Control of stripe rust of winter wheat with foliar fungicides, 2005

Authors: Chen, Xianming; Wood, David

Submitted to: Scientific and Technical Review
Publication Type: Research Technical Update
Publication Acceptance Date: 3/1/2006
Publication Date: 4/20/2006
Citation: Chen, X., Wood, D.A. 2006. Control of stripe rust of winter wheat with foliar fungicides, 2005. F&N Tests 61:CF023.

Interpretive Summary: The study was conducted in a field under natural infection of stripe rust near Pullman, WA. Urea (46-0-0) was applied at the time of cultivation. Susceptible ‘PS 279’ wheat was seeded in rows spaced 14 in. apart on 13 Oct 04. Harmony Extra plus Buctril with Agridex was applied on 2 May 05 when wheat plants were at tillering stage. Urea (46-0-0) was broadcast on 14 May. Fungicides were applied in water on 21 May at late jointing stage when stripe rust severity was at 20-40% on leaves. Sprays were applied when wind was between 2.5 and 0.5 mph and temperature was about 51-61°F. In the treatment with two sprays of Quilt plus COC, the first spray was applied on 21 May at late jointing and a second spray was applied on 6 Jun at boot stage. Stripe rust severity (percentage of diseased foliage) was assessed in each plot on 21 May just before fungicide application; 31 May or 10 days after fungicide application; 6 Jun or 16 days after fungicide application at boot stage; 15 Jun or 25 days after fungicide application at early heading stage; and 23 Jun or 33 days after fungicide application at late flowering stage. Plots were harvested on 15 Aug when kernels were naturally dry, and test weight of kernels was measured for each plot. Stripe rust severity in non-treated control plots was 32.5, 80, 95, 100, and 100% on 21 May, 31 May, 6 Jun, 15 Jun, and 23 Jun, respectively. All fungicide treatments effectively reduced stripe rust severity 10 days after application. Except Quadris, all treatments were effective in maintaining disease control up to 16 days after fungicide application. By 25 days after fungicide application, treatments with Absolute, Sparta, Quilt, Tilt and Folicur showed better control of stripe rust, than Stratego. Rust severity increased to 40, 50, and 62.5% in the plots treated with Flutriafol, Headline, and Quadris, respectively, indicating that these treatments had become less effective before 15 Jun or 25 days after application. By 33 days after application, stripe rust severity in plots treated with Tilt, Headline, Flutriafol, Stratego, and Quadris were not significantly different from the non-treated control plot. The treatments with Absolute and two-applications of Quilt remained effective, while plots treated with Sparta, Folicur, and one application of Quilt showed a significant increase of rust severity. Only the treatments with Absolute, Sparta, or two applications of Quilt significantly increased test weight. All fungicide treatments significantly increased yield by 145 to 286% of the yield of the non-treated control. Stripe rust damage was much higher and the yield response to fungicide treatments was much greater in 2005 compared to previous field trials (2000-2004), because of the long duration of the epidemic season in 2005.

Technical Abstract: The study was conducted in a field with Palouse 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 ‘PS 279’ wheat was seeded in rows spaced 14 in. apart at 60 lb/A with an experimental drill planter on 13 Oct 04. Harmony Extra 0.33 oz plus Buctril 0.75 pt/A with Agridex at 1% of spray volume was applied on 2 May 05 when wheat plants were at tillering stage. Urea (46-0-0) was broadcast at 60 lb/A on 14 May. Fungicides were applied in 16 gal water/A on 21 May at late jointing stage when stripe rust severity was at 20-40% on leaves. Sprays were applied when wind was between 2.5 and 0.5 mph and temperature was about 51-61°F. 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. In the treatment with two sprays of Quilt plus COC, the first spray was applied on 21 May at late jointing and a second spray was applied on 6 Jun at boot stage. A randomized block design was used with four replications for each treatment. Plots were individually measured at the time of harvest, and plot area ranged from 52.5 to 88.4 sq ft. Stripe rust severity (percentage of diseased foliage) was assessed in each plot on 21 May just before fungicide application; 31 May or 10 days after fungicide application; 6 Jun or 16 days after fungicide application at boot stage; 15 Jun or 25 days after fungicide application at early heading stage; and 23 Jun or 33 days after fungicide application at late flowering stage. Plots were harvested on 15 Aug 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 treatment using the five 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. Stripe rust severity in non-treated control plots was 32.5, 80, 95, 100, and 100% on 21 May, 31 May, 6 Jun, 15 Jun, and 23 Jun, respectively. All fungicide treatments effectively reduced stripe rust severity 10 days after application. Except Quadris, all treatments were effective in maintaining disease control up to 16 days after fungicide application. By 25 days after fungicide application, treatments with Absolute, Sparta, Quilt, Tilt and Folicur showed better control of stripe rust, than Stratego. Rust severity increased to 40, 50, and 62.5% in the plots treated with Flutriafol, Headline, and Quadris, respectively, indicating that these treatments had become less effective before 15 Jun or 25 days after application. By 33 days after application, stripe rust severity in plots treated with Tilt, Headline, Flutriafol, Stratego, and Quadris were not significantly different from the non-treated control plot. The treatments with Absolute and two-applications of Quilt remained effective, while plots treated with Sparta, Folicur, and one application of Quilt showed a significant increase of rust severity. The relative AUDPC of treatments were significantly lower than the non-treated control, but varied significantly because of differences in the duration of efficacy. Only the treatments with Absolute, Sparta, or two applications of Quilt significantly increased test weight. All fungicide treatments significantly increased yield by 145 to 286% of the yield of the non-treated control. Stripe rust damage was much higher and the yield response to fungicide treatments was much greater in 2005 compared to previous field trials (2000-2004), because of the long duration of the epidemic season in 2005.