Asian Soybean Rust University of Illinois State Soybean Rust Taskforce Suzanne Bissonnette, IPM Educator
Predicted Spore Deposition by a Hypothetical Hurricane Weather-Based Assessment of Soybean Rust Threat to North America, Final Report to APHIS, 15 July 2004, Scott Isard, et al.
Hurricane “Ivan” the TerribleModeled Spore Deposition Map December 3, 2004 As presented in: US Soybean Rust Detection and Aerobiological Modeling, November, 2004, http://www.aphis.usda.gov/lpa/issues/sbr/sbr.html
Soybean Production Distribution and Rust detections December 6, 2004
Action Plan for Soybean Rust • Illinois state rust taskforce plan • http://www.agr.state.il.us/regulation/soybeanrustprogram.pdf • Collaboration of state, federal, university, private, grower and applicator organizations • Initial detection, diagnosis, and confirmation • Field DDDI plant clinic national mycologist notificationmanagement
Soybean Rust Identification Two species differentiated based on microscopic morphological differences in teliospore characteristics Phakopsora meibomiae (mild) Phakopsora pachyrhizi (Asian Soybean Rust, severe) Ono, Buriticá and Hennen - 1992 Cross-section uredia Cross section telia
Spread of Soybean Rust Natural –windborne urediniospores produced in large quantities under moderate temperatures and high humidity. Life cycle ~7-10 days, infection to spore production. Artificial – movement of infected live plants, leaf material, pods, and stems. Soybean Rust is not seed borne. Soybean Rust will not over winter on dead plants.
Hosts of Soybean Rust (>90) Legumes (Papilionoideae) Cultivated Crops: • Soybean Glycine max • Lima & butter bean Phaseolus lunatus • Green & kidney bean Phaseolus vulgaris • Cowpea Vigna unguiculata • Pigeon pea Cajanus cajan • Yam bean, jicama Pachyrhizus erosus Ornamental plants: • Hyacinth bean, lupine, • royal poinciana Wild hosts: • Kudzu, sweet clover Kudzu infected with soybean rust
Kudzu population Distribution and Rust detections December 6, 2004
Asian Soybean Rust on Kudzuover wintering host, early inoculum source?
Yield Loss From Soybean Rust Is a Result Of: • Premature defoliation • Increase in number of unfilled pods/plant • Decrease in # of seeds/plant • Decrease in seed weight • Decrease in germinability of seed • Yield losses begin at approx. 3% severity
Management of Soybean Rust, Illinois Research program • Short-term solutions • Fungicide evaluations • Long-term solutions • Host resistance • Specific resistance • Partial resistance • Yield stability (tolerance) • Introduction of resistance from other sources • Combination of fungicides and resistance • Glen L. Hartman1, Monte Miles1, and Reid Frederick2, 1USDA-Agricultural Research Service,Department of Crop Sciences, National Soybean Research Center University of Illinois, Urbana, IL,2FDWSR, Fort Detrick, Frederick, MD
Breeding Programs Historical Screening of Germplasm • Initial studies • 1961 ≈ 2,800 accessions screened in Taiwan (U.S collection) • 1970 ≈ 4,000 accessions screened in India (U.S. Collection) • 1975 ≈ 1,675 accessions (MG V-X) screened in Taiwan (AVRDC) • From these studies, sources of resistance were found and the inheritance of resistance was characterized
Evaluation of U.S. And Exotic Germplasm for Resistance to Soybean Rust & Disease Management Strategies • Determine the resistance/susceptibility of soybean varieties currently grown in the U.S. to soybean rust • Identify resistance in the germplasm • Evaluate 16,000 accessions in the USDA National Soybean Collection (Fort Detrick) • Evaluate reported sources of resistance (Fort Detrick & international locations) • Evaluate yield stability (tolerance) Frederick, Bonde, Yang & Hartman, UBS Supported)
Fort Detrick Maryland Containment Research Facilities (secured greenhouse etc.) • Only location in continental US where Soybean rust research has been allowed to date
Identified Partial Resistance(epidemic is slowed due to fewer pustules or spores)
Rust Phenotypespustule types for evaluation in greenhouse or field • Tan pustule • A fully susceptible reaction • Reddish brown pustule (RB) • Indicates some type of resistance Tan Reddish Brown (RB)
Preliminary Summary of Field Evaluations • Not one soybean accession was found to be resistant at all locations • Known single genes had less disease severity in some sites, but also TAN and RB lesions at other sites
B. US Commercial Variety Entries • 940 cultivars were screened in a single plant screen • 212 were screened an a second single plant screen, with two inoculation dates, 14 and 28 days after planting • None were resistant C Stone
Disease Scouting for Soybean Rust** • Typical disease patterns • Random spots in field with diffuse borders ** • Field edges • Whole field** • Patterned • Headlands, historical, mechanical • Low / high spots ** Expect these patterns for rust
Assessment of Disease • Incidence: • The number of plants (or units) affected by disease with in a population • ie 47 of 100 plants diseased= 47% incidence • ie 34 of 100 leaflets diseased= 34% incidence • Severity: • The measure of actual damage done by disease • Some keys measure severity of the whole plant • Some keys measure severity on infected leaves
Assessment of Rust Severity • Researchers generally assess rust disease as disease severity of key leaves. • Rust pustules only occupy a maximum of 37% of the area on a leaf. This is equivalent to 100% infection of that leaf.
