Control of stripe rust of winter wheat with various foliar fungicides, 2014

Authors: Chen, Xianming; Evans, Conrad; LIU, YUMEI - Washington State University; Cox-Heath, Marie

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2014
Publication Date: 3/20/2014
Citation: Chen, X., Evans, C.K., Liu, Y., Cox-Heath, M.E. 2014. Control of stripe rust of winter wheat with various foliar fungicides, 2014. Plant Disease Management Reports. 9:CF021.

Interpretive Summary: Fungicide application is often needed to control stripe rust. In this study, 21 foliar fungicide treatments were tested for efficacy in control of stripe rust on winter wheat during the 2013-2014 crop season using a randomized complete block design with four replications for each treatment plus a non-treated chech. The experimental field near Pullman, WA was planted with a susceptible winter wheat variety on October 18, 2013. Fungicides were applied at early jointing stage and/or late jointing stage depending upon the treatments. Disease severity was assessed five times during the stripe rust development created by inoculating the field with a mixture of two locally predominant races of the pathogen. Area under the disease progress curve (AUDPC) was calculated for each plot using the five sets of severity data. Relative AUDPC was calculated as percentage of the non-treated check. Grain yield and test weight were measured. Rust severity, relative AUDPC, test weight, and yield data were subjected to analysis of variance and means were compared to determine the difference among the treatments. Stripe rust reached 100% severity at milk stage, allowing adequate evaluation of fungicide efficacy. All fungicide treatments significantly reduced rust AUDPC. All treatments, except one, increased test weight. Twenty treatments significantly increased grain yield compared to the non-treated check, and the increases ranged from 24.68 to 54.30%. 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 near Pullman, WA. Fertilizer (Osmocota 14-14-14) was applied at 60 lb/A at the time of cultivation on 18 Oct 2013. 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 18 Oct 2013. Nitrogen fertilizer (46-0-0, 125 lb/A) and herbicides (Huskie, 15 fl oz/A, Axial, 80 ml/A, and M-90, 140 ml/A) were applied on 8 May 2014 when wheat plants were at the early jointing stage. The field was inoculated with a mixture of urediniospores of locally predominant races PSTv-14 and PSTv-37 of Puccinia striiformis f. sp. tritici on 16 Apr 2014 when plants were at the late tillering stage (Feekes 3). Before the first fungicide application, the field was divided into individual plots of 4.5 ft (4 rows) in width and 11.5 to 16.5 ft in length by eliminating plants between plots with a rototiller. 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 13 May when stripe rust was 0 to 2% severity in the field. The second application was done at the late jointing stage (Feekes 8) on 30 May when stripe rust in the plots without first fungicide application reached 5 to 15% 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. A randomized block design was used with four replications. Disease severity (percentage of diseased foliage per whole plot) was assessed from each plot on 27 May, 10 Jun, 24 Jun, 3 Jul (data not shown), and 14 Jul or 14, 28, 42, 51, and 62 days after the first fungicide application timing, respectively. Plots were harvested on 6 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 control. Rust severity, rAUDPC, test weight, and yield data were subjected to analysis of variance and means were separated by Fisher’s protected LSD test. The first fungicide was applied as stripe rust began to develop (Feekes 5) and the second application as the disease reached 5 to 15% severity (Feekes 8) in the plots without the first application. Stripe rust reached 100% severity in the nontreated check plots approximately 78 days after inoculation or 51 days after the first application. Stripe rust developed slowly as the weather was hot and dry in June and July. All fungicide treatments significantly reduced rust severity compared to the nontreated at the flowering stage (Feekes 10.5). The rAUDPC values of all treatments were significantly less than the nontreated. Among all treatments, the treatment of Aproach 3.0 fl oz/A at Feekes 5 followed by Aproach 6.8 fl oz/A at Feekes 10 provided the best disease control, but all other treatments had similar control, except the three treatments with Equation and the treatment with Quadris 8.0 fl oz at Feekes 8. All treatments, except Quadris 8.0 fl oz/A at Feekes 8, significantly increased test weight compared to the nontreated. The treatment of A15457 2.74 fl oz/A + Tilt 2.72 fl oz/A + Quadris 4.1 fl oz/A at Feekes 5 followed by Quilt Xcel 10.5 fl oz/A at Feekes 8 produced the highest test weight, and the test weights of all other treatments, except the treatments of Equation 4.0 fl oz, Equation 8.0 fl oz, and Quadris 8.0 fl oz at Feekes 8, were not significantly different from one another. Except the treatment of CHA-073 10.5 fl oz, all treatments significantly increased yield compared with the nontreated, and the significant increases ranged from 24.68% by the treatment of Equation 16.0 fl oz/A at Feekes 8 to 54.30% by the tre