Title

Sunflower Disease Diagnostic Series

(PP1727, Reviewed Jan. 2018)
File
Summary

This series aids in disease identification.

Lead Author
Lead Author:
Samuel Markell, Extension Plant Pathologist, North Dakota State University
Other Authors

Robert Harveson, Extension Plant Pathologist, University of Nebraska; Charles Block, Plant Pathologist, USDA, Ames, IA; Thomas Gulya, USDA Sunflower Pathologist, (Retired), Fargo, N.D.; Febina Mathew, Field Crops Pathologist, South Dakota State Uninversity

Availability
Availability:
Available in print from the NDSU Distribution Center.

Contact your county NDSU Extension office to request a printed copy.
NDSU staff can order copies online (login required).

Publication Sections

Bacterial head rot

Pectobacterium carotovorum, subsp. carotovorum and P. atrosepticum

FIGURE 1 – Watery lesions forming on heads as a result of infection through wounds
FIGURE 1 – Watery lesions forming on heads as a result of infection through wounds
FIGURE 2 – Slimy masses of bacterial growth within infected head tissues
FIGURE 2 – Slimy masses of bacterial growth within infected head tissues
FIGURE 3 – Affected tissues dry out and turn black after a period of warm, dry weather
FIGURE 3 – Affected tissues dry out and turn black after a period of warm, dry weather

Bacterial head rot

Pectobacterium carotovorum, subsp. carotovorum and P. atrosepticum

AUTHORS: Bob Harveson, Sam Markell, Tom Gulya and Charlie Block

SYMPTOMS

• Coalescing lesions develop watery, soft-rot symptoms that become dark brown as disease progresses
• Heads give off an odor of rotting potatoes, and slimy masses of bacterial growth are present within infected tissues

FACTORS FAVORING DEVELOPMENT

• Thunderstorms with hail; insect or bird damage to heads
• Warm temperatures with high humidity levels

IMPORTANT FACTS

• Mechanical injury (from insects, birds or hail) is required for infection
• Pathogen is found ubiquitously in soil and is spread by rain splashing and driving winds
• More common in the U.S southern Great Plains states
• Can be confused with other head rot diseases (Sclerotinia, Botrytis or Rhizopus)

Rhizopus head rot

R. stolonifer, R. oryzae (syn. R. arrhizus) and R. microsporus

FIGURE 1 – Note wound from hail stone with subsequent development of watery, soft rot
FIGURE 1 – Note wound from hail stone with subsequent development of watery, soft rot
FIGURE 2 – Rotted area of head drying, shriveling and beginning to shred
FIGURE 2 – Rotted area of head drying, shriveling and beginning to shred
FIGURE 3 – Grayish fungal strands growing through head;
FIGURE 3 – Grayish fungal strands growing through head;
reproductive structures
reproductive structures

Rhizopus head rot

R. stolonifer, R. oryzae (syn. R. arrhizus) and R. microsporus

AUTHORS: Bob Harveson, Sam Markell, Charlie Block and Tom Gulya

SYMPTOMS

• First appears on heads as dark spots of varying sizes as a result of wounding, followed by a watery, soft rot that later dries and turns dark brown
• Rhizopus is distinguished from other head rots by the presence of grayish, threadlike mycelial strands within infected heads; small black reproductive structures the size of a pinhead also may be present

FACTORS FAVORING DEVELOPMENT

• Thunderstorms with hail; insect or bird damage on head
• Warm temperatures with high humidity levels

IMPORTANT FACTS

• Mechanical injury (from insects, birds or hail) is required for infection
• Pathogen is found ubiquitously in soil, and infective spores are released into the air easily
• More common in the U.S southern Great Plains states
• Can be confused with bacterial and/or Sclerotinia head rots

Sclerotinia head rot

Sclerotinia sclerotiorum

FIGURE 1 – Apothecia (grows from sclerotia and produces ascospores)
FIGURE 1 – Apothecia (grows from sclerotia and produces ascospores)
FIGURE 2 – Soft brown area on the back of head
FIGURE 2 – Soft brown area on the back of head
FIGURE 3 – A shredded sunflower with sclerotia
FIGURE 3 – A shredded sunflower with sclerotia

 

FIGURE 4 – White mycelium and black sclerotia on the face of a skeletonized sunflower head
FIGURE 4 – White mycelium and black sclerotia on the face of a skeletonized sunflower head

Sclerotinia head rot

Sclerotinia sclerotiorum

AUTHORS: Sam Markell, Tom Gulya, Charlie Block and Bob Harveson

SYMPTOMS

• Lesions begin as large, soft (mushy), brown areas on the back of heads that turn tan-cream, typically odorless
• White mold (mycelium) and hard black structures (sclerotia) form inside head
• Heads will shred, and disintegration and/or decapitation may occur

FACTORS FAVORING DEVELOPMENT

• Wet soils prior to bloom (facilitates apothecia production)
• Frequent wetness during or after bloom, including rain, fog, heavy dew
• Temperatures 85 F or below

IMPORTANT FACTS

• The same pathogen causes sclerotinia wilt and sclerotinia mid-stem rot
• The pathogen can survive for many years in the soil as sclerotia
• Management tools are limited
• Most common in the U.S. northern Great Plains
• Can be confused with Rhizopus head rot

Bacterial stalk rot

Pectobacterium carotovorum, subsp. carotovorum and P. atrosepticum

FIGURE 1 – Affected tissues blacken and are often on petiole axils
FIGURE 1 – Affected tissues blacken and are often on petiole axils
FIGURE 2 – Infected stalk splitting longitudinally
FIGURE 2 – Infected stalk splitting longitudinally

 

