Control of stripe rust of spring 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 spring wheat with various foliar fungicides, 2014. Plant Disease Management Reports. 9:CF016.

Interpretive Summary: A total of 22 foliar fungicide treatments were evaluated for control of stripe rust on spring wheat during the 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 spring wheat variety on May 6. The field was inoculated with a mixture of locally predominant races of the stripe rust pathogen wheat plants were at tillering stage. Fungicides were applied at early jointing stage and/or boot stage depending upon the treatments. Disease severity was assessed five times during the crop season. 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 differences among the treatments. Stripe rust reached 100% severity at milk stage, allowing adequate evaluation of fungicide efficacy. All fungicide treatments significantly reduced rust AUDPC. None of the treatments significantly increased or decreased test weight compared to the non-treated check. Twenty of the 22 treatments significantly increased grain yield, and the significant increases ranged from 28 to 161%. The results can be used for registering new fungicides and for implementing chemical control of stripe rust when needed.

Technical Abstract: The study was conducted in a field with Palouse silt loam near Pullman, WA. Nitrogen fertilizer (46-0-0) was applied at 100 lb/A at the time of cultivation on 6 May 2014. Stripe rust susceptible ‘Lemhi’ spring wheat was seeded in rows spaced 14 in. apart at 80 lb/A (99% germination rate) with a drill planter on 6 May. Herbicides (Huskie, 15 fl oz/A, Axial, 80 ml/A, and M-90, 140 ml/A) were applied on 22 May when wheat plants were at the tillering stage (Feekes 2). 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 27 May when plants were at the tillering stage (Feekes 2). Before the first fungicide application, the field was divided into individual plots of 4.5 ft (4 rows) in width and 15.5 to 17.1 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 19 Jun when stripe rust was 3 to 5% severity in the field. The second application was done at the boot stage (Feekes 10) on 30 Jun when stripe rust in the plots without first fungicide application reached 15 to 20% 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 18 Jun, 1 Jul, 14 Jul, 21 Jul, and 6 Aug (data not shown) or one day before and 12, 25, 32, and 48 days after the first fungicide application timing, respectively. Plots were harvested on 29 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 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 at Feekes 5 as stripe rust began to develop (3 to 5% severity) and the second application as the disease reached 15 to 25% severity (Feekes 8) in the plots without the first application. Stripe rust reached 100% severity in the nontreated check plots approximately 55 days after inoculation or 32 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 Tilt 2.0 fl oz/A at Feekes 5 followed by Quilt Xcel 10.5 fl oz/A at Feekes 10 provided the best disease control, but four other treatments (Tilt 2.0 fl oz/A at Feekes 5 followed by Quilt Xcel 10.5 fl oz/A + A15457 4.1 fl oz/A at Feekes 10; 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 10; Aproach 3.0 fl oz/A at Feekes 5 followed by Aproach 6.8 fl oz/A at Feekes 10; and Aproach 3.0 fl oz/A + Tilt 4.0 fl oz/A at Feekes 5 followed by Aproach 6.0 fl oz/A + Tilt 4.0 fl oz/A at Feekes 10) had similar control. None of the treatments significantly increased or decreased test weight compared with the nontreated. All treatments, except Viathon 32 fl oz/A and CHA-073 14 fl oz/A at Feekes 10, 22 treatments, significantly increased the yield compared with the nontreated. The significant yield increases ranged from 28.42% (by the treatment of Equation 4.0 fl oz/A at Feekes 10) to 161.13% (by the treatment of A15457 2.74 fl oz/A + Tilt 2.72