Control of stripe rust of spring wheat with foliar fungicides, 2008

Authors: Chen, Xianming; Wood, David

Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: 5/1/2009
Publication Date: 6/30/2009
Citation: Chen, X., Wood, D.A. 2009. Control of stripe rust of spring wheat with foliar fungicides, 2008. Plant Disease Management Reports 3:CF039.

Interpretive Summary: Wheat stripe rust can cause severe damage on grain yield and quality. This study was conducted in 2008 to determine efficacy of a couple of new fungicide formulations on control of stripe rust of spring wheat. A total of 11 treatments of 5 fungicides, including new formulations Topguard and BAS 556, were tested in a field expriment of randomized split-block design with 4 replications under natural infection of stripe rust. All fungicide treatments significantly reduced stripe rust severity 7 days after the second application in the field. Differences in stripe rust severity between the fungicide treatments and non-treated control remained significant thereafter. Relative AUDPC values of all fungicide treatments were significantly lower than the non-treated control (100%), but varied significantly (0.4 – 14.2%) among the treatments. All treatments significantly increased grain test weight and the increases ranged from 0.99 to 1.52 lb/bu. All treatments significantly increased grain yield by 14.9 to 24.2% compared to the non-treated check. The treatments of two applications of Topguard at 10 or 14 fl oz/A produced the highest yield. The results should be useful for registering these two fungicides for control of wheat stripe rust.

Technical Abstract: The study was conducted in a field with Palous silt loam under natural infection of stripe rust near Pullman, WA. Urea (46-0-0) was applied at 60 lb/A at the time of cultivation. Susceptible ‘Lemhi’ spring wheat was seeded in rows spaced 14 in. apart at 60 lb/A with an experimental drill planter on 22 Apr 08. Harmony Extra 0.33 oz plus Buctril 0.75 pt/A with Agridex crop oil concentrate (COC) at 1% of spray volume was applied on 30 May when wheat plants were at tillering stage. Fungicides were applied in 16 gal water/A on different dates and stages depending upon the treatments. The first applications of Topguard for the two-application treatments were done on 12 Jun at late jointing stage when there was no stripe rust in the plots. Sprays were applied when wind was 3.6 mph and temperature was about 58 oF. The one-time applications of Topguard, Headline, BAS 556, Quilt, and Stratego and second application of Topguard were done on 25 Jun when plants were at early boot stage and stripe rust just appeared in the plots. Sprays were applied when wind was 2.2 mph and temperature was about 74 oF. A 601C backpack sprayer from R & D Sprayers Inc. was used with a C3470 regulator and a 2.5 lb CO2 cylinder. The spray boom had four nozzles 19 in apart, but three were used because of the width of the plots. The spray pressure was 18 psi. A randomized block design was used with four replications for each treatment. Plots, ranging from 77.5 to 89.6 sq ft., were individually measured at the time of harvest and individual plots areas were used to calculate yields. Stripe rust severity (percentage of diseased foliage) was assessed in each plot on 25 Jun just before the second fungicide application and 2 Jul (early flowering), 7 Jul (late flowering), 15 Jul (milk), 23 Jul (soft dough), and 31 Jul (dough) or 7, 12, 20, 28, and 36 days after the second fungicide spray, respectively. Plots were harvested on 1 Sep when kernels were naturally dry, and test weight of kernels was measured for each plot. Area under disease progress curve (AUDPC) was calculated for each plot using the six sets of severity data. Relative AUDPC was calculated as percent of the non-treated control. Rust severity, relative AUDPC, test weight, and yield data were subjected to analysis of variance and means were separated by Fisher’s protected LSD test. Mean stripe rust severity in non-treated control plots was 1.0, 17.5, 52.5, 92.5, 100.0, and 100.0% on 25 Jun, 2 Jul, 7 Jul, 15 Jul, 23 Jul, and 31 Jul, respectively. All fungicide treatments significantly reduced stripe rust severity 7 days after the second application in the field. Differences in stripe rust severity between the fungicide treatments and non-treated control remained significant thereafter. Relative AUDPC values of all fungicide treatments were significantly lower than the non-treated control (100%), but varied significantly (0.4 – 14.2%) among the treatments. All treatments significantly increased grain test weight and the increases ranged from 0.99 to 1.52 lb/bu. All treatments significantly increased grain yield by 14.9 (Stratego at 10 fl oz/A) to 24.2% (two applications of Topguard at 14 fl oz/A).