Evaluation of foliar fungicides for control of stripe rust on winter 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 winter wheat in 2022. Plant Disease Management Reports. 17. Article CF035.

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 winter wheat variety (PS 279). The field was planted on 2 November 2021 and divided into plots in spring 2022, and plants were inoculated with spores of the wheat stripe rust pathogen collected from the same location in 2021. The first fungicide application timing at the early jointing stage was made on 10 May 2022 when stripe rust was just appearing (0.1% severity) in some of the plots, and the second application timing at the late tillering stage was conducted on 1 Jun when stripe rust was 1-10% severity in unsprayed plots. Disease severity was assessed for each plot six times from 10 May to 5 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 two of them provided the best control of stripe rust. Three 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 10.0 to 55.1 bushels per acre or 85.7 to 469.6% more grain. These results are useful for control of stripe rust 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 'PS 279' winter wheat was seeded in rows spaced 14-in. apart at 60 lb/A (99% germination rate) with a drill planter on 2 Nov 21. 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 7 Apr 22 when plants at the late tillering stage (Feekes 3). The wheat plants in the spread rows surrounding the plots were inoculated on 21 Mar (Feekes 2), 3 Apr (Feekes 3), and 29 Apr (Feekes 4) with urediniospores collected from the same farm in 2021. 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 11 May 22 when wheat plants were at the early jointing stage (Feekes 5). Before the first fungicide application, 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). 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 10 May when stripe rust was just appearing (0.1% severity) in 7 of the 80 plots. The second application at the late jointing stage (Feekes 8) was conducted on 1 Jun when stripe rust was 1-10% 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 10 May, 31 May, 14 Jun, 21 Jun, 28 Jun, and 5 Jul or 0 day before and 21, 35, 42, and 49 days after the first fungicide application timing, respectively. Plots were harvested on 23 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 six 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 some of the plots on 10 May 22, the same day of the first fungicide application, and reached 100% severity at the flowering stage in the non-treated check and some treated plots by 28 Jun. The rAUDPC values of all fungicide treatments were significantly less than the non-treated check. Two treatments (Trivapro 7.0 fl oz/A at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 8 and Prosaro 8.2 fl oz/A at Feekes 8) provided the best control of stripe rust. However, none of the treatments provided 100% protection as the relatively early inoculation and stripe rust favorable wet and cool weather conditions allowed the disease lasting long, resulting in the generally low yields in the experimental field. Three treatments (Miravis Ace 7.0 fl oz/A followed by Trivapro 2.2SE 13.7 fl oz/A, Trivapro 7.0 fl oz/A at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 8, and Prosaro 8.2 fl oz/A at Feekes 8) had higher test weight than the non-treated check. All treatments produced yield higher than the non-treated check with the treatment of Prosaro 8.2 fl oz/A at Feekes 8 producing the highest yield. The significant yield responses ranged from 10.0 bu/A (85.7%) by the treatment of Tilt 3.6EC, 4.0 fl oz/A at Feekes 5 to 55.1 bu/A (469.6%) by the treatment of Prosaro 421SC 8.2 fl oz/A at Feekes 8.