|LIU, YUMEI - Washington State University|
Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2016
Publication Date: 3/7/2016
Citation: Chen, X., Evans, C.K., Liu, Y. 2016. Responses of winter wheat cultivars to fungicide application for control of stripe rust in 2015. Plant Disease Management Reports. 10:C023.
Interpretive Summary: Wheat stripe rust is primarily controlled by growing resistant cultivars and secondarily by fungicides. To determine cultivar responses to fungicide application, 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 during the 2014-2015 growth season. Stripe rust severity was assessed from each plot four times and grain test weight and yield were measured for each plot of fungicide sprayed and no-sprayed treatments of each cultivar. Area under disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. The fungicide application significantly reduced rAUDPC for the susceptible check and only four cultivars, but not significantly increased the test weight for any cultivars. The fungicide application increased yield by 1.05 to 28.81 bu/A in 18 cultivars, but only significant for the susceptible check. For six cultivars that have high levels of resistance, the fungicide application even reduced yield, but none of the yield reductions was significant. Stripe rust caused yield losses from -5.85 to 28.81 bu/A (-4.45 to 27.63%) with a mean of 5.31 bu/A (3.86%), and fungicide application increased yield by -4.26 to 38.18% with a mean of 4.02%. The information is useful for managing the disease by fungicide application based on indivivual cultivars.
Technical Abstract: To determine the responses of winter wheat cultivars with various levels of stripe rust resistance grown in the U.S. Pacific Northwest to fungicide application for control of stripe rust, this study was conducted in a field near Pullman, WA. Urea (46N-0P-0K) 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 2014 or new releases. These genotype and cultivars were seeded in rows spaced 14 in. apart at 60 lb/A (99% germination rate) with a drill planter on 17 Oct 14. The plots were 4.5 ft in width and 13.0 to17.0 ft in length. Urea (46N-0P-0K) at 100 lb/A was applied on 1 May 15 at the early stage (Feekes 4-5) and herbicide (Huskie 15.0 fl oz/A + Axial XL 16.4 fl oz/A + M-90 10.4 fl oz/A) was applied on 7 May when wheat plants were at the early jointing stage (Feekes 5). Fungicide Quilt 1.66 SE was sprayed at the rate of 11.0 fl oz/A mixed with M-90 at the rate of 1% v/v in 16 gallon water/A on 6 May when most plants at early jointing stage (Feekes 5) and stripe rust appeared in the spreader rows of PS 279 surrounding the 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. A randomized complete block design was employed with a split block based on spray or not spray and with four replications. Disease severity (percentage of diseased foliage per whole plot) was assessed from each plot on 6 May at early jointing stage, 26 May at heading stage, 12 Jun at milk stage, and 27 Jun at soft dough stage or 0, 20, 37, and 52 days after the fungicide application. Plots were harvested on 5 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. Stripe rust of natural infection was first observed in the spreader rows of PS 279 surrounding the field on 28 Apr 15, about two weeks earlier than normal for the area. The disease reached 5-30% severity in the non-sprayed susceptible check plots on 26 May (heading stage), 20 days after the fungicide was applied, and 100% on 12 Jun (milk stage) in the plots of the susceptible check without fungicide application. The one time and early application protected the wheat about one month, but did not provide an adequate control for the susceptible check as stripe rust developed to 80-90% severity in the PS 279 plots applied with the fungicide. The fungicide application significantly reduced rAUDPC for the susceptible check, but the reduction was only 24.78%. The fungicide application was also significantly reduced rAUDPC for cultivars Xerpha, Tubbs 06, Mary, and ORCL-103, but the reductions was not significant for the remaining 19 cultivars with higher levels of resistance as rust severity was low in both no-sprayed and sprayed plots. For test weight, none of the cultivars, including the susceptible check, had significant increase by the fungicide application. The fungicide application increased yield by 1.05 to 28.81 bu/A in 18 cultivars, but only significant for the susceptible check. For other 6 cultivars (ARS-Amber, Cara, Madsen, Otto, Skiles, and Norwest 553), which have high levels of resistance to stripe rust, the fungicide application reduced yield, but none of the yield reductions was significant. Based on the yield data of the no-sprayed and sprayed plots, stripe rust caused yield losses from -5.85 to