering stage (Feekes 10.54), and 22 Jul at the milk stage (Feekes 11.1) or 1 day before and 13, 27, and 34 days after the fungicide application. Plots were harvested on 27 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 observed on AvS plants in the nursery at the late tillering stage (Feekes 3) and reached 100% severity at the late flowering stage (Feekes 10.54) in the non-sprayed susceptible check plots. The application of Quilt Xcel at 14 fl oz/A reduced rAUDPC by 97.1% in the susceptible check (AvS) plots. The fungicide application also significantly reduced rAUDPC of thirteen commercial cultivars (WB-1035CL+, Kelse, Whit, Solano, Diva, Louise, Net CL+, Chet, Alum, Ryan, Glee, SY Selway, and SY Gunsight), and the reduction ranged from 4.7 to 86.7%. The fungicide application significantly protected grain test weight of the susceptible check (AvS) by 7.9 lb/bu and ten commercial cultivars (WB-1035CL+, Kelse, Whit, Solano, Diva, Louise, Tekoa, Net CL+, Alum, and Glee) by 1.1 to 7.8 lb/bu. The fungicide application made significant yield differences for the susceptible check (93.9 bu/A more in the sprayed plots) and fifteen commercial cultivars (WB-1035CL+, Kelse, Whit, Solano, Diva, Louise, Tekoa, Net CL+, Chet, Alum, Ryan, Melba, Glee, AP Renegade, and SY Selway) with 8.4 to 62.8 bu/A more grain in the sprayed plots. The remaining eight commercial cultivars (Seahawk, SY Gunsight, Expresso, WB9668, WB9662, WB6121, WB7202CLP, and JD) showed no significant yield differences between the no-spray and spray treatments. These data indicated that stripe rust caused yield loss of 93.9 bu/A (83.8%) on the susceptible check and 11.9 bu/A (10.7%) yield loss on average across the commercially grown cultivars under the severe disease pressu