Evaluation of foliar fungicides for control of stripe rust on spring wheat in 2022

Authors: Chen, Xianming; Evans, Conrad; Sprott, Jason

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2023
Publication Date: 3/15/2023
Citation: Chen, X., Evans, C.K., Sprott, J.A. 2023. Evaluation of foliar fungicides for control of stripe rust on spring wheat in 2022. Plant Disease Management Reports. 17. Article CF034.

Interpretive Summary: Foliar fungicide application is a major approach to reduce yield loss of wheat caused by stripe rust. A randomized complete block design experiment with four replications was conducted in a field near Pullman, Washington to determine efficacy of 19 fungicide treatments on control of stripe rust on a susceptible spring wheat variety (AvS). The field was planted on 23 April 2022, and plants were inoculated with spores of the wheat stripe rust pathogen collected from a winter wheat field at the same location in 2022. The first fungicide application timing at the early jointing stage was made on 15 June when stripe rust was just appearing (0.1% severity) in majority of the plots, and the second application timing at the boot stage was conducted on 1 Jul when stripe rust was 5-25% severity in unsprayed plots. Disease severity was assessed for each plot five times from 15 Jun to 22 July. Grain yield and test weight were measured at the harvest. Rust severity, test weight, and yield data were analyzed. All fungicide treatments significantly reduced the overal stripe rust value compared to the non-treated check, and four of them reduced stripe rust value to below 10%. Seventeen treatments had higher test weight than the non-treated check. All treatments produced grain yields higher than the non-treated check. The significant yield responses of the fungicide treatments ranged from 21.5 to 51.2 bushels per acre or 51.9 to 115.5% more grain. These results are useful for control of stripe rust on spring wheat using effective foliar fungicdes when needed.

Technical Abstract: The study was conducted in a field with Palouse silt loam soil near Pullman, WA. Stripe rust susceptible 'AvS' spring wheat was seeded in rows spaced 14-in. apart at 60 lb/A (99% germination rate) with a drill planter on 23 Apr 22. Urea fertilizer (46-0-0) was applied at the rate of 100 lb/A at the time of planting and at the same rate on 17 May when plants at the middle tillering stage (Feekes 2). The wheat plants in the spread rows surrounding the plots were inoculated on 26 May (Feekes 3) with fresh urediniospores collected from an experimental winter wheat field that was inoculated using urediniospores collected from the same farm in 2021. The field was divided into individual plots of 4.5-ft (4 rows) in width and 15.1 to 17.0-ft in length by eliminating plants between plots by spraying herbicide (Glystar 5 Extra, 35.5 ml/gal plus M-90 0.25% v/v) on 7 Jun 22, and herbicides (Huskie, 15 fl oz/A, Axial Star, 16.4 fl oz/A, and M-90, 10.4 fl oz/A) were applied to the entire field to control weeds on 9 Jun 22 when wheat plants were at the early jointing stage (Feekes 4). 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 15 Jun when stripe rust was just appearing (0.1% severity) in majority of the plots. The second application at the boot stage (Feekes 10) was conducted on 1 Jul when stripe rust was 5-25% severity in unsprayed plots. 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 for each plot on 15 Jun, 30 Jun, 8 Jul, 15 Jul, and 22 Jul or 0 day before and 15, 23, 30, and 37 days after the first fungicide application timing, respectively. Plots were harvested on 25 Aug when kernels had 13 to 15% 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 was observed as 0.1% severity in majority of the plots on 15 Jun 22, 20 days after inoculation, the same day of the first fungicide application, and reached 90-100% severity at the soft dough stage in the non-treated check plots by 22 Jul. The rAUDPC values of all fungicide treatments were significantly less than the non-treated check. Four treatments (Trivapro 7.0 fl oz/A at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 10, Tilt 4 fl oz/A at Feekes 5 followed by Quilt Xcel 14.0 fl oz/A at Feekes 10, Miravis Ace 7.0 fl oz/A at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 10, and Quilt Xcel 14.0 fl oz/A at Feekes 10) reduced rAUDPC to below 10%. Except two treatments (Manzate Max 51.2 fl oz/A at Feekes 10 and Tilt 4 fl oz/A at Feekes 5), all treatments had higher test weight than the non-treated check. All treatments produced yield higher than the non-treated check. The significant yield responses ranged from 21.5 bu/A (51.9%) by the treatment of Manzate Max 51.2 fl oz/A at Feekes 10 to 46.7 bu/A (115.5%) by the treatment of ADM.03509.F.3.D 22.0 fl oz/A at Feekes 10.