Soybean Disease Diagnostic Series

Fusarium solani, F. oxysporum, F. tricinctum and other Fusarium species (fungi)

Photo Credit:

B. Nelson, NDSU

FIGURE 1 – Dark brown/black discoloration of roots

Photo Credit:

Giesler, Univ. of Nebraska

FIGURE 2 – Root rot and dieback of tap root

Photo Credit:

J. Bienapfl, Univ. of Minnesota

FIGURE 3 – Seedling damping-off

Photo Credit:

D. Mueller, Iowa State Univ.

FIGURE 4 – Plant chlorosis

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Brown to black discoloration and rot of roots, especially the taproot
• Plant stunting and yellowing of leaves may occur if root rot is severe
• Seedling damping-off

FACTORS FAVORING DEVELOPMENT

• Soil compaction
• Presence of soybean cyst nematode (SCN)
• Plant stress
• Drought

IMPORTANT FACTS

• Disease can infect and kill seedlings and damage older plants
• Fusarium survives for long periods in soil
• Dry edible beans, corn and pulse crops are hosts
• Fusarium is dispersed with soil (on equipment, in water, by wind, etc.)
• Management: improve soil drainage, reduce compaction, fungicide seed treatments
• Commonly confused with other roots rots, SCN and iron deficiency chlorosis

Phytophthora sojae (oomycete)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Close-up of lower stem lesion

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Lower stem lesion and wilting

Photo Credit:

A. Dorrance, Ohio State Univ.

FIGURE 3 – Severe infection in field

AUTHORS: Sam Markell, Dean Malvick and Berlin Nelson

SYMPTOMS

• Seeds may rot and/or seedlings may die before or after emergence (damping-off)
• Mid- to late-season symptoms include a chocolate brown stem lesion extending up from the soil line
• Leaf chlorosis, necrosis and plant wilting can develop
• Frequently occurs in patches of fields and low areas

FACTORS FAVORING DEVELOPMENT

• Excessive moisture, saturated soil and/or flooding, especially early in the season
• Poorly drained, heavy clay or compacted soils
• Short/no crop rotation

IMPORTANT FACTS

• Can cause significant yield loss
• The pathogen is specific to soybeans
• Management tools available include genetic resistance and seed treatments
• The pathogen has many pathotypes and many can overcome Rps genetic resistance
• Commonly confused with other root rot diseases

Pythium ultimum and other Pythium species (oomycete)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Seed rotting due to Pythium

Photo Credit:

M. Chilvers, Michigan State Univ.

FIGURE 2 – Damping-off of seedlings

Photo Credit:

A. Robertson, Iowa State Univ.

FIGURE 3 – Light brown infected roots

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Soft, slimy rot of seeds in ground
• Light brown rot of outer part of roots (cortex)
• Damping-off of seedlings

FACTORS FAVORING DEVELOPMENT

• Persistent wet soil after planting
• Soil compaction, heavy soil with high clay content
• Slow growth of seedlings and plant stress

IMPORTANT FACTS

• Pythium survives for years in soil
• Pathogen causes most damage to seeds and seedlings, but may damage roots of older plants
• Dry edible beans, corn and other crops can be hosts
• Pythium is dispersed with soil (on equipment, in water, by wind, etc.)
• Management: improve soil drainage, reduce compaction, some seed treatments
• Symptoms on seed and seedlings very similar to Phytophthora damage
• Commonly confused with other seedling diseases

Rhizoctonia solani (fungus)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Rusty-brown lesions on soybean stems

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Soybean seedlings with girdled stems

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 3 – Seedlings dying in a row

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Rusty-brown, dry, sunken lesions on lower parts of stems
• Dark brown lesions than girdle the stems near the soil
• Plants stunted, yellow, and wilting

FACTORS FAVORING DEVELOPMENT

• Warm and moist soil while plants are in early vegetative stages
• Delayed planting in spring due to rain
• High soil organic matter
• Plant stress due to physical or chemical/herbicide injury

IMPORTANT FACTS

• Dry edible beans, corn, sugar beet and pulse crops can be hosts
• Causes most damage to plants in early vegetative growth stages
• Rhizoctonia is dispersed with soil (on equipment, in water, by wind, etc.)
• Management: some seed treatments, crop rotation, tillage, early planting
• Soybean varieties vary in susceptibility to Rhizoctonia
• Commonly confused with other roots rots

