Field Crop Diseases Craig Grau Plant Pathology UWMadison Soybean Corn Wheat Alfalfa

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Field Crop DiseasesCraig Grau Plant Pathology
UW-Madison SoybeanCorn WheatAlfalfa
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Soybean Cyst Nematode in Wisconsin

• State-wide distribution
• Early detection is critical for control
• Improved resistant varieties available

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• Soybean cyst nematode  (SCN), Heterodera
  glycines, have been confirmed in 44 Wisconsin
  counties as of October 2007. This includes a new
  county record for Fond du Lac County in 2007.
• SCN is the leading economic pest of soybeans in
  Wisconsin.

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Signals Indicating SCN Problems

• Yield potential of field declines
• Patches of low yield plants
• Slow canopy closure
• Wilted plants in low areas
• Late season flushes of weeds
• No white mold

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SCN SCN and crop canopy
Resistant variety
Susceptible variety
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SCNWeeds in patches breaking through the crop
canopy
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Detection of SCN on Soybean Roots

• Important to dig plants
• Carefully remove soil to
• expose SCN on roots

SCN on roots
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Nonuniform distribution of SCN Likely SCN Hotspot
s Shaded In White SCN favored by high soil pH
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• Sample and
• Test Soil for SCN
• Any time
• Estimate population density of eggs
• Coordinate with fall soil samples for fertility

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Diagnosis of Soybean Cyst Nematode

• Detection of SCN on soybean roots
• Soil samples
• Detection of SCN
• Population density
• Eggs/100 cc soil
• Loam soils - gt1000 eggs/100 cc soil
• Sandy soils - gt 250 eggs/100 cc soil

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SCN Resistance

• Several sources of resistance used by soybean
  industry
• PI 88788 (95 of varieties)
• Peking
• Hartwig
• Current resistance suppression of SCN
  reproduction
• Races of SCN
• Races affect performance of specific SCN
  resistant varieties

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Stem Canker
Sclerotinia Stem Rot
Phytophthora Stem Rot
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Sclerotinia Stem Rot/White MoldSclerotinia
sclerotiorum

• Sclerotia long-lived in soil
• Pathogen not present in all soybean fields
• Greater activity in high yield potential fields
• Introduction into fields
• Movement of contaminated soil
• Planting of infected and contaminated seed
• Local dispersal of ascospores

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Symptoms and Signs
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Pathogen x Soybean x Environment
Inoculum Canopy Management soil moisture and
light Tillage no-till lowers risk Crop rotation
small grains lower risk Biological control
Host Partially resistant cultivar Pesticides
fungicide herbicides
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Factors that Influence Sclerotinia Stem Rot
Development
As canopy closure is increased, the potential for
Sclerotinia development is increased. A dense
canopy decreases radiation penetration and
increases humidity within the canopy resulting in
a more favorable environmental conditions.
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Management of Sclerotinia Stem Rot

• Host resistance
• No complete resistance
• Partial resistance
• Cultivars vary in response
• Crop management
• Plant population row width
• Tillage no-till lowers risk
• Weed cultivation as late as possible
• Crop rotation with small grains
• Chemical
• Fungicides
• Herbicides
• Biocontrol
• Coniothyrium minitans formulated as Contans

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Stem Canker DiagnosedCharacterized by brown stem
lesions
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Stem CankerLeaf Retention Variety Differences
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Stem Canker
Phytophthora races Resistance genes Rps1a not
effective Rps1c not always Rps1k some
failure Rps6 not common use Field
resistance/tolerance Fungicide seed treatments
Phytophthora Stem Rot
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Maturity differences or disease?If disease,
which one?
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Brown Stem Rot Risk Factors Short crop
rotations Varieties differ Soil pH lt6.5
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Brown Stem Rot vs Sudden Death Syndrome
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Symptoms of SDS and BSR
SDS
BSR
Foliar
Internal stem
Root
asymptomatic
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Pattern of symptom development for SDS and BSR
BSR
SDS
Leaf drop with petiole retention for SDS
Growth stage when symptoms observed
R3 to R4
R5 to R6
Leaves may remain attached for BSR
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SDS and SCN frequently found together in the same
fields
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Disease Diagnosis at Harvest
Purple Seed Stain Cercospora leaf blight
Mottled seed coats Virus SMV BPMV
Sclerotia White mold
Phomopsis seed rot Premature plant death
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Corn Diseases
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Lodged Corn Stalk Rot
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Anthracnose disease cycle
Bergstrom and Nicholson, 1999
Root infection
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Corn AnthracnoseStalk phase most yield limiting
August 22, 2006
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Corn Anthracnose

• Root infection into stalk
• Premature plant death
• Direct infection of stalk
• Stalk rot and lodging

Factors Hybrids differ in susceptibility Survives
in stalk debris Warm weather Nitrogen less at
higher rates
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Major Corn Leaf Diseasesin Wisconsin
Eyespot
Northern Corn Leaf Blight
Gray Leaf Spot
Gray Leaf Spot
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Corn Leaf Health and YieldFungicides?

