|LIU, YUMEI - Washington State University|
Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2015
Publication Date: 3/20/2015
Citation: Chen, X., Evans, C.K., Liu, Y., Cox-Heath, M.E. 2015. Effects of fungicide application on control of stripe rust on winter wheat cultivars in 2014. Plant Disease Management Reports. 9:CF018.
Interpretive Summary: Wheat stripe rust is primarily controlled by growing resistant cultivars, but not all currently grown cultivars have an adequate level of resistance. To determine the effects of fungicide application on winter wheat cultivars under stripe rust epidemic, 23 cultivars of winter wheat widely grown in the U.S. Pacific Northwest plus a susceptible check were tested in a field near Pullman, WA during the 2013-2014 growth season using a randomized split-block design with four replications. The field was inoculated with a mixture of locally predominant races of the stripe rust pathogen. Stripe rust severity was assessed from each plot three times and grain test weight and yield were measured for each plot of no-spray and fungicide spray treatments of each cultivar. Area under disease progress curve (AUDPC) was calculated for each plot using the three sets of severity data. 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. The one time application at the early stage of disease development protected the crops throughout the late growing season. The fungicide application significantly reduced rAUDPC for 12 cultivars, significantly increased test weight in nine cultivars, and significantly increased grain yield in five cultivars including the susceptible check. Stripe rust caused yield losses from -3.8 to 33.2 bu/A (-4.6 to 55.8%), and fungicide application increased yield by -4.4 to 126.4%. The data can be used to control stripe rust based on individual cultivars.
Technical Abstract: To determine the effects of fungicide application on control of stripe rust on individual winter wheat cultivars with various levels of resistance grown in the U.S. Pacific Northwest, this study was conducted in a field near Pullman, WA. Fertilizer (100N-20K-25S) was applied at 80 lb/A at the time of cultivation on 10 Oct 13. 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 2013 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 10 Oct 13. The plots were 4.5 ft in width and 14.3-16.3 ft in length. Because a low level of stripe rust was predicted for the 2014 growth season, the field was inoculated with a mixture of locally predominant races PSTv-14 and PSTv-37 of Puccinia striiformis f. sp. tritici on 16 Apr 14 at late tillering stage (Feekes 3). Urea (46N-0P-0K) at 125 lb/A was applied on 28 Apr 14 at the early stage (Feekes 4) and herbicide (Allecto, 24 fl oz/A mixed with surfactant M-90, 140 ml/A) was applied on 12 May when wheat plants were at the early jointing stage (Feekes 5). Fungicide Quilt 1.66 SE was sprayed at the rate of 14.0 fl oz/A mixed with M-90 at the rate of 1% v/v in 16 gallon water/A on 29 May when most plants at boot-heading stage and stripe rust reached 10% severity on the susceptible check PS 279. 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 split-block design was used with four replications. Disease severity (percentage of diseased foliage per whole plot) was assessed from each plot on 27 May at boot stage, 10 Jun at flowering stage, and 24 Jun at soft dough stage or two days before the fungicide application and 12 and 26 days after application. Plots were harvested on 6 Aug when kernels had 3-5% 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 was first observed in the field on May 7, three weeks after the inoculation. The disease was developing slowly due to the dry and hot weather conditions. The disease reached 10% severity on the susceptible check on 27 May, two days before the fungicide was applied and 90% on 10 Jun (flowering stage) and 100% on 24 Jun (soft dough stage) in the plots of the susceptible check without fungicide application. The one time application protected the crops throughout the late growing season as no obvious re-development of stripe rust in the sprayed plots up to the soft dough stage. The fungicide application significantly reduced rAUDPC for cultivars Eltan, Tubbs 06, ORCF-102, ARS-Amber, ARS-Crystal, Mary, Bauermeister, Stephens, Puma, and ORCF-103, as well as the susceptible check PS 279, but the reduction was not significant for the remaining 11 cultivars. For test weight, nine cultivars (PS 279, Eltan, Xerpha, Tubbs 06, ORCF-102, ARS-Crystal, Mary, Bauermeister, and ORCF-103) had significant increase in sprayed plots compared to the no-sprayed plots, and the significant increases ranged from 1.48 to 7.72 lb/bu. The fungicide application significantly increased grain yield for four of the commercially grown cultivars (Eltan, Xerpha, Tubbs 06, and ORCF-102) and the susceptible check. The significant increases ranged from 18.39 to 33.20 bu/A, or 25.60 to 126.43%. Based on the yield data of the no-sprayed and sprayed plots, stripe ru