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Asian Soybean Asian Soybean Rust: Scouting Rust: Scouting & Sampling in & Sampling in
IllinoisIllinoisUniversity of IllinoisState Soybean Rust Taskforce
Suzanne Bissonnette, IPM Educator
Brand New EditionsBe ready with effective scouting
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
• 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.
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
Rust Severity Assessment Key
*
Disease Scouting for Soybean Rust Incidence
• U of I recommends determining incidence rather than severity for scouting protocol.– Note: one plant with any amount of
rust in 100 plants = 1% incidence
Illinois Scouting –“Look Low As You Go”
• When scouting examine the lower quarter of soybean plants– Examine 20 plants in 5 random
locations in a field.– Examine the undersides of leaves
for pustules.
Soybean Rust Scouting Field Pattern
• Scout in a zig-zag pattern in the field making observations of 20 plants in 5 locations
Foliar Symptoms Soybean Rust
not distinguishing must look closer
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
Look at underside of leaves
Observe pustules with hand lens
Observe chlorosis
Soybean Rust PustulesUnderside leaves*, Stems, Petioles,
Cotyledons
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
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 poincianaWild hosts: • Kudzu, sweet clover Kudzu infected with soybean rust
Kudzu population
Distribution and
Rust detections
December 6, 2004
Illinois Scouting –“Look Low As You Go”
• 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.
Sample Action Plan & Submission Flow Chart
Sam ple is sent to U of I P lant Clinic
Yes
Continue to subm it suspicious sam ples
No
Does Sam ple require further testing?
Sam ple taken to DDDI Extension Unit
Sam ple is collected according to protocol
Sample Submission Flow Chart, cont.
G row er receives instructionson further action
IF Sam ple positive forP . pachyrhizi
Action taken by Federal andState Agencies
Sam ple sent toUSDA/APHIS Beltsville MD
Yes No
Does sam ple require further testing?
Sam ple is sent Overnight Delivery Until Confirm ation in ILUniversity of Illinois P lant Clinic
1401 W . St. M ary's RoadUrbana IL 61802
Prepare Yourself for Soybean Rust Before It
Arrives• Equip sprayers with proper nozzles• Pre-plan fungicide spray program
– Who? How much acreage/day?
• Plan to scout “Low as you go” weekly
• Take representative sample• Get it properly identified
Acknowledgements:
Presentation by S. Bissonnette, D.
Bowman, D. Malvick, M. Montgomery
Acknowledge slides & jpg’s from G. Hartman, M. Miles, USDA-ARS, R. Frederick, M. Palm and University of Illinois Extension