2019 First Stripe Rust Forecast and 2018 Fungicide and Variety Yield Loss Tests

January 8, 2019

Xianming Chen

A. Field survey in November 2018

On November 16, 2018, our crew was checking winter wheat fields in Whitman, Lincoln, Adams, Grant, and Douglas counties in eastern Washington and found two leaves with stripe rust (Figure 1) in only one field in Grant County near the border with Lincoln County. Wheat plants in that field were at Feekes 4. The observations indicated a relatively normal level of stripe rust infection before the winter in eastern Washington.

B. The 2019 first forecast of stripe rust for the eastern Pacific Northwest

Based on the weather conditions in November and December 2018, stripe rust in the 2019 wheat growing season will likely be in the upper normal epidemic level range (20-40% yield loss). According to the forecast models, highly susceptible winter wheat varieties would have yield loss ranging from 27 to 48% with an average of 38%. Currently grown varieties would have yield losses from 0 to 19% depending upon the level of resistance or susceptibility. If this forecast is close to the real disease level, fields grown with moderate susceptible or susceptible winter wheat varieties (stripe rust ratings 5 to 9) would need the early fungicide application at the time of herbicide application. Based on the past experience, the early prediction made in January is often close to the real situation, but not better than the prediction in March based on the entire winter weather conditions. Therefore, we will make another prediction in early March.

C. Yield losses caused by stripe rust and increases by fungicide application on wheat varieties tested in 2018

The data of stripe rust and yield differences in non-sprayed and fungicide-sprayed plots in our experimental fields near Pullman in 2018 are shown in Table 1 for winter wheat and Table 2 for spring wheat.

Of the 24 winter wheat varieties tested, including 23 commercially grown varieties and a susceptible check (‘PS 279’), 10 varieties (PS 279, Xerpha, Eltan, SY 107, Keldin, Puma, Whetstone, ARS-Crescent, UI Sparrow, and SY Ovation) had significant differences in stripe rust severity, presented as relative area under the disease progress curve (AUDPC), between their non-sprayed and sprayed treatments. The percentage of severity reduction by fungicide application in these varieties ranged from 4.4% (SY Ovation) to 93.2% (PS 279) (Table 1). Four varieties (PS 279, Xerpha, Eltan, and SY 107) had significant differences in grain test weight with increases from 3.6 lb/bu (SY 107) to 10.9 lb/bu (PS 279) by fungicide spay. Significant yield differences, ranging from 19.1 bu/A (Rosalyn) to 69.6% (PS 279) were observed for 10 varieties (PS 279, Xerpha, Eltan, SY 107, Keldin, ARS-Crescent, Whetstone, Westbred 528, LCS Jet, and Rosalyn). Stripe rust caused 70.5% yield loss on the susceptible check (PS 279) and from 0 to 40.7% yield losses (average 10.1%) on commercially grown varieties. Fungicide application increased grain yield by 0 to 40.2% (average 12.4%) on commercially grown varieties. Under such a severe level of stripe rust epidemic, 6 commercially grown varieties (Xerpha, Eltan, SY 107, Keldin, ARS-Crescent, and Whetstone) received fungicide application rating 2, which needs fungicide application. Six varieties (Westbred 528, LCS Jet, ORCF 102, Rosalyn, Otto, and UI Sparrow) were rated 1 for fungicide application, which may or may not need fungicide application. The remaining 11 varieties (SY Ovation, Bobtail, Puma, Jasper, Legion, Madsen, Skiles, Bruehl, Cara, Farnum, and Norwest 553) received fungicide application rating 0, which does not need fungicide application.

Similarly, of the 24 spring wheat varieties tested including 23 commercially grown varieties and one susceptible check (‘AvS’), 19 varieties had significant differences and 5 varieties (Seahawk, Dayn, WB9518, JD, and WB6121) had no significant differences in stripe rust severity (presented as relative AUDPC) (Table 2). Eight varieties (AvS, Babe, WB6341, WB-1035CL+, SY605CL, Kelse, Whit, and Louise) had significant differences in grain test weight. Grain yield losses of sprayed and non-sprayed plots were significantly different for nine commercially grown varieties (Babe, WB6341, WB-1035CL+, SY605CL, Kelse, Whit, Louise, Solano, and Tekoa) in addition to the susceptible check (AvS). Stripe rust caused 66% yield loss on the susceptible check and from 0 to 47.5% (average 13.8%) yield losses on commercially grown varieties. Fungicide application increased grain yields by 0 to 90.6% (average 20.1%) on commercially grown varieties. Nine varieties (AvS, Babe, WB6341, WB-1035CL+, SY605CL, Kelse, Whit, Louise, and Solano) received fungicide application ratings 2 to 5, which need fungicide application. Six varieties (Tekoa, Alum, Glee, Buck Pronto, and Melba) received rating 1, which may or may not need fungicide application. The remaining ten varieties (SY Steelhead, SY Selway, Seahawk, Dayn, Express, Diva, Chet, WB9518, JD, and WB6121) received rating 0, which does not need fungicide application under the rust pressure in 2018.

