Disease forecast 2011: Viruses and stripe rust Dr. Mary Burrows Montana State University Bozeman, MT

Virus diseases in MT Occur sporadically Difficult to predict Host PathogenEnvironment Vector

Wheat streak mosaic virus Infects both winter and spring wheat Earlier infection = greater yield loss Grassy weeds, volunteer wheat, corn, etc. can harbor both WSMV and the mite vector

Disease cycle of WSMV

2010: Distribution of WSMV

Weed Host: Volunteer Wheat

Average yield loss (%) due to mechanically inoculated WSMV in winter wheat, , Bozeman *Hail damage

Average yield loss (%) due to mechanically inoculated WSMV in spring wheat, , Bozeman

Insecticides/Acaracides: NONE! ChemicalTrade NameStatus CarbofuranFuradan 4FDelisted by EPA as of Jan 2010 ClorpyrifosLorsbanNot labelled for WCM, no efficacy (WCM protected in leaves/whorl) ImidaclopridGauchoNot labelled for WCM, no efficacy, may increase WCM (Harvey J. Agric. Urban Ent. 20:7-10) ThiamethoxamCruiserNot labelled, no efficacy SpiromesifenOberonMay have efficacy, not labelled for wheat (Sec. 3 is pending)

C. Tharp, Southern Ag Research Center, Huntley, MT, 2010

Barley yellow dwarf virus: The Host Infects barley, wheat, oats, rye, corn, triticale, rice Resistance has been developed, but predicting the virus and aphid populations from year to year can be difficult (no resistance in Montana varieties)

Barley yellow dwarf virus (BYDV) Family Luteoviridae –Genera Luteovirus, Polerovirus, Enamovirus First classified by primary aphid vector MAV: Macrosiphum (Sitobion) avenae PAV: Rhopalosiphum padi and S. avenae RMV: Rhopalosiphum maidis SGV: Schizaphis graminum RPV: Rhopalosiphum padi (& S. graminum) (Cereal yellow dwarf virus – RPV)

Russian wheat aphidCorn leaf aphid English grain aphid Greenbug Note leaf damage caused by feeding toxins (RWA and greenbug) RWA is NOT a vector of BYD

2010: Distribution of BYD majority of samples tested negative, even in the counties with confirmed BYD

Control of WSMV vs. BYDV Insecticides are effective against BYD, but generally not economical; no acaracides are available for WCM/WSMV control Plant resistance can be effective, but viruses and mites evolve rapidly; none available in MT Prevent movement from volunteer plants by getting rid of volunteers before planting (green bridge)

The rusts Jim Berg, MSU Stripe Stem Leaf

Leaf rust, stem rust: ‘Puccinia pathway’ Stripe rust: gen’l WA or Canada

What qualifies as excitement for a plant pathologist:

Aecia on barberry Uredinia on Kentucky bluegrass Pycnidia on barberry Aecia on barberryUredinia on wheat Jin, Szabo and Carson, Plant Dis., 2010

Fall 2010: Distribution of stripe rust Does occur on spring wheat, but generally too late to be significant

Fall infection by stripe rust, 2010 WSMV and stripe rust: lucky guy!

Stripe Rust: variety resistance is very effective at reducing yield losses Yellowstone Promontory Johnston & Grey, 2006 Susceptible varietyResistant variety

Big Sky (Susceptible) Influence of fungicide application on two stripe-rust infected WW varieties (Quilt, 14oz, Bozeman 2007; P < 0.001, LSD = 6.3) Yellowstone (Resistant) a b b b c cc c

Influence of fungicide application on susceptible SW variety, McNeal Quilt, Bozeman 2007, P = 0.50

Stripe rust variety evaluation: Winter wheat Bozeman, 2006 VarietyYield (Bu/a) % Stripe rust (June 28) Yellowstone997 Promontory939 Jerry8910 NuFrontier8510 Rampart8018 Pryor8042 Jagalene7912 CDC Falcon7855 Genou7136 Ledger7041 Neeley7072 NuSky6682 NuWest6583 Correlation = p < Grey, 2006 Note: Jagalene is susceptible to the new strain, had high disease severity at Huntley, 2010

Xiangming Chen, WSU, 2010 Stripe rust would have caused 54% yield loss in WA without fungicide application in 2010 if all varieties were as susceptible as PS279 If all resistant cultivars were grown, 1% yield loss with no fungicide application Resistant check Susceptible check

Acknowledgements Dai Ito, Zach Miller, Matt Moffet, Linnea Skoglund GPDN: Jim Stack & all state reps and diagnosticians MSU County Extension Agents