Rust Severity Assessment Key A= actual amount of tissue occupied by pustules (Cobb scale) B= equivalent damage to leaf (Modified Cobb) * If A=18.5% area occupied by pustules, this is equivalent to B=50% damage to the leaf *
Disease Scouting for Soybean Rust Incidence • U of I currently recommends determining incidence rather than severity for scouting protocol. • Examine 20 plants in 5 random locations in a field. • Note: one plant with any amount of rust in 100 plants = 1% incidence
Soybean Rust Scouting Field Pattern • Scout in a zig-zag pattern in the field making observations of 20 plants in 5 locations
Illinois Scouting –“Look Low As You Go” • When scouting examine the lower quarter of soybean plants • Examine the undersides of leaves for pustules. • If you suspect rust • collect 20 leaflets exhibiting symptoms. • Place flat, dry leaflets between paper towels. • Double bag suspect leaflets in zip lock bags. • Clearly label sample.
IL Extension Distance Diagnostics(DDDI Available in all Units in Illinois) Sample Process • digital images submitted for you by Unit • Diagnosis email reply to Unit • Samples may then require submission to U of I Plant Clinic.
IL Extension Distance Diagnostics(DDDI Available in all Units in Illinois) • No fee for DDDI samples. • Plant Clinic fee ($12.50) paid by ISPOB if sample is pre-screened with DDDI • Expect to pay overnight shipping prior to detection in state.
Symptoms & Signs of Soybean Rust • Look for pustules and chlorosis on undersides of lower leaves before flowering. • Severity increases with time and rainfall – lesions can develop on all leaves followed by defoliation Observe chlorosis Look at underside of leaves Observe pustules with hand lens
Other Soybean Diseases that Can Be Confused with Soybean Rust • Septoria Brown Spot J. Pataky U of I
Other Soybean Diseases that Can Be Confused with Soybean Rust • Bacterial Pustule • Bacterial Blight
Other Soybean Diseases that Can Be Confused with Soybean Rust • Downy Mildew
Protectant +/- absorbed +/- translocated Prevent infection or sporulation Use before infection Strobilurins, chlorothalonils Curative Absorbed Translocate Kill fungal tissue Use after infection Triazoles What You Need to Know About Rust Fungicide Types
Fungicide ** Trade Name Family Action Chlorothalonil Bravo Weather Stik, Echo 720 & 90DF Chloronitriles (Benzonitriles) Protectant Azoxystrobin Quadris Strobilurin Protectant Pyraclostrobin Headline Strobilurin Protectant Myclobutanil Laredo EC & EW Triazole Curative Propiconizole Tilt, Propimax, Bumper Triazole Curative Tebuconazole Folicur Triazole Curative **Section 3 compounds in green, others Section 18 (1/19/05) Fungicides Registered for Treatment of Soybean Rust or With EPA Section 18 NOTE: only a total of 2 applications of Sec 18 products are allowed in 1 season
Fungicide** Trade Name Family Action Pyraclostrobin + Boscalid Pristine, pending? Strobilurin + Carboximide Protectant Tetraconazole Domark, pending Triazole Curative Propiconizole + Trifloxystrobin Stratego, approved Triazole + Strobilurin Curative + Protectant Azoxystrobin + Propiconizole Quilt pending (6.2-12 oz) 0.5% COC Triazole + Strobilurin Curative + Protectant Additional Fungicides That Have or May Get EPA Section 18’s NOTE: only a total of 2 applications of Sec 18 products are allowed in 1 season
Fungicides Strategy for Soybean Rust Management in S. America, S. Africa • General Brazil (J. Yorinori): • Application at first detection • Second spray 15-20 days later for protective fungicides • 20-25 days later for protective/curative fungicides. • Timing of the first spray depends on when the first infection is detected, weather conditions, and mode of action of the fungicide • General Zimbabwe (C. Levy, M. Miles, G. Hartman): • Apply first spray soon after flowering • Apply second application 14-20 days later • Third application only in a severe epidemic
Fungicide Spray Recommendations(lessons from other countries) • Protectant (strobilurins,chloronitriles): Apply prior to infection. Strobilurins loose effectiveness after 3-5% severity. Strobilurins no more than once /season • Curative (triazoles): Apply when rust is present. After 10% severity triazoles may not provide full yield protection.
What Should We Do in Illinois? • Scenario A: • Disease Expected • Rust expected, not yet present • Apply Protectant Fungicide (Benzonitriles, Strobilurins) • Disease still expected now need 2nd spray • Apply Curative (Triazole)
What Should We Do in Illinois? Scenario B • Disease expected & develops after 1st application • Disease expected not yet present • Strobilurin, Benzonitriles • Disease expected or now present need 2nd spray • Triazole • Disease still present need 3rd application • Benzonitriles (PHI), Triazole