Evaluation of Pacific Northwest spring wheat cultivars to fungicide application for control of stripe rust in 2021

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

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: Stripe rust is one of the most destructive diseases of spring wheat in the Pacific Northwest, and the disease is controlled by planting resistant varieties and applying fungicides if varieties do not have adequate resistance. This study was conducted to determine yield losses by stripe rust and responses to fungicide application for 23 spring wheat varieties widely grown in the U.S. Pacific Northwest plus a susceptible check in a field near Pullman, WA during the 2021 growth season. The field was dust-inoculated with the wheat stripe rust pathogen in the late jointing stage. For the spray plots, fungicide Quilt Xcel was applied at the early jointing stage and again at the boot stage. Stripe rust severity was recorded four times, and grain test weight and yield were measured for each plot at harvest. Area under the disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. AUDPC, test weight, and yield data were subjected to analysis of variance, and the effect of fungicide application on AUDPC, test weight, and yield was determined in comparison with non-sprayed plots for each cultivar by Fisher's protected LSD test. Despite the field was inoculated, stripe rust did not develop much due to the severe drought and hot conditions. No stripe rust was scored for the commercially grown cultivars. No significant differences in both test weight and yield between the sprayed and non-sprayed plots for all cultivars, including the susceptible check. The results showed that under severe drought and hot conditions, stripe rust could not develop and fungicide application could not make differences in test weight and yield on spring wheat.

Technical Abstract: This study was conducted in a field near Pullman, WA to evaluate the control of stripe rust with fungicide applications on major spring wheat cultivars grown in the U.S. Pacific Northwest and assess yield loss caused by the disease. Spring wheat genotype 'AvS' was used as a susceptible check, and 23 cultivars were selected based on their high acreage planted in the state of Washington in 2020. The 24 entries were arranged in a randomized split block design based on fungicide application, with four replications. They were seeded in rows spaced 14-in. apart at 60 lb/A (99% germination rate) with a drill planter on 20 Apr 21. The plots were 4.5-ft in width and 14.8 to 16.5-ft in length. Ammonium nitrogen fertilizer was applied at 100 lb/A at the time of planting and again on 17 May at the same rate when plants were at late tillering stage (Feekes 3). Herbicides (Huskie 15.0 fl oz/A + Axial XL 16.4 fl oz/A + M-90 10.4 fl oz/A) were applied on 2 Jun when wheat plants were at the early jointing stage (Feekes 5). On 2 Jun when most plants were at the early jointing stage (Feekes 5) and stripe rust was absent, Quilt Xcel 2.2SE was sprayed at the rate of 14.0 fl oz/A mixed with 0.25% v/v M-90 in 16-gallon water/A and sprayed again at the same rate on 16 Jun when plants were at the boot stage (Feekes 10) and stripe rust was still absent in the field. A 601C backpack sprayer was used with a CO2-pressurized spray boom at 18 psi having three operating ¼ in. nozzles spaced 19-in. apart. The field was dust-inoculated with urediniospores of a mixture of races of the wheat stripe rust pathogen from the same location in 2020 mixed with talc at the 1:20 ratio on 11 June (Feekes 8). Disease severity (percentage of stripe rust infected foliage per whole plot) was assessed from each plot on 1 Jun at the early jointing stage (Feekes 5), 15 Jun at the boot stage (Feekes 10), 29 Jun at the late flowering stage (Feekes 10.54), and 6 Jul at the soft-dough stage (Feekes 11.2) or 1 day before, 13, 27, and 34 days after the first time of the fungicide application, respectively. Plots were harvested on 20 Aug when kernels had 13 to 15% kernel moisture and test weight of kernels was measured. Area under the disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. AUDPC, test weight, and yield data were subjected to analysis of variance, and the effect of fungicide application on AUDPC, test weight, and yield was determined in comparison with non-sprayed plots for each cultivar by Fisher's protected LSD test. Despite the field was inoculated, stripe rust did not develop much due to the severe drought and hot conditions. No stripe rust was scored for the commercially grown cultivars. No significant differences in both test weight and yield between the sprayed and non-sprayed plots for all cultivars, including the susceptible check. The results indicated that under severe drought and hot conditions, stripe rust could not develop to the levels reducing test weight and yield and that fungicide application could not make differences in test weight and yield on spring wheat.