Control of stripe rust of spring 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 spring wheat with foliar fungicides in 2016. Plant Disease Management Reports. 11:CF022.

Interpretive Summary: Stripe rust of wheat is an important disease of spring wheat. Fungicides are needed to reduce damage when a stripe rust epidemic is developing. In this study, 47 foliar fungicide treatments were tested for efficacy in control of stripe rust during the 2016 crop season using a randomized complete block design with four replications for each treatment plus a non-treated chech. A susceptible wheat variety was planted in a field near Pullman, WA in the spring. Fungicides were applied twice at early jointing stage and/or flag leaf stage depending upon the treatments. Disease severity was assessed five times during the rust season, and the data were used to calculate values of area under the disease progress curve (AUDPC) and relative AUDPC (rAUDPC). Under the severe epidemic, all fungicide treatments with the first application significantly reduced rust severity at the boot stage. The rAUDPC values of all treatments were significantly less than the non-treated check, except one treatment. Significant differences in grain test weight were observed among the fungicide treatments, and the test weights from treatments with the later application were significantly higher than that of the non-treated check, except few treatments. Most treatments significantly increased grain yield compared with the non-treated check, and the significant increases of grain yield ranged from 8 bushes (65%) to 56 bushes (449%). 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 ‘Avocet S’ spring wheat was seeded in rows spaced 14-in. apart at 60 lb/A (99% germination rate) with a drill planter on 4 May 2016. Urea fertilizer (46-0-0) was applied at the rate of 100 lb/A on 27 May when wheat plants were at the tillering stage (Feekes 2). 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 31 May when wheat plants were at the tillering stage 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 16.8 ft in length by eliminating plants between plots by spraying herbicide (Glystar, 3.4 fl oz/gal + M90 3.4 fl oz/gal) on 6 Jun. 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 4) was made on 7 Jun when stripe rust was 2 to 10% severity in the field. The second application was done at the flag leaf stage (Feekes 8) on 22 Jun when stripe rust in the plots without first fungicide application reached 40-50% severity. The third application was done at the boot stage (Feekes 10.) on 1 Jul when stripe rust in the plots without previous fungicide applications reached 90-95% 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 8 Jun, 15 Jun, 30 Jun, 10 Jul (data not presented), and 18 Jul or 1, 8, 23, 33, and 41 days after the first fungicide application timing, respectively. Plots were harvested on 22 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 May when plants were at the tillering stage (Feekes 2-3) and reached 90% and 100% severity at the flowering and milk stages, respectively in the non-treated check plots. All fungicide treatments with 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 milk (data not presented) and soft dough stages. 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. Four treatments, Trivapro 9.4 fl oz/A applied at Feekes 4 followed by Trivapro 13.7 fl oz/A at Feekes 8, Quilt Xcel 7.0 fl oz/A at Feekes 4 followed by Trivapro 13.7 fl oz/A at Feekes 8, Trivapro 9.4 fl oz/A applied at Feekes 4 followed by Quilt Xcel 10.5 fl oz/A at Feekes 8, and Quilt Xcel 7.0 fl oz applied at Feekes 4 followed by Quilt Xcel 10.5 fl oz/A at Feekes 8, provided the best control of stripe rust and also produced the highest yields. Significant differences in grain test weight were observed among the fungicide treatments. The test weights from treatments of only the first application were similar to that of non-treated check; and those of treatments with the later application were significantly higher than that of the non-treated check, except treatments of OR 009F-1-A or OR 097F-3 at vario