Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2019
Publication Date: 2/11/2019
Citation: Chen, X., Sprott, J.A., Evans, C.K., Liu, Y. 2019. Evaluation of Pacific Northwest winter wheat cultivars to fungicide application for control of stripe rust in 2018. Plant Disease Management Reports. 13:CF066.
Interpretive Summary: Fungicide application is needed to control stripe rust on wheat varieties without an adequate level of resistance. To determine responses to fungicide application, 23 winter wheat varieties widely grown in the U.S. Pacific Northwest plus a susceptible check were tested in a field near Pullman, WA in the 2017-2018 growth season. For the spray plots, fungicide, Quilt Xcel, was applied at the beginning of the rust season and again at the flag-leaf stage. Stripe rust severity was assessed for each plot four times and grain test weight and yield were measured. Relative area under disease progress curve (rAUDPC) was calculated using the severity data. The fungicide application significantly reduced stripe rust rAUDPC by 93% in the susceptible check and rust reduction was also signifcant in 9 of the 23 commercially grown varieties. The fungicide application significantly increased grain test weight of the susceptible check and three commercial varieties. Significantly higher grain yield was observed in the susceptible check and nine commercial varieties of the sprayed plots than the non-sprayed plots, and the increases ranged from 19 to 70 bu/A, whereas the 14 remaining varieties did not have significant diffences in yield, indicating adequate resistance. Based on the yield data, stripe rust caused yield loss of 70 bu/A (71%) for the susceptible check and significant losses of 19-37 bu/A (11-29%) for the commercial varieties without adequate resistance. The results can be used 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. Ammonium nitrogen fertilizer was applied at 100 lb/A at the time of planting. Winter wheat genotype ‘PS 279’ was used as a susceptible check, and 23 cultivars were selected based on their acreage planted in the state of Washington in 2016 or new releases. 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 Oct 16. The plots were 4.5 ft in width and 14.9 to16.3 ft in length. 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 Apr when wheat plants were at the early jointing stage (Feekes 4). On 8 May when most plants were at the early jointing stage (Feekes 5), 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 stripe rust had started developing on the susceptible check PS 279 plants (2-5% 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 diseased foliage per whole plot) was assessed from each plot on 9 May at the early jointing stage (Feekes 6), 24 May at the late jointing stage (Feekes 8), 7 Jun at the flowering stage (Feekes 10.51), and 22 Jun at the soft dough stage (Feekes 11.1) or 1, 16, 30, and 45 days after the fungicide application. Plots were harvested on 10 Aug when kernels had 3 to 5% 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 control. 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. A natural infection of stripe rust was first observed on PS 279 in early May, approximately one week earlier than normal for the area. The disease reached 30% severity in the non-sprayed susceptible check plots on 24 May (Feekes 8), 16 days after the fungicide was applied; 90% severity on 7 Jun (Feekes 10.51), 30 days after the fungicide application; and 100% on 22 Jun (Feekes 11.1), 45 days after the fungicide application in the plots of the susceptible check without fungicide application. The application of Quilt Xcel at 14 fl oz/A reduced rAUDPC by 88% in the susceptible check plots. The fungicide application also significantly reduced rAUDPC of 18 commercial cultivars (Xerpha, ORCF-102, Eltan, SY 107; Keldin, Whetstone, Otto, UI Sparrow; SY Ovation; Westbred 528, ARS-Crescent, Jasper, Puma, Rosalyn, Skiles, Farnum, Madsen, and Legion, but the reductions were not significant for the remaining 5 cultivars (Norwest 553, LCS Jet, Bruehl, Cara, and Bobtail) as rust severity was low in both non-sprayed and sprayed plots. The fungicide application significantly increased grain test weight of the susceptible check (PS 279) and nine cultivars (Xerpha, ORCF-102, Eltan, SY 107, Keldin, Whetstone, UI Sparrow, Puma, and Cara) by 1.4 to 4.3 lb/bu. The fungicide application made significant yield differences for the susceptible check (95.2 bu/A more in the sprayed plots) and 13 commercial cultivars (Xerpha, ORCF-102, Eltan, SY 107; Keldin, Whetstone, Otto, UI Sparrow; SY Ovation; Westbred 528, ARS-Crescent, LCS Jet, and Jasper) with 16.5 to 87.7 bu/A more grain in the sprayed plots. The remaining 10 cultivars (Norwest 553, Puma,