Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2016
Publication Date: 12/30/2016
Citation: Chen, X., Evans, C.K., Sprott, J.A., Liu, Y. 2016. Evaluation of winter wheat cultivars to fungicide application for control of stripe rust in 2016. Plant Disease Management Reports. 11:CF015.
Interpretive Summary: Wheat stripe rust is primarily controlled by growing resistant cultivars and secondarily by fungicides. To evaluate winter wheat cultivars for their yield losses caused by stripe rust and responses to fungicide applications, 23 winter wheat cultivars widely grown in the Pacific Northwest plus a susceptible check were tested in a field near Pullman, WA under natural infection of the stripe rust pathogen. Stripe rust severity was assessed for each plot four times and grain test weight and yield were measured. Area under disease progress curve (AUDPC) was calculated for each plot using the severity data. The the fungicide applications significantly reduced the rAUDPC for the susceptible check and 12 of the commercial cultivars, but reductions were not significant for the remaining 11 cultivars with greater levels of resistance . The fungicide applications significantly increased grain test weight of the susceptible check and five cultivars by 1.8 to 5.0 lb/bu. The fungicide applications increased yield by -6.6 (-4.5%) to 66.2 bu/A (249.0%) in the 24 entries, but the increases were significant only for the susceptible check and five cultivars. Yield losses were estimated as 66.2 bu/A (71.4%) for the susceptible check and -6.6 to 46.6 bu/A (-4.7 to 32.1%) for the commercially grown cultivars at average of 8.0%. This study indicated that under the severe stripe rust epidemic in 2016, most winter wheat cultivars had adequate levels of resistance and about 20% of the cultivars needed at least two applications of fungicides.
Technical Abstract: To evaluate winter wheat cultivars grown in the U.S. Pacific Northwest to fungicide application for control of stripe rust and assess their yield loss caused by the disease, this study was conducted in a field near Pullman, WA. 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 2015 or new releases. The 24 entries were arranged in a randomized complete block design with a split block based on spray or not spray and with four replications. They were seeded in rows spaced 14-in. apart at 60 lb/A (99% germination rate) with a drill planter on 20 Oct 15. The plots were 4.5 ft in width and 14.0 to16.4 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 22 Apr when wheat plants were at the early jointing stage (Feekes 4). Fungicide, Quilt 1.66SE, was sprayed at the rate of 14.0 fl oz/A mixed with M-90 at the rate of 14.0 fl oz/A in 16 gallon water/A on 10 May when most plants were at the early jointing stage (Feekes 5) and stripe rust started developing on the susceptible check PS 279 plants (3-5% severity) and sprayed again at the same rate on 7 Jun (28 days after the first application) when the plants were at the flowering stage (Feekes 10.5) and stripe rust reached 100% severity in the non-treated susceptible check 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. Disease severity (percentage of diseased foliage per whole plot) was assessed from each plot on 10 May at the early jointing stage, 23 May at the boot stage, 7 Jun at the flowering stage, and 20 Jun at the soft dough stage or 0, 13, 28, and 41 days after the first fungicide application. Plots were harvested on 16 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 three 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 reduction and test weight and yield increases for each cultivar was determined by Fisher’s protected LSD test. A natural infection of stripe rust was first observed on PS 279 in late April, approximately two weeks earlier than normal for the area. The disease reached 80% severity in the non-sprayed susceptible check plots on 23 May (boot stage), 13 days after the fungicide was first applied, and 100% on 7 Jun (flowering stage) in the plots of the susceptible check without fungicide application. The two applications of Quilt at 14 fl oz/A did not completely prevent stripe rust infection, mainly due to the fact that the second application was later than the optimal timing as disease severity reached 80% when the second application was made. However, fungicide applications significantly reduced the rAUDPC for the susceptible check, but the reduction was only 43%. The fungicide applications also significantly reduced rAUDPC for cultivars Xerpha, Eltan, ORCL-103, ORCF-102, Whetstone, Keldin, ARS-Crescent, Westbred 528, Puma, ARS-Crystal, Jasper, and WB 523, but the reductions were not significant for the remaining 11 cultivars with greater levels of resistance as rust severity was low in both non-sprayed and sprayed plots. The fungicide applications significantly increased grain test weight of the susceptible check (PS 279) and cultivars Xerpha, Eltan, ORCF-103, ORCF-102 and ARS-Crystal by 1.8 to 5.0 lb/bu. The fungicide applications increased yield by -6.6 (-4.5%) to 66.2 bu/A (249.0%) in the 24 entries, but the increases were significant onl