Control of stripe rust of winter wheat with foliar fungicides in 2016

Authors: Chen, Xianming; Evans, Conrad; Sprott, Jason; LIU, YUMEI - Washington State University

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. Control of stripe rust of winter wheat with foliar fungicides in 2016. Plant Disease Management Reports. 11:CF016.

Interpretive Summary: Stripe rust of wheat is preferrably controlled by developing and growing resistant cultivars, but resistant cultivars can become susceptible or the resistance is not adequate. Fungicide application is needed to reduce yield loss. In this study, 23 foliar fungicide treatments were tested for efficacy in control of stripe rust during the 2015-2016 crop season using a randomized complete block design with four replications for each treatment plus a non-treated chech. Fungicides were applied twice at early jointing stage and/or boot stage depending upon the treatments. Disease severity was assessed five times during the stripe rust development of natural infection, and the data were used to calculate values of area under the disease progress curve (AUDPC) and relative AUDPC (rAUDPC). Grain yield and test weight were measured. Under the severe epidemic, all fungicide treatments of the first application significantly reduced rust severity at the boot stage; and all treatments with only the first application did not significantly reduce rust severity at the flowering stage, except one treatment. Except one treatment, all fungicide treatments significantly reduced rAUDPC. Significant differences in test weight were observed among the fungicide treatments. Except one treatment, all treatments significantly increased yield compared with the non-treated check, and the significant increases ranged from 19 bushes (164%) to 91 bushes (797%). The results can be used for registering new fungicides and for control of stripe rust.

Technical Abstract: The study was conducted in a field with Palouse silt loam soil near Pullman, WA. Stripe rust susceptible ‘PS 279’ winter wheat was seeded in rows spaced 14-in. apart at 60 lb/A (99% germination rate) with a drill planter on 12 Oct 2015. Ammonia fertilizer (46-0-0) was applied at the rate of 100 lb/A at the time of planting. Herbicides (Huskie, 15 fl oz/A, Axial XL, 16.4 fl oz/A, and M-90, 10.4 fl oz/A) were applied to the entire field to control weeds on 22 Apr when wheat plants were at the early jointing stage (Feekes 4). Before the first fungicide application, the field was divided into individual plots of 4.5 ft (4 rows) in width and 15.3 to 16.6 ft in length by eliminating plants between plots by spraying herbicide (Alecto, 24 fl oz/A) on 5 May. Fungicides were applied in 16 gal water/A on different dates and stages depending upon the treatment. The first fungicide application timing at the early jointing stage (Feekes 5) was made on 10 May when stripe rust was 2 to 5% severity in the field. The second application was done at the boot stage (Feekes 10) on 24 May when stripe rust in the plots without first fungicide application reached 80% severity. The third application was done at the heading stage (Feekes 10.2) on 31 May when stripe rust in the plots without previous fungicide applications reached 95% severity. A 601C backpack sprayer was used with a CO2-pressurized spray boom at 18 psi having three operating 0.25-in. nozzles spaced 19-in. apart. A randomized complete block design was used with four replications. Disease severity (percentage of diseased foliage per whole plot) was assessed from each plot on 10 May, 23 May, 6 Jun, 15 Jun (data not presented), and 29 Jun or 0, 13, 27, 36, and 50 days after the first fungicide application timing, respectively. Plots were harvested on 15 Aug when kernels had 3 to 5% kernel moisture and test weight of kernels was measured. Area under disease progress curve (AUDPC) was calculated for each plot using the five sets of severity data. Relative AUDPC (rAUDPC) was calculated as percent of the non-treated check. Rust severity, rAUDPC, test weight, and yield data were subjected to analysis of variance and means were separated by Fisher’s protected LSD test. Stripe rust from natural infection started developing in the plots in late April when plants were at the early jointing stage (Feekes 4) and reached 80% and 100% severity at the boot and flowering stages, respectively in the non-treated check plots. All fungicide treatments of the first application significantly reduced rust severity compared to the non-treated check and the treatments without the first application at the boot stage; and all treatments with only the first application did not significantly reduce rust severity compared to the non-treated check at the flowering stage, except the treatment of Trivapro 13.7 fl oz/A that did not significantly reduced rust severity at the milk stage (data not presented). The rAUDPC values of all treatments were significantly less than the non-treated check, except the treatment of A21573A 11.4 fl oz/A applied at Feekes 10.2. Three treatments, Trivapro 9.4 fl oz/A applied at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 10, Quilt Xcel 7.0 fl oz/A at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 10, and Trivapro 9.4 fl oz/A applied at Feekes 5 followed by Quilt Xcel 10.5 fl oz/A at Feekes 10, provided the best control of stripe rust. Significant differences in test weight were observed among the fungicide treatments. Treatments of only the first application had significantly low test weight compared to those with the later applications. The treatments that provided the best control of stripe rust did not significantly increase test weight compared to the untreated check, likely due to the fact that the small kernels increased density. Except the treatment of Preemptor 6.0