Institute of Ag Professionals Proceedings of the 2004 Crop Pest Management Shortcourse www.extension.umn.edu/agprofessionals Do not reproduce or redistribute without the written consent of author(s).
Foliar diseases of soybean that look like soybean rust. Jim Kurle Department of Plant Pathology University of Minnesota - St. Paul
Soybean Rust in Minnesota Unlikely that Rust will Overwinter in MN Rust will Survive in Gulf Coastal Areas Texas, Louisiana, Florida Spores will Follow the Puccinia Pathway Risk Analysis Indicates Likelihood of Weather Conditions Favorable for Epidemic 6 to 15 out of 30 Years.
Soybean Rust Management Currently No Resistant Varieties Available Management Timely Application of Fungicides Protectant Fungicides Applied Before Infection Eradicant & Curative Fungicides Provide Control after Infection (Must be applied very early in disease cycle.) Identification of soybean rust will be critical.
Soybean Rust Identification Identification of soybean rust requires training and experience. A number of other foliar diseases are easily confused with soybean rust. This presentation is intended to help you identify those diseases that can be confused with soybean rust. By eliminating instances where lookalike diseases occur diagnostic resources can be focused on symptoms that might be those of soybean rust.
Soybean Rust Disease Development is favored by: Prolonged leaf wetness, High humidity (>75-80%). Temperatures between 59-86 F, Optimum 77 F Presence of Spores
Soybean Rust Obligate parasite. Infection begins on lower, older, leaves. Initially forms chlorotic spots. Leaf may become chlorotic. Spots become lesions. Lesions develop into pustules and increase in size; change from gray to tan or reddish brown.
Soybean Rust Pustules may also occur on stems, petioles, and pods. Pustules break open and reveal tan to reddish brown spores.
Soybean Rust When scouting for soybean rust, focus on: Early planted fields with early maturing varieties. Low lying or protected fields with prolonged dew periods. Fields with early canopy closure.
Soybean Rust For soybean rust detection on the plant: Examine lower leaves of the plant. Use a 10 to 20X hand lens to detect pustules on underside of leaves. Use a 10 to 20X hand lens to detect spores released from pustules.
Soybean Rust Lesions http://www.aphis.usda.gov/lpa/issues/sbr/soybean_rust_22.pdf
Soybean Rust Symptom Development Chlorotic Spots Visible on upper and lower sides of leaf Lesion Development Tan lesions form in chlorotic spots, predominantly on underside of leaf. Pustule Formation Lesions enlarge and form a blisterlike pustule at center, usually underside of leaf. Pustule Development Pustules increase in size. Spore Release Spores released from pore formed at tip of pustule. Free spores present on underside and sometimes topside of leaf.
Early Soybean Rust Chlorosis, or yellowing may be visible On upper leaf surface. USDA-ARS FDWSRU USDA-ARS FDWSRU USDA-ARS FDWSRU
Soybean Rust http://www.aphis.usda.gov/ppq/ep/soybean_rust/detection.html Levy Earliest stages found on undersides of older leaves Photo from "Soybean Rust," a Certified Crop Adviser Institute educational module. http://www.crops.org/soybean_rust/
Soybean Rust http://www.aphis.usda.gov/ppq/ep/soybean_rust/detection.html T Schanz Chlorosis, yellowing visible through leaf NO HALO! Lesions on upper surface OSU OSU http://www.oardc.ohio-state.edu/ohiofieldcropdisease/soybeans/soyrust_files/ soy%20rust%20id%20card%20nov%202004.pdf
Soybean Rust Closeup Lesions on lower leaf surface Photos Courtesy USDA-ARS FDWSRU
Soybean Rust Closeup 5x 40x Pustules on lower leaf surface 15x Pustules releasing uredospores Photos Courtesy USDA-ARS FDWSRU
Foliar diseases of soybean that might be mistaken for soybean rust. Bacterial Blight Bacterial Pustule Frogeye Leafspot Cercospora Blight Downy Mildew Septoria Leaf Spot
Bacterial Blight Bacterial Blight Symptoms: Affects mid-to-upper leaves. Angular lesions, reddish brown to black centers. Initial angular water soaked lesions with yellow halo. Difference from Soybean Rust: Water soaking; angular lesions; Lesions on leaf underside are not raised.
Bacterial Blight Angular red-brown lesions at center of halo Angular red-brown lesions http://www.psu.missouri.edu/ soydoc/files/disease/bacblight1.pdf Yellow halo http://www.aphis.usda.gov/ppq/ep/soybean_rust/detection1.html
Bacterial Pustule Bacterial Pustule Symptoms: Affects mid-to-upper leaves. Lesions small spots to large irregular shapes without water soaking. Lesions associate with main veins. Pustules form in lesion centers on leaf underside and topside. (10X) Difference from Soybean Rust: Pustules not always with each lesion. Pustules do not have spores in openings. Openings are cracks instead of circular pores.