Pythium (oomycete), Phytophthora (oomycete), Rhizoctonia (fungus), Fusarium (fungus)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Seedling decomposing due to infection

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Pre-emergence death of seedling

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 3 – Post-emergence death of seedling

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Rotting of seed in the ground
• Pre-emergence death
• Post-emergence death and stunting
• Soft, tan roots with intact steel (Pythium and Phytophthora)
• Dark brown discoloration and rot of tap roots (Fusarium)
• Rusty-brown lesions on stem and roots (Rhizoctonia)

FACTORS FAVORING DEVELOPMENT

• Wet soil
• Delayed germination and growth
• Poor-quality seed
• Plant stress

IMPORTANT FACTS

• Pathogens are favored by different conditions for infection and disease development
• Multiple pathogens often infect seeds/seedlings
• Difficult to diagnose principle pathogen
• Symptoms can look similar for different pathogens, but management may differ
• Management options: soil drainage, tillage, varieties with resistance, seed treatments
• Seed treatment ingredients vary in efficacy for different pathogens
• Commonly confused with water damage

Heterodera glycines (plant parasitic nematode)

Photo Credit:

S. Markell, NDSU

FIGURE 1 – White SCN females (cysts) and a nodule on soybean roots

Photo Credit:

S. Markell, NDSU

FIGURE 2 – Mature brown cysts

Photo Credit:

S. Markell, NDSU

FIGURE 3 – Yellowed areas near field entrance caused by severe SCN

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Small (approximately 1/32 inch) lemon-shaped female worms (cysts) on roots
• Cysts’ color ranges from cream to dark brown
• Above-ground symptoms often are absent
• Soybeans can become stunted and yellow

FACTORS FAVORING DEVELOPMENT

• Short crop rotation with soybeans and/or dry edible beans
• High soil pH, light soil texture
• Dry growing seasons

IMPORTANT FACTS

• SCN is the most yield-limiting disease in the U.S.
• SCN can make other diseases (sudden death syndrome, brown stem rot) worse
• Soybeans, dry edible beans and several weeds are hosts
• SCN is dispersed with soil (on equipment, in water, by wind, etc.)
• Soil testing is the most reliable way to determine if you have SCN
• Management tools available include crop rotation, variety resistance and possibly seed treatments
• SCN is overcoming PI88788 genetic resistance
• Commonly confused with roots rots, iron deficiency chlorosis, other abiotic stress

Fusarium virguliforme (fungus)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Internal stem browning

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Early chlorotic blotches between veins

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Severe leaf symptoms

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 3 – Severe infection in a patch in a field

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 4 – Root rot and blue fungal growth on root

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Yellow and brown discoloration between leaf veins
• Tan stem under the epidermis near the soil line, while pith remains white
• Symptoms develop in plant seed fill stages (August)
• Leaflets can fall and petioles remain attached to plant
• Root rot and occasionally blue fungal growth on root

FACTORS FAVORING DEVELOPMENT

• Wet soil for two to four weeks after planting
• Field history of SDS
• Compacted soil, poor drainage
• Periodic heavy rain and moist soil through mid-Aug.
• High soybean cyst nematode populations

IMPORTANT FACTS

• Common in southern and central Minnesota, less common (but increasing) in northern Minnesota and North Dakota
• Pathogen can cause root rot of dry edible bean and some other legumes
• Pathogen dispersed with soil (on equipment, in water, by wind, etc.)
• Management options include varieties with resistance to SDS and seed treatments
• Commonly confused with brown stem rot

Colletotrichum truncatum or other Colletotrichum species (fungi)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Irregular-shaped blotches on stem

Photo Credit:

S. Markell, NDSU

FIGURE 2 – Abundant black fungal growths of irregular arrangement and size

Photo Credit:

S. Markell, NDSU

FIGURE 3 – Close-up appearance of fungal growths

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Symptoms usually not seen until plants reach maturity
• Dark brown patches may appear on stems, pods and petioles
• Small black fungal spots develop in irregular patterns on stems, pods and petiole
• Black, infected areas covered with tiny black spines (setae) that can be seen with a 10X hand lens

