Evaluation of foliar fungicides for control of stripe rust on winter wheat in 2018

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

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2019
Publication Date: 2/11/2019
Citation: Chen, X., Sprott, J.A., Evans, C.K., Liu, Y. 2019. Evaluation of foliar fungicides for control of stripe rust on winter wheat in 2018. Plant Disease Management Reports. 13:CF068.

Interpretive Summary: Fungicide application is an essential component for integrated management of stripe rust in winter wheat. In this study, 31 foliar fungicide treatments were evaluated for their efficacy in control of stripe rust on a susceptible winter wheat variety in a field near Pullman, Washington during the 2017-2018 crop season using a randomized complete block design with four replications for each treatment plus a non-treated chech. Fungicide application was made at the early jointing stage and/or flag-leaf stage with different rates depending upon the treatments. Disease severity was assessed four 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 natural stripe rust epidemic in 2018, all fungicide treatments significantly reduced rAUDPC, except one treatment of an early application. Significant differences in test weight were observed in 22 of the 31 treatments. Twenty four treatments significantly increased yield compared with the non-treated check, and the significant increases ranged from 18 bushes (48%) to 79 bushes (209%). The results can be used to choose fungicide treatments for more effective control of stripe rust when the disease has potential to cause significant yield losses on susceptible varieties.

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 30 Oct 17. Urea 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, Starane Flex, 13.5 fl oz/A, and M-90, 10.4 fl oz/A) were applied to the entire field to control weeds on 23 Apr 18 when wheat plants were at the early jointing stage (Feekes 3). Before the first fungicide application, the field was divided into individual plots of 4.5 ft (4 rows) in width and 15.2 to 17.2 ft in length by eliminating plants between plots by spraying herbicide (Glystar, 88.7 ml/gal plus M-90 0.25% v/v). 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 8 May when stripe rust was 0 to 0.1% severity in every plot. The second application timing at the flag-leaf stage (Feekes 8) was conducted on 23 May when stripe rust in the plots without first fungicide application reached 1-5% 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 8 May, 22 May, 4 Jun, and 19 Jun or 0, 14, 27, and 42 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 four 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 early May when plants were at the early jointing stage (Feekes 5) and reached 100% severity in middle Jun at the milk stage, in the non-treated check plots. The rAUDPC values of all treatments were significantly less than the non-treated check, except the treatment of Fortix 2.5 fl oz/A applied at Feekes 5. Twelve treatments (Tilt 4.0 fl oz/A, F4412 5.5 fl oz/A, Trivapro 13.7 fl oz/A, F4412 7.0 fl oz/A, Topguard EQ 7.0 fl oz/A, A15457 4.11 fl oz/A + A12705 6.02 fl oz/A + A7420 6.84 fl oz/A, A1547 4.11 fl oz/A + A12705 6.02 fl oz/A + A9898 5.5 fl oz/A, and Prosaro 6.5 fl oz/A at Feekes 8 and Tilt 4.0 fl oz/A at Feekes 5 followed by Tilt 4.0 fl oz/A at Feekes 8, Tilt 4.0 fl oz/A at Feekes 5 followed by Quilt Xcel 14.0 fl oz/A at Feekes 8, Topguard EQ 7.0 fl oz/A at Feekes 5 followed by Topguard 7.0 fl oz/A at Feekes 8, and Quilt Xcel 7.0 fl oz/A at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 8) provided the best control of stripe rust. Except the treatment of Fortix 2.5 fl oz/A at Feekes 5 followed by Fortix 2.5 fl oz/A at Feekes 8, all treatments of fungicides applied at either only Feekes 8 or both Feekes 5 and Feekes 8 had significantly greater test weight than the non-treated check. The test weights of all eight treatments applied only at Feekes 5 were not significantly different from the non-treated check. All treatments of either only a Feekes 8 application or both Feekes 5 and Feekes 8 applications significantly increased yield compared with the non-treated check. Except Zolera FX 2.5 fl oz/A, all treatments of only application at Feekes 5 did not increase yield compared with the non-treated check. The significant yield increases ranged from 18.1 bu/A (48%) by the treatment of Zolera FX 2.