Unit 10: Soybean Diseases

Unit 10: Soybean Diseases Bacterial Blight

Occurs on leaves of the SB 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

Bacteria can overwinter on dead leaves Crop rotation and tillage can reduce possible

infestation Some varieties may have partial resistance

Bacterial Pustule Foliar disease Light-green spots in early stages that develop

into red-brown spots on the leaves Portions of the infected spots on leaves often drop

out

Unit 10: Soybean Diseases

Overwintering Stays on diseased seed Stays on diseased plant materials

Treatment Bury diseased plant material w/ tillage Crop rotation

Resistant varieties are available Warm-weather disease developing after

bacterial blight

Unit 10: Soybean Diseases Sclerotinia Stem Rot

Mostly confined to the Corn Belt states Mold disease that has migrated from infection

of edible beans Requires cool, wet summer

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

Unit 10: Soybean Diseases Phytophthora Root & Stem Rot

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

Dark brown discoloration from soil line upward

Unit 10: Soybean Diseases

Secondary infections may occur White fungal growth on top of rotting areas

Below ground Tap root dark brown Root system rots

Control methods Resistant varieties are best Fungicide seed treatment can help control

Unit 10: Soybean Diseases Brown Stem Rot

Caused by soil-inhabiting fungus Decays the interior of the stem Attacks the plant early in the season

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

Rotate out for 2 years

Unit 10: Soybean Diseases Pod & Stem Blight

Can occur wherever SB are grown Stem & pod can be heavily dotted black, spore

filled sacs Effects

May girdle stem Kill plant Prevent seed development Fungus can penetrate seed and destroy subsequent

germination

Unit 10: Soybean Diseases

Overwintering Survives in infected seeds Stays on diseased plant material

Control methods Crop rotation Plant disease-free seed

Downy Mildew Fungal disease Seed-borne First leaves of infected seeds unfold w/ mildew

on them

Unit 10: Soybean Diseases

Control No resistant varieties Must use crop rotation, tillage, and disease-free seed

Purple Stain Symptoms

Pink to dark purple stain on seed Reduces seed value in the market Seedlings from diseased seed may die Control

Use treated seed High quality seed

Unit 10: Soybean Diseases Asian Soybean Rust

Severe foliar damage 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 Dry conditions will restrict it

Unit 10: Soybean Diseases

Spores penetrate cells directly instead of wait for another opening in the leaf

9-10d from initial infection to next stage of spore production

Common hosts include kudzu, vetch, yellow sweet clover

Spreads w/ wind patterns