Ug99 First reported in Uganda in Pretorius et al Plant Dis 84:203 Virulent on Sr31 Sr31 is located on 1BL.1RS translocation Also carries Lr26, Yr9 Increased adaptation and higher yield. As a result, widely spread in wheat worldwide Helped to reduce stem rust population worldwide Virulence to Yr9, originated in the eastern Africa in mid 80s, caused worldwide epidemics

TTKS In 2002 and 2004, CIMMYT nursery planted in Njoro, Kenya were severely infected by stem rust. In 2005, we identified Kenyan isolates from 2004 were race TTKS. --Wanyera, Kinyua, Jin, Singh 2006 Plant Dis 90:113

Broad virulence of TTKS to North American spring wheat  US spring wheat CVs of the Northern Great Plains, known to have broad-based resistance to stem rust, were mostly susceptible (84%).  500 CIMMYT CVs released since 1950’s, 84% were susceptible. Conclusion: Ug99 possesses a unique virulence combination that renders many resistance genes ineffective. Jin & Singh, 2006, Plant Dis:90:

% of resistance to TypeEntryTTKSKTTKSTTTTSK (Ug99)Sr24vSr36v Hard red spring8921%12%21% Hard red winter41629%15%28% Soft red winter37727%25%11% Western wheat603%3%3% Total94226%18%19% Ramification of Sr24/Sr36 virulence to US Wheat based on testing of 2007 elite breeding germplasm

Current status of Ug99 New races constantly evolving Ug99 stalled in Iran due to long drought If moves to Pakistan/India will affect 15% of world’s wheat crop that feeds 1 billion of the world’s poorest people Strain of stem rust in India that overcomes Sr25 ‘Likely’ Ug99 has already spread beyond Iran - Rick Ward, co-coordinator of the Durable Rust Resistance in Wheat project, based at Cornell university; Rust Resistance in Wheat project

Projected potential pathways for Ug99 based on the migration of Yr9 virulence Singh et al CAB Review 1, 54

Ug99 migration Singh et al Advances in Agronomy v ? ?

The good news Phil and Luther are both working on it already! Li Huang, PSPP, has identified spring wheat mutants from a population derived by Mike Giroux with resistance to leaf, stem, and stripe rust – including all Ug99 derivatives Fungicide trials with great results Communication and education ramping up!

Triazoles Triazole + Strobilurin

Fungicide modes of action: Triazoles FRAC group 3 DMI (demethylation) inhibitors; biosynthesis of sterols in fungal cell membrane; spore penetration and mycelial growth Provides days of protection Medium risk of resistance development Greater mobility in plant than strobilurin fungicides Most widely used class of fungicide in the world Control a wide array of fungal diseases Protective and curative effects (if applied early in disease development)

Fungicide movement in the plant From: Tenuta, A., D. Hershman, M. Draper and A. Dorrence Using foliar fungicides to manage soybean rust.. Land-Grant Universities Cooperating NCERA-208 and OMAF. Available online at state.edu/SoyRust/

Fungicide modes of action: Strobilurins FRAC group 11 QoI (quinone outside) inhibitors (respiration); spore germination, penetration, and mycelial growth Provides days of protection High risk of resistance development because it has a very specific mode of action (they block electron transfer at the site of quinol oxidation (the Qo site) in the cytochrome bc 1 complex, thus preventing ATP formation) Originally isolated from wood-rotting fungi Strobilurus tenacellus ‘Reduced-risk’ pesticide (pose less risk to human health than other chemical options at the time of registration by EPA) Control a wide array of fungal diseases Excellent preventative fungicides, but limited curative effects “Plant health benefit” independent of disease control?

Figure 1. Mobility of trifloxystrobin, an example of a QoI fungicide. /Strobilurin/top.htm

Stem rust fungicide trial RateActive IngredientCompany 1.Control 2.Proline 480 SC5.3 ozProthioconazoleBayer 3. Prosaro 421 SC7.5 ozTebuconazole + ProthioconazoleBayer 4. Quilt14 ozAzoxystrobin + PropiconazoleSyngenta 5. A15590C14 ozAzoxystrobin + PropiconazoleSyngenta 6. Alto 100SL4 ozCyproconazoleSyngenta 7. Caramba13.5 oz MetconazoleBASF 8. Twinline9 oz Pyraclostrobin +Metconazole BASF 9. Headline 2.09EC7.5 ozPyraclostrobinBASF 10. Gem 500 SC2.4 ozTrifloxystrobinBayer

Yield, stem rust fungicide trial 2009, Bozeman a bcd cd bc a cd d bc b

Control (no fungicide), 14 daa

Strobilurin fungicides, 14 daa Headline Gem 500 SC

Strobiliurin + Trizole, 14 daa Quilt Quilt Xcel

Strobiliurin + Trizole, 14 daa Prosaro Twinline

Trizole fungicides, 14 daa Alto Proline Caramba

Compare sprayed and unsprayed plots