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 spring wheat cultivars to fungicide application for control of stripe rust in 2018. Plant Disease Management Reports. 13:CF065.
Interpretive Summary: Fungicide application is needed to control stripe rust because not all spring wheat varieties have an adequate level of resistance when the disease is severe. To evaluate spring wheat varieties for responses to fungicide application, 23 spring wheat varieties widely grown in the U.S. Pacific Northwest plus a susceptible check were tested in a field near Pullman, WA in 2018. For the spray plots, fungicide, Quilt Xcel, was applied at the beginning of the rust season. 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 97% in the susceptible check and rust reduction was also signifcant in 18 of the 23 commercially grown varieties. The fungicide application significantly increased grain test weight of the susceptible check and seven 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 12 to 47 bu/A, whereas the 14 remaining varieties did not have significant yield diffences, indicating adequate resistance. Based on the yield data, stripe rust caused yield loss of 61 bu/A (66%) for the susceptible check and 12-47 bu/A (11-45%) for commercial varieties without adequate resistance. The results are valuable for managing stripe rust 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 application 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’ was used as a susceptible check, and 23 cultivars were selected based on their acreage planted in the state of Washington in 2017. 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 4 May 18. The plots were 4.5 ft in width and 14.1 to16.7 ft in length. Ammonium nitrogen fertilizer was applied at 100 lb/A on 14 May, ten days after planting. Herbicides (Huskie 15.0 fl oz/A + Axial XL 16.4 fl oz/A + Starane Flex 13.5 fl oz/A + M-90 10.4 fl oz/A) were applied on 2 Jun when wheat plants were at the early jointing stage (Feekes 5). On 8 Jun when most plants were at the jointing stage (Feekes 6), 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 Avocet S plants (1-5% 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 8 Jun at the jointing stage (Feekes 6), 26 Jun at the boot stage (Feekes 10), 11 Jul at the flowering stage (Feekes 10.5), and 20 Jul at the soft dough stage (Feekes 11.2) or 0, 18, 33, and 42 days after the fungicide application. Plots were harvested on 24 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 Avocet S plants in early Jun. The disease reached 100% severity in the non-sprayed susceptible check plots on 11 Jul (Feekes 10.5), 33 days after the fungicide application. The application of Quilt Xcel at 14 fl oz/A reduced rAUDPC by 97% in the susceptible check (Avocet S) plots. The fungicide application also significantly reduced rAUDPC of 18 commercial cultivars (Babe, WB6341, WB-1035CL+, SY605CL, Kelse, Whit, Louise, Solano, Tekoa, Alum, Glee, Buck Pronto, Melba, SY Steelhead, SY Selway, Express, Diva, and Chet). The fungicide application significantly protected grain test weight of the susceptible check (Avocet S) and seven cultivars (Babe, WB6341, WB-1035CL+, SY605CL, Kelse, Whit, and Louise) by 1.5 to 3.6 lb/bu. The fungicide applications made significant yield differences for the susceptible check (60.8 bu/A more in the sprayed plots) and nine commercial cultivars (Babe, WB6341, WB-1035CL+, SY605CL, Kelse, Whit, Louise, Solano, and Tekoa) with 12.4 to 46.9 bu/A more grain in the sprayed plots. The remaining 14 cultivars (Alum, Glee, Buck Pronto, Melba, SY Steelhead, SY Selway, Seahawk, Dayn, Express, Diva, Chet, WB9518, JD, and WB6121) showed adequate levels of stripe rust resistance and had insignificantly low or no reduction on yield. These data indicated that stripe rust caused yield loss of 60.8 bu/A (66.4%) on the susceptible check and 13.5% yield loss on average across the commercially grown cultivars. This study also indicated that 39% commercial cultivars needed fungicide application under the level of stripe rust epidemic in 2018.