Control of stripe rust of spring wheat with foliar fungicides, 2011

Authors: Chen, Xianming; Evans, Conrad; Garner, John

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2012
Publication Date: 3/30/2012
Citation: Chen, X., Evans, C.K., Garner, J.P. 2012. Control of stripe rust of spring wheat with foliar fungicides, 2011. Plant Disease Management Reports. 6:031.

Interpretive Summary: A total of 15 fungicide treatments were tested for their efficacy in control of stripe rust on winter wheat during the 2011 crop season. The experimental field near Pullman, WA was planted with a susceptible spring wheat cultivar, Lemhi, on May 4, 2011. A randomized complete block design experiment with four replications was used including a non-treated check treatment. Fungicides were applied on two different dates and stages depending upon the treatments. Disease severity was assessed from each plot five times during the disease season under the natural infection of stripe rust. Area under the disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. Relative AUDPC was calculated as percentage of the non-treated control. Grain yield and test weight were measured. Rust severity, relative AUDPC, test weight, and yield data were subjected to analysis of variance and means were compared to determine the difference among the treatments. Stripe rust caused more than 40% yield loss in the non-treated control plots. All fungicide treatments significantly reduced rust severity compared to the non-treated control at flowering stage. The treatments with an early fungicide application at jointing stage provided better disease control and produced more grain than the treatments with only a late application at boot stage. All treatments significantly increased test weight compared to the non-treated control. Yield increases ranged from 18.6% to 66.1%.

Technical Abstract: The study was conducted in a field with Palouse silt loam under natural infection of stripe rust near Pullman, WA. Fertilizer (Osmocota 14-14-14) 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 (99% germination rate) with a drill planter on 4 May 11. Huskie 15 fl oz plus R-11 30 ml/A was applied on 26 Jun when wheat plants were at early jointing stage. Before the first fungicide application, the field was divided into individual plots of 4.3 ft (4 rows) in width and 15.1-18.0 ft in length by eliminating plants between plots with a rototiller. Fungicides were applied in 16 gal water/A on different dates and stages depending upon the treatments. The first fungicide application timing at early jointing stage was done on 26 Jun when stripe rust was 20-40% severity and the second at boot stage on 6 Jul when stripe rust in the unsprayed plots reached 50-70% severity. A 601C backpack sprayer was used with a CO2 pressurized spray boom at 18 psi having three operating nozzles spaced 19 in apart. A randomized block design was used with four replications. Disease severity (percentage of diseased foliage on whole plot) was assessed from each plot on 28 Jun, 6 Jul, 20 Jul, 2 Aug, and 15 Aug or 2, 10, 24, 37, and 50 days after the first fungicide application timing, respectively. Plots were harvested on 15 Sep when kernels were naturally dry, and test weight of kernels was measured. Area under disease progress curve (AUDPC) was calculated for each plot using the four 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. Because the considerable level of stripe rust had developed by the fungicide application dates, none of the treatments provided complete protection of the crop from the disease. However, all fungicide treatments significantly reduced rust severity compared to the non-treated control at flowering stage. Relative AUDPC values of all treatments were significantly less than the non-treated control, and were significantly different among some of the treatments. Priaxor (4 fl oz/A and 5 fl oz/A), Twinline (both 7 fl oz/A and 9 fl oz/A), Headline (3 fl oz/A) plus Tilt (4 fl oz/A), Tilt (4 fl oz/A), Quilt (14 fl oz/A), and Stratego YLD (4 fl oz/A) applied at boot stage had similar relative AUDPC values, which were significantly lower than that of the non-treated control, but significantly higher than treatments with Priaxor (2 fl oz/A), Headline (3 fl oz/A), and Tilt (2 fl oz/A) applied at jointing stage and Priaxor (2 fl oz/A) at jointing stage followed by Twinline (7 fl oz/A) at boot stage or Headline (3 fl oz/A) at jointing stage followed by Priaxor (4 fl oz/A) at boot stage. All treatments with an early application at jointing stage had the lowest relative AUDPC values. All treatments significantly increased test weight compared to the non-treated control. The treatments with an early application at jointing stage all increased grain yield significantly compared to the non-treated control. All treatments of the late application at boot stage increased grain yield; however only the increases by treatments of Twinline (both 7 fl oz/A and 9 fl oz/A) and Tilt (4 fl oz/A) were statistically significant. Yield increases ranged from 18.6% by the treatment of Priaxor (5 fl oz/A) at boot stage to 66.1% by the treatment of Priaxor (2 fl oz/A) applied at jointing stage and the treatment of Priaxor (2 fl oz/A) applied at jointing stage followed by Twinline (7 fl oz/A) at boot stage. The non-treated control had 40% yield loss compared to the treatment producing the highest grain yield.