Evaluation of foliar fungicides for control of stripe rust on winter wheat in 2023

Authors: Chen, Xianming; Evans, Conrad

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2024
Publication Date: 3/12/2024
Citation: Chen, X., Evans, C.K. 2024. Evaluation of foliar fungicides for control of stripe rust on winter wheat in 2023. Plant Disease Management Reports. 18. Article CF069.

Interpretive Summary: Fungicides are needed for control of 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 winter wheat. The field was planted with susceptible variety 'PS 279' in the fall of 2022 and divided into plots in spring 2023, and plants were inoculated on 10 April with spores of the wheat stripe rust pathogen collected from the same location in 2022. The first fungicide application timing at the early jointing stage was made on 25 May 2023 when stripe rust was just appearing, and the second application timing at the boot stage was conducted on 6 Jun when stripe rust was 30-35% severity in non-spray plots. Rust severity was assessed for each plot five times from 18 May to 20 June. Grain yield and test weight were measured at the harvest. Rust severity, test weight, and yield data were analyzed. All treatment significantly reduced overall stripe rust severity with 16 treatments (applied the first or first and second timings) provided better control of stripe rust than the three treatments with only the second timing. All treatments had significantly higher test weight than the non-treated check. All treatments produced yield higher than the non-treated check with the treatment of a new formulation applied twice at 16.0 fl oz/A producing the highest yield. The significant yield increases by the fungicide treatments ranged from 23.5 bu/A (26.2%) to 50.3 bu/A (43.2%). The results can be used for registering the new fungcide and select fungicides and timings for reducing wheat yield losses by stripe rust.

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 19 Oct 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 20 Apr 23 when plants at the late tillering stage (Feekes 3). The wheat plants in the spread rows surrounding the plots were inoculated on 10 Apr (Feekes 2-3) with urediniospores collected from the same farm in 2022. 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 12 May 23 when wheat plants were at the early jointing stage (Feekes 4-5). Before the first fungicide application, the field was divided into individual plots of 4.5-ft (4 rows) in width and 15.0 to 18.9-ft in length by eliminating plants between plots by spraying herbicide (Glystar 5 Extra, 24.0 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 25 May when stripe rust was just appearing (0.1-2.0% severity). The second application at the boot stage (Feekes 10) was conducted on 6 Jun when stripe rust was 30-35% 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. Rust severity (percentage of infected foliage per whole plot) was assessed for each plot on 18 May, 24 May, 5 Jun, 15 Jun, and 20 Jun, or 7 days and 1 day before and 11, 21, and 26 days after the first fungicide application timing, respectively. Plots were harvested on 2 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 from inoculation and possibly additional natural infection was observed as 0.1% severity in most of the plots on 18 May 23, 7 days before the first fungicide application, and reached 90-99% severity at the soft dough stage in the non-treated check by 20 Jun. The rAUDPC values of all fungicide treatments were significantly less than the non-treated check. All 16 treatments with the first or first and second applications provided better control of stripe rust than the three treatments with only the second application. All treatments had significantly higher test weight than the non-treated check, with the treatment of Aprovia Ace, 9.4 fl oz/A applied at both Feekes stages 5 and 10 having the highest test weight (62.0 lb/bu). All treatments produced yield higher than the non-treated check with the treatment of ADM.03509.F.3.B, 16.0 fl oz/A applied at both Feekes 5 and 10 producing the highest yield. The significant yield responses ranged from 23.5 bu/A (26.2%) by the treatment of Tilt 3.6EC, 4.0 fl oz/A at Feekes 5 to 50.3 bu/A (43.2%) by the treatment of ADM.03509.F.3.B, 16.0 fl oz/A applied at both Feekes stages 5 and 10.