FACTORS FAVORING DEVELOPMENT

• Warm and wet/humid weather
• Planting infected seed
• Short/no crop rotation

IMPORTANT FACTS

• A common late-season disease that rarely causes significant yield loss
• Pathogen(s) have a wide host range and may infect other legume crops and weeds
• Pathogen can be seedborne
• Commonly confused with pod and stem blight, stem canker, charcoal rot

Cadophora gregata (fungus)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Light brown discoloration in pith and leaf

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Dark brown discoloration in pith of stem

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 3 – Brown and yellow discoloration between veins

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 4 – Symptoms on leaves of whole plant

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Brown pith in stem, especially in lower stem
• Brown and yellow discoloration between leaf veins may be present
• Symptoms commonly develop in mid-August

FACTORS FAVORING DEVELOPMENT

• Short/no crop rotation
• Wet and cool weather in July/August
• History of disease in a field
• Susceptible soybean varieties
• Presence of soybean cyst nematode

IMPORTANT FACTS

• Stems should be longitudinally split to identify BSR
• Commonly confused with sudden death syndrome
• Pathogen overwinters/survives in infected soybean stems
• BSR pathogen dispersed with soil (on equipment, in water, by wind, etc.)
• Soybean is only known definite host
• Two pathogen types: type A causes leaf and stem symptoms; type B primarily internal stem symptoms only
• Type B more common in our region
• Management options: crop rotation and varieties resistant to BSR

Macrophomina phaseolina (fungus)

Photo Credit:

B. Nelson, NDSU

FIGURE 1 – Large patch of soybean with charcoal rot

Photo Credit:

B. Nelson, NDSU

FIGURE 2 – Patch of wilting soybeans

Photo Credit:

B. Nelson, NDSU

FIGURE 3 – Infected (L and C) and healthy soybean (R)

Photo Credit:

S. Markell, NDSU

FIGURE 4 – External gray lesion peeling away, revealing profuse "charcoal" sclerotia

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Symptoms usually not apparent until flowering or later
• Taproot and lower stem may appear gray/silver
• Numerous black fungal specks (microsclerotia) under epidermis give a “charcoal” appearance
• Premature death with wilted leaves attached
• Frequently occurs in patches in fields

FACTORS FAVORING DEVELOPMENT

• Hot temperatures
• Drought stress

IMPORTANT FACTS

• Yield loss may occur in hot, dry growing seasons
• Disease typically most severe in drought-prone areas of fields
• Very wide host range, which includes corn, sunflower, other legume crops and weeds
• Commonly confused with anthracnose, Phytophthora stem rot, pod and stem blight, stem canker

Diaporthe longicolla (fungi) and D. sojae

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Linear rows of raised black dots

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Infected (L) and healthy (R) plants

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Small, raised black dots (pycnidia) arranged in distinct rows on stem, pods and petioles
• Tops of plants may discolor and die, leading to plant death
• Symptoms often not apparent until plants near maturity
• Wavy, black zone lines inside infected stems and roots may occur (see stem canker)
• Seed may be cracked, shriveled, moldy and have poor germination

FACTORS FAVORING DEVELOPMENT

• Warm and humid weather
• Short/no crop rotation
• Planting infected seed
• Delayed harvest due to wet weather

IMPORTANT FACTS

• Yield loss and reduction in seed quality may occur
• Host range includes dry edible bean and dry edible pea
• Pathogen survives in crop residue and seed
• Pathogen is widespread, even in apparently healthy plants
• Black dots arranged in rows are diagnostic (anthracnose and charcoal rot dots are random)
• Commonly confused with anthracnose, charcoal rot and stem canker

Diaporthe caulivora (northern stem canker) and D. aspalathi (southern stem canker) (fungi)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Reddish-brown stem canker lesion

Photo Credit:

S. Markell, NDSU

FIGURE 2 – Sunken canker on lower stem of mature plant

Photo Credit:

S. Markell, NDSU

FIGURE 3 – Zone lines beneath epidermis of sunken canker

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Reddish-brown lesions on the lower stem starting at branch points/nodes
• Lesions expand and may become sunken cankers
• Tiny black fungal structures may be produced on lesions
• Narrow black “zone lines” sometimes under epidermis, but importantly, zone lines also are associated with pod and stem blight

FACTORS FAVORING DEVELOPMENT

• Extended periods of wet weather (one to four days) with moderate temperatures (70 to 85 F)
• Short/no crop rotation in fields with history of disease
• Reduced tillage

