Transcript Unit 10: Soybean Diseases

Unit 10: Soybean
Diseases
Unit 10: Soybean Diseases
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Bacterial Blight
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Occurs on leaves of the SB
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Small angular spots
Appear yellow at first
Later turn brown to black
Diseased leaves eventually die and fall
Spots can spread from leaves to stem and
pods
Can spread rapidly in a field
Bacteria are seed-borne
Unit 10: Soybean Diseases
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Bacteria can overwinter on dead leaves
Crop rotation and tillage can reduce possible
infestation
Some varieties may have partial resistance
Bacterial Pustule
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Foliar disease
Light-green spots in early stages that develop
into red-brown spots on the leaves
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Portions of the infected spots on leaves often drop
out
Unit 10: Soybean Diseases
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Overwintering
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Treatment
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Stays on diseased seed
Stays on diseased plant materials
Bury diseased plant material w/ tillage
Crop rotation
Resistant varieties are available
Warm-weather disease developing after
bacterial blight
Unit 10: Soybean Diseases
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Sclerotinia Stem Rot
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Mostly confined to the Corn Belt states
Mold disease that has migrated from infection
of edible beans
Requires cool, wet summer
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May not be a problem every year
Spores infect the blossoms, most visible during
pod development
Leaves wilt and turn gray before dying
No effective control
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Phytophthora Root & Stem Rot
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One of the most serious SB diseases in the
U.S.
Occurs when exposed to cool, wet conditions,
on poorly drained soils
Can kill seed and seedlings during germination
and emergence
Seedlings wilt and appear water-soaked
Disease attaching older plants
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Dark brown discoloration from soil line upward
Unit 10: Soybean Diseases
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Secondary infections may occur
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Below ground
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White fungal growth on top of rotting areas
Tap root dark brown
Root system rots
Control methods
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Resistant varieties are best
Fungicide seed treatment can help control
Unit 10: Soybean Diseases
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Brown Stem Rot
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Caused by soil-inhabiting fungus
Decays the interior of the stem
Attacks the plant early in the season
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Symptoms are slow developing
Often not observed until infection is in advanced
stages
Center of diseased plants are reddish brown
Crop rotation is the best control
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Rotate out for 2 years
Unit 10: Soybean Diseases
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Pod & Stem Blight
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Can occur wherever SB are grown
Stem & pod can be heavily dotted black, spore
filled sacs
Effects
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May girdle stem
Kill plant
Prevent seed development
Fungus can penetrate seed and destroy subsequent
germination
Unit 10: Soybean Diseases
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Overwintering
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Control methods
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Survives in infected seeds
Stays on diseased plant material
Crop rotation
Plant disease-free seed
Downy Mildew
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Fungal disease
Seed-borne
First leaves of infected seeds unfold w/ mildew
on them
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Control
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No resistant varieties
Must use crop rotation, tillage, and disease-free seed
Purple Stain
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Symptoms
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Pink to dark purple stain on seed
Reduces seed value in the market
Seedlings from diseased seed may die
Control
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Use treated seed
High quality seed
Unit 10: Soybean Diseases
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Asian Soybean Rust
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Severe foliar damage
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Destroys photosynthetic tissue
Early defoliation
Early maturation
Yield losses can be 10-80%
6 hours of wet conditions and temps 59-82º
ideal for germination
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Dry conditions will restrict it
Unit 10: Soybean Diseases
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Spores penetrate cells directly instead of wait
for another opening in the leaf
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9-10d from initial infection to next stage of spore
production
Common hosts include kudzu, vetch, yellow
sweet clover
Spreads w/ wind patterns