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 spring wheat cultivars to fungicide application for control of stripe rust in 2016. Plant Disease Management Reports. 11:CF014.
Interpretive Summary: Spring wheat cultivars have different levels of resistance to stripe rust and may needed or not need fungicide application under different levels of stripe rust epidemic. To evaluate spring wheat cultivars for their yield losses caused by stripe rust and responses to fungicide applications, 15 spring 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 in 2016. 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 using the severity data. The results showed that the two applications of a fungicide completely controlled stripe rust. The fungicide applications significantly increased grain test weight of the susceptible check (AvS), but not of any of the cultivars. The fungicide applications significantly increased the grain yields of the susceptible check and eight of the cultivars, and the increases ranged from 14.9 to 40. 9 bu/A (17.8-119.8%), whereas the seven remaining cultivars did not have significant yield increases. Based on the yield data, stripe rust caused yield loss of 40.9 bu/A (54.5%) for the susceptible check and losses of -2.5 to 41.4 bu/A (-3.1 to 42.5%) for the cultivars at average of 19.9%. This study indicated that under the severe stripe rust epidemic in 2016, about 50% of the spring wheat cultivars had adequate levels of resistance and another 50% of the cultivars needed two applications of fungicides.
Technical Abstract: To evaluate spring 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. Spring wheat genotype ‘Avocet S’ (AvS) was used as a susceptible check, and 15 spring wheat cultivars were selected based on their acreage planted in the state of Washington in 2015 or new releases. The 16 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 3 May 16. The plots were 4.5 ft in width and 15.0 to16.9 ft in length. Urea (46N-0P-0K) was applied at 100 lb/A on 27 May when plants were at tillering stage (Feekes 2). Herbicides (Huskie 15.0 fl oz/A + Axial XL 16.4 fl oz/A + M-90 10.4 fl oz/A) were applied on 30 May when wheat plants were at the tillering stage (Feekes 2-3). 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 7 Jun when most plants were at the early jointing stage (Feekes 4) and the susceptible check had 5-10% severity of stripe rust, and sprayed again at the same rate on 22 Jun (15 days after the first application) when the plants were at the late jointing stage (Feekes 8-9) and stripe rust reached 40-60% 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 8 Jun at the tillering stage, 20 Jun at the jointing stage, 5 Jul at the flowering, and 18 Jul at the soft dough stage 1, 13, 28, and 41 days after the first fungicide application. Plots were harvested on 23 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 AvS in late May when plants were at the early tillering stage (Feekes 2). The disease reached 90-95% severity in the non-sprayed susceptible check plots on 5 Jul at the flowering stage, 31 days after the first fungicide application, and 100% on 18 Jul at the soft dough stage in the plots of the susceptible check without fungicide application. The two applications of Quilt at 14 fl oz/A completely controlled stripe rust. The fungicide applications significantly reduced the rAUDPC for the susceptible check and the commercially grown cultivars, except cultivars Expresso and JD that were highly resistant to stripe rust. The fungicide applications significantly increased grain test weight of the susceptible check (AvS), but not of any of the commercially grown cultivars. The fungicide applications significantly increased the grain yields of the susceptible check and eight of the commercially grown cultivars (Babe, Alpowa, Jefferson, WB-1035CL+, Nick, Whit, WB Fuzion, and Louise), and the increases ranged from 14.9 to 40. 9 bu/A (17.8-119.8%), whereas the seven remaining cultivars (Kelse, Solano, Buck Pronto, Expresso, Glee, Diva, and JD) did not have significant yield increases by the fungicide applications. Based on the yield data of the non-sprayed and sprayed plots, stripe rust caused yield loss of 40.9 bu/A (54.5%) for the susceptible check and losses of -2.5 to 41.4 bu/