IMPORTANT FACTS

• Yield loss can occur if disease is widespread in a field and kills plants before pod fill
• Management tools include crop rotation (wheat, corn, etc.), resistant varieties and foliar fungicides
• Commonly confused with anthracnose, charcoal rot, late-season Phytophthora root rot, and pod and stem blight

Sclerotinia sclerotiorum (fungus)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Lesions with white mold and sclerotia

Photo Credit:

M. Gilley, NDSU

FIGURE 2 – Severe white mold infection

Photo Credit:

S. Markell, NDSU

FIGURE 3 – Black sclerotia among shriveled seeds

Photo Credit:

S. Markell, NDSU

FIGURE 4 – Apothecia

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Stem lesions begin as water-soaked spots near nodes
• Lesions enlarge, fluffy white fungal growth develops on moist stems
• Infected stems become bleached white and may shred
• Hard black structures (sclerotia) form on and in infected tissue

FACTORS FAVORING DEVELOPMENT

• Wet soils prior to and during soybean flowering
• Frequent wetness (rain, fog, heavy dew) and cool temperatures during bloom
• Dense plant canopy, high fertility, high plant populations
• History of white mold in field

IMPORTANT FACTS

• Severe yield losses can occur when July and early August are cool and wet
• Many broadleaf crops and weeds are hosts
• Pathogen survives in soil for many years as sclerotia
• Sclerotia produce apothecia (about 1/4-inch mushrooms), which produce ascospores that initiate infection
• Management options: partially resistant varieties, increase plant spacing and fungicides
• Apothecia commonly confused with bird’s nest fungi

Pseudomonas savastanoi pv. glycinea (bacteria)

Photo Credit:

S. Markell, NDSU

FIGURE 1 – Brown angular lesions with bright yellow halos

Photo Credit:

S. Markell, NDSU

FIGURE 2 – Coalescing lesions and leaf tattering

Photo Credit:

S. Markell, NDSU

FIGURE 3 – Magnified lesions

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Typically observed first in upper canopy in July
• Small, water-soaked and angular leaf lesions
• Lesion centers turn brown and are surrounded by a bright yellow halo
• Lesions often coalesce and leaves will tatter
• Often widespread distribution in field

FACTORS FAVORING DEVELOPMENT

• Cool temperatures, frequent rains and thunderstorms
• Weather that damages plant tissue (hail, high winds, etc.)
• Short/no crop rotation
• Planting infected seed

IMPORTANT FACTS

• Widespread but rarely economically important
• Lesions may occur on stem, petiole and pod
• Pathogen survives and can be spread with seed and infested crop residue
• Fungicides are not effective
• Commonly confused with Septoria brown spot, bacterial pustule, downy mildew

Xanthomonas axonopodis pv. glycines (bacteria)

Photo Credit:

FIGURE 1 – Lesions with chlorotic halos on upper side of leaf

FIGURE 1 – Lesions with chlorotic halos on upper side of leaf

Photo Credit:

S. Markell, NDSU

FIGURE 2 – Lesions and pustules on underside of leaf

Photo Credit:

S. Markell, NDSU

FIGURE 3 – Pustules (approximately 5 to 10X)

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Lesions begin as small (1/16 to 1/4 inch) light green specks with yellow halos
• Lesion centers turn brown
• Raised pustules appear in lesions

FACTORS FAVORING DEVELOPMENT

• Wet and rainy weather
• Prolonged humid conditions
• Warm to hot temperatures

IMPORTANT FACTS

• Sporadic in Minnesota and North Dakota
• Unlikely to cause yield loss
• Can be mistaken for soybean rust, a disease that has not occurred in Minnesota or North Dakota
• Commonly confused with bacterial blight or Septoria brown spot

Photo Credit:

A. Dorrance, Ohio State Univ.

FIGURE 1 – Light green to yellow leaf mottling

Photo Credit:

A. Dorrance, Ohio State Univ.

FIGURE 2 – Wrinkling, puckering and light green mottling

Photo Credit:

Univ. of Illinois

FIGURE 3 – Leaf puckering and wrinkling

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Green to yellow mottling of young leaves
• Leaves may become puckered and wrinkled
• Symptoms may not be visible during high temperatures or after pod set
• Seed may become mottled with dark stains