The data can be used to select stripe rust resistant varieties to plant and to determine if fungicide application is needed for a variety based on its relative yield loss and potential epidemic level. Based on the current forecasted epidemic level (38% yield loss on susceptible varieties) for 2019 (see above), fungicide application would be needed for the varieties with a fungicide application rating 2 or higher, or stripe rust ratings 5-9 as mentioned above. Varieties with fungicide application ratings 0 and 1, or stripe rust ratings 1 to 4 in the Seed Buyer’s Guide, would not need fungicide application in 2019.

D. Fungicide tests in 2018

In 2018, a total of 31 fungicide treatments, plus a non-treated check, were evaluated for stripe rust control efficacy on both winter wheat and spring wheat in fields near Pullman, Washington under natural infection of stripe rust.

In the winter wheat field, stripe rust from natural infection started developing in the plots in early May when plants were at the early jointing stage (Feekes 5) and reached 100% severity in middle Jun at the milk stage, in the non-treated check plots (Table 3). All fungicide treatments, except one (treatment 16), significantly reduced relative AUDPC, an overall measurement of rust

severity, compared to the non-treated check. However, all treatment with only the early (Feekes 5) application did not completely stop rust development as severity reached 100%, the same as the non-treated check, at the milk stage. The treatments with only the late (Feekes 8) application produced the better control results than those of only early application. The best reduction of stripe rust was provided by treatments 5 (Quilt Xcel 7.0 at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 8), 13 (Topguard EQ 7.0 fl oz/A at Feekes 5 followed by Topguard 7.0 fl oz/A at Feekes 8), and 25 (Prosaro 6.5 fl oz/A at Feekes 5). Twenty two treatments significantly increased test weight compared to the non-treated check, but treatments 25 (Prosaro 6.5 fl oz/A at Feekes 8) and 27 (A15457 4.11 fl oz/A + A12705 6.02 fl oz + A7402 6.84 fl oz/A at Feekes 8) produced the highest test weight. Seven treatments, which all had only the early application, did not significantly increase yield compared to the non-treated check, while the remaining 24 treatments produced significantly higher grain yield. Treatments 5 (Quilt Xcel 7.0 at Feekes 5 followed by Trivapro 13.7 fl oz/A at Feekes 8) produced the highest yield.

The spring wheat field was planted on May 4, later than the normal planting date for the Palouse region due to the wet field condition. Stripe rust started developing in the field in early June. About 1-5% rust severity were recorded in the plots on June 8 just before the early application (Feekes 6). The second application was done on June 27 (Feekes 10) when stripe rust reached 20-25% severity in the non-treated plots. Rust severity reached 100% severity in the non-treated check plots by the flowering stage (Feekes 10.5). All 31 fungicide treatments significantly reduced stripe rust AUDPC values, but treatments 5 (Quilt Xcel 7.0 fl oz/A at Feekes 6 followed by Trivapro 13.7 fl oz/A at Feekes 10), 31 (Tilt 4.0 fl oz/A at Feekes 6 followed by Tilt 4.0 fl oz/A at Feekes 10), and 32 (Tilt 4.0 fl oz/A at Feekes 6 followed by Quilt Xcel 14.0 fl oz/A at Feekes 10) provided the best control (Table 4). Twenty two treatments significantly increased grain test weight compared to the non-treated check with treatment 25 (Prosaro 6.5 fl oz/A at Feekes 10) producing the highest test weight. All treatments, except treatment 16, significantly increased grain yield, and the increases ranged from 9.1 bushel per acre (26%) by treatment 2 (Alto 3.0 fl oz/A at Feekes 6) to 60 bushes (172%) by treatment 32 (Tilt 4.0 fl oz/A at Feekes 6 followed by Quilt Xcel 14.0 fl oz/A at Feekes 10).

Stripe rust on winter wheat.
Figure 1. Stripe rust found in a winter wheat field in Grand County on November 16, 2018.
Table 1. Differences in stripe rust severity (as rAUDPC), test weight, and yield in non-sprayed and fungicide sprayed plots of winter wheat varieties tested under natural infection of the stripe rust pathogen near Pullman, WA in 2018.

Stripe rust severity difference in test weight and yield in non-sprayed plots of winter wheat varieties.

Table 2. Differences in stripe rust severity (as rAUDPC), test weight, and yield in non-sprayed and fungicide sprayed plots of spring wheat varieties tested under natural infection of the stripe rust pathogen near Pullman, WA in 2018.

Stripe rust difference in severity, test weight, and yield in non-sprayed spring wheat varieties.

Table 3. Stripe rust severities and relative area under the disease progress curve (AUDPC), test weight, and yield in susceptible winter wheat (‘PS 279’) field plots not sprayed (No fungicide) or sprayed with various fungicide treatments under natural infection of the stripe rust pathogen near Pullman, WA in 2018.

Stripe rust severities in susceptible winter wheat plots not sprayed or sprayed with fungicide treatments.

Table 4. Stripe rust severities and relative area under the disease progress curve (AUDPC), test weight, and yield in susceptible spring wheat (‘AvS’) field plots not sprayed (No fungicide) or sprayed with various fungicide treatments under natural infection of the stripe rust pathogen near Pullman, WA in 2018.

Stripe rust severities in test weight and yield for spring wheat in plots not sprayed with fungicide.

Washington State University