Bacterial Pustule Lesions associate with main veins Alemu Mengistu USDA-ARS Pustules in lesion centers Glen Hartman, NSRL http://www.aphis.usda.gov/ppq/ep/soybean_rust/detection1.html
Frogeye Leaf Spot Symptoms of Frogeye Leaf Spot: Affects lower leaves first. Lesions start as dark, water-soaked spots; can have light centers; Lesions become circular to angular brown spots with dark red-brown margins. Difference from Soybean Rust: Discrete lesions larger than rust with defined lesion margins. No pustules evident on underside.
Frogeye Leaf Spot Lesions start as dark, water-soaked spots Discrete large lesion, Brown margin, light center Alemu Mengistu USDA-ARS
Cercospora Blight Symptoms of Cercospora Blight: Blight affects upper leaves exposed to sun after seed set. Blight starts as light purple areas on upper leaf surface which expands to cover surface; Leaves leathery and dark reddish purple on upper surface only. Difference from Soybean Rust: Overall leaf area is discolored on upper surface only. Bronzed tissue not in discrete lesions.
Cercospora Blight Leaves leathery, dark reddish purple X.B. Yang X.B. Yang http://www.ent.iastate.edu/imagegal/ plantpath/soybean/cercospora/1778.4cercleafspot.html
Downy Mildew Downy Mildew Symptoms: Affects upper leaves. Spots on surface enlarge into yellow lesions. Older lesions turn brown with yellow-green margins; size varies with age of leaf affected. Fuzzy fungal gray tufts on leaf underside (20x). Difference from Soybean Rust: Lesions larger than rust lesions. No raised pustules on underside. Fuzzy fungal growth on underside.
Downy Mildew Chlorotic spots become yellow lesions Fuzzy gray tufts on leaf underside http://www.psu.missouri.edu/ soydoc/files/disease/downy1.pdf http://www.ent.iastate.edu/imagegal/plantpath/soybean/ downymildew/1778.6downymild.html
Septoria Brown Spot Symptoms of Brown Spot Affects lower leaves first. Irregular-shaped dark brown lesions on both leaf surfaces; size small spots to large areas; Adjacent lesions can form irregular shaped blotches. Infected leaves quickly yellow and drop. Difference from Soybean Rust: No raised areas (on leaf) underside; Angular lesions. Lack of uredia is key symptom. However: Early symptoms can look like rust. Has same canopy distribution as rust.
Septoria Brown Spot Dark brown lesions on both leaf surfaces Gail Ruhl Gail Ruhl http://www.ppdl.purdue.edu/ppdl/weeklypics/weekly_picture6-11-01-1.html
Septoria Brown Spot & Bacterial Blight Compared with Soybean Rust Irregular, dark brown lesions, Halo, redbrown Irregular lesions at brown lesionscenter Chlorotic spot, tan lesion at center Septoria Brown Spot Bacterial Blight USDA-ARS FDWSRU http://www.ipm.iastate.edu/ipm/icm/1997/7-21-1997/icompare.html
Soybean Rust When scouting for soybean rust, focus on: Early planted fields with early maturing varieties. Low lying or protected fields with prolonged dew periods. Fields with early canopy closure.
Soybean Rust For soybean rust detection on the plant: Examine lower leaves of the plant. Look for early chlorotic spotting. Use a 10 to 20X hand lens to detect pustules on underside of leaves. Use a 10 to 20X hand lens to detect spores released from pustules.
Soybean Rust Identification Currently First Detectors are being trained to help in disease identification. Their role will be to assist and train growers in disease identification. Training: A Cooperative Effort of The University of Minnesota, Minnesota Extension Service, Minnesota Department of Agriculture, Minnesota Soybean Research and Promotion Council
Plant Disease Clinic University of Minnesota 495 Borlaug Hall 1991 Upper Buford Circle University of Minnesota St. Paul, MN 55108-6030 (612) 625-1275 Web URL: http://www.extension.umn.edu/distribution/cropsystems/dc3170.html
For More Information http://www.aphis.usda.gov/ppq/ep/soybean_rust/ http://www.planthealth.info/rust/rustfaq.htm Fact sheet: http://www.oardc.ohiostate.edu/ohiofieldcropdisease/soybeans/soyrust_files/soy%20rust% 20ID%20card%20nov%202004.pdf http://www.aphis.usda.gov/ppq/ep/soybean_rust/uremelpp502.pdf http://www.apsnet.org/online/feature/rust/