Extensive blight
Minimal blight
Yield Difference 27 bu/a
Gary Munkvold Iowa State University
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Tassel and upper plant appearance can be used to
evaluate corn health
Dropped tassels associated with European corn
borer. Dropped tassel symptom continues with Bt
hybrids Portion of dropped tassels Attributed to
disease
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Corn Hybrids and Plant Health
Hybrid B
Premature dry down
Hybrid A
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Plant Parasitic Nematodes
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Nematodes and Corn Health

• Root lesion nematode Pratylenchus
• Most common and all soil types
• Needle nematode Longidorus
• Sandy soils only
• Occurrence
• Corn on corn
• Non-nematicidal corn root worm insecticide
• Approach to corn rootworm
• Insecticides Counter and Furadan are nematicides
• Pyrethroids no nematicidal effects
• GMO hybrids no known contribution to nematode
  control

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Chronic symptoms Yield decline N K deficiency
Acute Symptoms Stunted plants in patches
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Nematodes destroy feeder roots
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Nematodes

• Microscopic and not observed on roots
• Soil sample at border between normal and
  symptomatic plants
• Sample in July August
• Testing labs

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Nematodes and Corn Health

• Control
• Crop rotation
• Insecticide/Nematicide products
• Need to treat GMO rootworm hybrids with
  insecticide/nematicide products??
• No consistent information on corn hybrid reaction

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Wheat Diseases
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Virus Pathogens of Small GrainsBarley yellow
dwarf virus
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BYDV Yellow/purple flagleaf Confusion with
N deficiency prior to flagleaf
Variety differences Planting date early
results in greater BYDV potential Timing of
killing frost modifies planting date effect
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Corn is a host to BYDV inoculum reservoir for
BYDV
Aphids acquire virus from corn Migrate to winter
wheat
Photo by Gary Munkvold
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Wheat Leaf Diseases
Powdery mildew
Stripe rust
Septoria leaf blotch
Leaf rust
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Leaf Rust of WheatPuccinia recondita

• Most common rust of wheat
• Dependent on southern inoculum
• Varieties differ in reaction
• Fungicides to protect flag leaf
• Delay planting of winter wheat to reduce
  infection in fall

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Leaf rust Stripe rust
Fungicides Varieties will differ in reaction
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Head Scab of Wheat

• Cause Fusarium graminearum
• Yield loss and mycotoxins
• Sources of inoculum
• Host residue
• Soil
• Favorable environment
• Infection at flowering
• Warm temperatures
• High moisture

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Wheat into corn residueIncreases risk of
Fusarium head scab
Same fungus causes ear rot and stalk rot of corn
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Symptoms of Take-all
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AlfalfaAphanomyces Race 2

• Becoming more widespread
• Possible problem for fields with establishment
  problems using Aphanomyces Race 1 resistant
  varieties.
• Soil test to confirm presence of Aphanomyces Race
  2

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Field plant to alfalfa variety resistant to Race
1 of Aphanomyces Aphanomyces Race 2 is
predominent form of pathogen in field
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Typical symptoms of Aphanomyces root rot Stunted
seedlings yellow and purple leaves
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Aphanomyces Race TestSoil SampleSend ½ gallon
of soil toPlant Disease Diagnostics
ClinicDepartment of Plant PathologyUniversity
of Wisconsin-Madison1630 Linden DriveMadison,
WI  53706-1598
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Aphanomyces Race 2
Additional Detections Wood Co. Marathon
Co. Columbia Co.
Survey by UW Plant Disease Diagnostic Lab
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Aphanomyces Race 2 Resistant Alfalfa Varieties

• Variety Resistance Marketer
• GH 757 HR Golden Harvest
• GH 707 HR Golden Harvest
• Platinum HR Crows Hybrids
• A4440 HR Producers Choice
• Bobwhite HR Blue River Hybrids
• Withstand HR Allied Seed
• 53V52 HR Pioneer Hybrid Intl
• Ameristand 403 R Americas Alfalfa
• 4 Traffic R Kaltenberg Seed
• 54V46 R Pioneer Hybrid Intl.
• A 30-06 R PGI Alfalfa
• WL 348 AP R FS Growmark Olds Seed
  Solutions
• Trump II R Ottilie
  Seeds
• Phabulous II R Trelay Seeds
• Phabulous III R Trelay Seeds
• Integrity R Producers Choice
• 6325 R Garst/Agripro
• 4R429 R Mycogen Seed

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Soybean Leaf Disease Complex
Downy Mildew
Brown Spot
Bacterial Blight Fungicides have no effect
DM fungus on lower leaves
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Powdery Mildew of Soybean80 soybean varieties
resistantFungicides Triazoles, Topsin-M
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Frogeye LeafspotSouthern Wisconsin
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Cercospora Leaf Blight
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Fungicides and Soybean Leaf Health
Arlington ARS
LaCrosse Co.
54.9 bu/a
57.5 bu/a
55.5 bu/a
52.7 bu/a
Fungicide
No fungicide
Fungicide
Marshfield ARS
50.1 bu/a
56.2 bu/a
No fungicide
Fungicide
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Wisconsin Soybean Insect-Virus Complex
Soybean mosaic virus
Bean leaf beetle Marlin Rice ISU
Soybean Aphid
Bean pod mottle virus
Alfalfa mosaic virus
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Soybean VirusesSoybean mosaic virus, Alfalfa
mosaic virus and Bean pod mottle virus
Aphids
Mottled Seed SMV BPMV
Green Stem SMV BPMV
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Soybean RustSymptoms and Signs