FACTORS FAVORING DEVELOPMENT

• High populations of bean leaf beetle (or other beetles) early in the season
• Cool weather

IMPORTANT FACTS

• Not thought to be common in Minnesota and North Dakota
• Virus can be transmitted by bean leaf beetle or other leaf feeding beetles
• Infection primarily occurs early in the season
• Host range includes dry edible bean, clovers and other legumes
• Management options: delay planting, seed applied insecticides
• Commonly confused with other viruses and possibly herbicide injury

Cercospora kikuchii (fungus)

Photo Credit:

A.K. Chanda, Univ. of Minnesota

FIGURE 1 – Purple discoloration of leaf

Photo Credit:

A.K. Chanda, Univ. of Minnesota

FIGURE 2 – Bronze discoloration and death of leaf tissue

Photo Credit:

Univ. of Illinois

FIGURE 3 – Purple seed stain

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Purple to bronze discoloration of upper leaf surfaces
• Red-brown spots on both leaf surfaces
• Large necrotic areas can develop on leaves, followed by leaf drop
• Seed coats can develop purple discoloration

FACTORS FAVORING DEVELOPMENT

• High humidity and warm temperatures
• Lack of crop rotation

IMPORTANT FACTS

• Disease is more common and severe in southern U.S.
• Pathogen overwinters on infested soybean debris and seed
• Plants susceptible from flowering to maturity
• Management options: pathogen-free seed, susceptible varieties, crop rotation and fungicides
• Commonly confused with sunscald

Peronospora manshurica (Oomycete)

Photo Credit:

S. Markell, NDSU

FIGURE 1 – Discrete lesions top side of leaf

Photo Credit:

S. Markell, NDSU

A.

Photo Credit:

S. Markell, NDSU

FIGURE 2 – Fungal growth opposite lesions on underside of leaf (A) and the magnification of fungal growth (B)

Photo Credit:

D. Helland, Wilbur Ellis

FIGURE 3 – Severe infection

AUTHORS:Sam Markell and Dean Malvick

SYMPTOMS

• Lesions begin as discrete pale green to light yellow spots on top side of leaves
• Fluffy tan tufts of fungal growth occur opposite lesions on underside of leaves
• Lesions become brighter yellow and turn brown with age

FACTORS FAVORING DEVELOPMENT

• Frequent and prolonged periods of high humidity or free moisture (dew)
• Moderate temperatures
• Short crop rotation
• Planting infected seed or field history of downy mildew

IMPORTANT FACTS

• Yield loss thought to be rare; however, severe outbreaks have occurred in North Dakota and Minnesota
• Pathogen is specific to soybeans and will not cause downy mildew of other crops
• Can be confused with Septoria brown spot, powdery mildew and bacterial diseases

Cercospora sojina (fungus)

Photo Credit:

S. Markell, NDSU

FIGURE 1 – Lesions of various size and stages of development

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Spots and patterns of lesion development on leaf

Photo Credit:

S. Markell, NDSU

Photo Credit:

S. Markell, NDSU

FIGURE 3 – Upper and underside of lesion with fuzzy gray mold.

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Brown leaf spots surrounded by a darker reddish-brown or purple ring
• Centers of spots become tan as they age and develop black specks
• Spots may coalesce, fall out and kill large parts of leaves

FACTORS FAVORING DEVELOPMENT

• Warm and humid weather
• Highly susceptible soybean varieties

IMPORTANT FACTS

• Disease more common in southern areas of the Midwest
• Pathogen overwinters in infected soybean residue and seed
• Management options: crop rotation, tillage and fungicides
• Pathogen resistance to strobilurin (QoI, FRAC 11) fungicides is common in Minnesota and North Dakota
• Commonly confused with bacterial blight, Phyllosticta leaf spot and Septoria brown spot

Phyllosticta sojicola (fungi)

Photo Credit:

K. Bissonnette

FIGURE 1 - Gray irregular-shaped lesions with dark, narrow margins

Photo Credit:

K. Bissonnette

FIGURE 2 - V-shaped lesion with small black specs (pycnidia)

Photo Credit:

K. Bissonnette

FIGURE 3 - Large lesion with numerous pycnidia

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• May occur anytime in growing season
• Leaf lesions begin as pale green spots
• Lesions become gray to tan with narrow dark purple to brown margin
• Lesions may be oval, circular, irregular or V-shaped
• Small black specs (pycnidia) may appear in lesion centers
• Lesions also may occur on petioles, stems and pods

FACTORS FAVORING DEVELOPMENT

• Cool temperatures
• Wet conditions
• Short crop rotations
• Infected Seed

IMPORTANT FACTS

• Minor soybean disease that rarely impacts yield
• Appears to be uncommon in Minnesota and North Dakota
• Pathogen survives in infested crop residue and seed
• Commonly confused with frogeye leaf spot, bacterial blight, Septoria brown spot

Erysiphe diffusa and E. glycines (fungi)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – White tufts of fungal growth

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Severe infection covering leaf

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 3 – Infection spreading in hot spot

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Powdery white tufts of fungal growth on upper side of leaf
• Fungal growth may look like white flour sprinkled on the leaves
• Fungal growth can expand and may cover entire leaf surface
• Small black specs in growth may be observed late in season
• White fungal growth can be rubbed off leaf easily

FACTORS FAVORING DEVELOPMENT

• Temperatures from 64 to 75 F
• Low humidity with periods of limited leaf wetness
• Late-planted soybeans

IMPORTANT FACTS

• Yield loss is rare in Minnesota and North Dakota
• Usually occurs late in growing season
• The pathogen also may infect dry edible beans and field peas
• Commonly confused with downy mildew

Septoria glycines (fungus)

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 1 – Brown spots and chlorosis

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 2 – Trifoliate with brown spots and chlorosis

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 3 – Common pattern of symptoms developing in lower canopy

AUTHORS: Dean Malvick and Sam Markell

SYMPTOMS

• Dark brown spots (less than 1/8 inch diameter)
• Brown spots coalesce into large brown areas
• Irregular brown and yellow patches on one side of leaf
• Symptoms first develop in lower part of plant, then move up

FACTORS FAVORING DEVELOPMENT

• Wet and warm weather
• High plant density
• Continuous soybean planting
• Minimum tillage

IMPORTANT FACTS

• Typically does not cause yield loss
• Under severe conditions, defoliation and yield loss can occur
• Pathogen survives on infected residue and may be transmitted by seed
• Soybean varieties may vary in susceptibility
• Management options: crop rotation and fungicides
• Commonly confused with bacterial blight

Photo Credit:

A. Tenuta, OMAFRA, Ontario, Canada

FIGURE 1 – Leaf mottling and curling

Photo Credit:

A. Tenuta, OMAFRA, Ontario, Canada

FIGURE 2 – Discolored seed

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Light and dark green mottling of leaves
• Leaf puckering and downward curling
• Symptoms most severe on youngest leaves
• Flattening of pods, reduced seed size, seed discoloration and stunting may occur
• Infected plants can be asymptomatic

FACTORS FAVORING DEVELOPMENT

• Planting infected seed
• Aphid infestation

IMPORTANT FACTS

• Not thought to be common in Minnesota or North Dakota
• Virus is seedborne and aphid-vectored
• Commonly confused with herbicide injury and bean pod mottle virus

Phakopsora pachyrhizi (fungus)

Photo Credit:

S. Markell, NDSU

FIGURE 1 – Pustules visible on leaf wrapped around finger (approximately 5 to 10X)

Photo Credit:

S. Markell, NDSU

FIGURE 2 – Profuse sporulation and leaf chlorosis

Photo Credit:

D. Malvick, Univ. of Minnesota

FIGURE 3 – Magnified pustules

AUTHORS: Sam Markell and Dean Malvick

SYMPTOMS

• Very small gray-green, tan and/or red-brown spots on leaves
• Very small pustules on underside of leaf (hand lens needed)
• Leaf chlorosis and defoliation may occur

FACTORS FAVORING DEVELOPMENT

• Proximity to areas that do not freeze (southern Florida, Louisiana, Texas)
• Storms traveling from south to north that may bring spores showers (for example, hurricanes)
• Prolonged leaf wetness and moderate temperatures

IMPORTANT FACTS

• Soybean rust has never been recorded in Minnesota or North Dakota
• Dry edible beans may be a host
• Can cause significant yield loss
• Commonly confused with bacterial pustule and other foliar diseases.