FIGURE 3 – Development of a foam on stalk wounds due to bacterial infection
FIGURE 3 – Development of a foam on stalk wounds due to bacterial infection

Bacterial stalk rot

Pectobacterium carotovorum, subsp. carotovorum and P. atrosepticum

AUTHORS: Bob Harveson, Charlie Block, Sam Markell and Tom Gulya

SYMPTOMS

• Infected stalks soften and dry up, becoming dark brown to black and may split open
• Plants often lodge under the weight of maturing heads
• A foam may appear on infected tissues as a result of bacterial-causing fermentation of sugars in plant

FACTORS FAVORING DEVELOPMENT

• Thunderstorms with hail
• Warm temperatures with high humidity levels

IMPORTANT FACTS

• Mechanical injury (from insects, birds or hail) is required for infection
• Pathogen is found ubiquitously in soil and is spread by rain splashing and driving winds
• More common in the U.S southern Great Plains states
• Can be confused with other stalk rots

Charcoal rot

Macrophomina phaseolina

FIGURE 1 – Gray lesion at the base of sunflower stalks
FIGURE 1 – Gray lesion at the base of sunflower stalks
FIGURE 2 – Microsclerotia inside sunflower stem
FIGURE 2 – Microsclerotia inside sunflower stem
FIGURE 3 – Stem with severe charcoal rot
FIGURE 3 – Stem with severe charcoal rot
FIGURE 4 – Field with charcoal rot
FIGURE 4 – Field with charcoal rot

 

Charcoal rot

Macrophomina phaseolina

AUTHORS: Sam Markell, Charlie Block, Bob Harveson and Tom Gulya

SYMPTOMS

• Gray to silver basal lesion starting at the soil line
• Premature senescence and plant death
• Abundant dusty black microsclerotia inside lower stem (visible with a hand lens)
• Vascular tissue compressed into layers

FACTORS FAVORING DEVELOPMENT

• Field history with charcoal rot, including soybeans, corn and other crops
• Wet weather in spring followed by hot, dry weather in reproductive growth stages
• Water stress (sandy soil, heat, drought, etc.)

IMPORTANT FACTS

• The same pathogen causes charcoal rot on soybeans, corn and other crops
• Infection begins early in the season but manifests in late reproductive stages if plants are stressed
• Most common in the U.S. southern and high Plains states
• Can be confused with Verticillium wilt and Sclerotinia wilt

Downy mildew

Plasmopara halstedii

FIGURE 1 – Stunting and chlorosis (yellowing) from systemic infection: Healthy (left), infected (right)
FIGURE 1 – Stunting and chlorosis (yellowing) from systemic infection: Healthy (left), infected (right)
FIGURE 2 – Underside (left) and upperside (right) of leaf with systemic infection
FIGURE 2 – Underside (left) and upperside (right) of leaf with systemic infection
FIGURE 3 – Local lesions from secondary infection
FIGURE 3 – Local lesions from secondary infection

Downy mildew

Plasmopara halstedii

AUTHORS: Sam Markell, Bob Harveson, Charlie Block and Tom Gulya

SYMPTOMS

• Stunting, leaf chlorosis, white sporulation on underside of leaf, plant death
• Horizontal heads when mature
• Secondary infection: discrete chlorotic leaf spots on upper leaf surface

FACTORS FAVORING DEVELOPMENT

• Cold soils and rainfall shortly after planting leading to waterlogged soil
• Cool nights with dew or rain (for local lesions via secondary infection)

IMPORTANT FACTS

• Secondary infections do NOT cause yield loss
• Pathogen is soil-borne and can survive many years in soil
• Disease is specific to sunflowers
• Fungicide seed treatments and resistant hybrids can be used for management
• Can be confused with herbicide damage

Fusarium root and stem rots

Fusarium species

FIGURE 1 – Pink discoloration caused by an unidentified Fusarium species
FIGURE 1 – Pink discoloration caused by an unidentified Fusarium species
FIGURE 2 – Pink streaks caused by Fusarium spp., associated with black microsclerotia of M. phaseolina (Charcoal rot)
FIGURE 2 – Pink streaks caused by Fusarium spp., associated with black microsclerotia of M. phaseolina (Charcoal rot)
FIGURE 3 – Sunflowers infected with Fusarium
FIGURE 3 – Sunflowers infected with Fusarium

Fusarium root and stem rots

Fusarium species

AUTHORS: Sam Markell, Bob Harveson, Charlie Block and Tom Gulya

SYMPTOMS

• Premature senescence
• Internal pink, orange, red or purple discoloration of pith

FACTORS FAVORING DEVELOPMENT

• Water stress (sandy soil, heat, drought, etc.)

IMPORTANT FACTS

• Many Fusarium species have been found to cause damage to sunflowers
• Many Fusarium species can cause disease and/or survive on crop hosts
• Economic damage is thought to be limited but can occur
• Frequently found with Charcoal rot
• Can be confused with other stalk/wilt diseases

Phoma black stem

Phoma macdonaldii

FIGURE 1 – Phoma lesions centered on petioles
FIGURE 1 – Phoma lesions centered on petioles
FIGURE 2 – A sunflower stalk with numerous Phoma lesions
FIGURE 2 – A sunflower stalk with numerous Phoma lesions
FIGURE 3 – Phoma (bottom black lesion) and Phomopsis (upper brown lesion) occurring on the same stem
FIGURE 3 – Phoma (bottom black lesion) and Phomopsis (upper brown lesion) occurring on the same stem

Phoma black stem

Phoma macdonaldii

AUTHORS: Sam Markell, Bob Harveson, Tom Gulya and Charlie Block

SYMPTOMS

• 1- to 2-inch black lesion, usually superficial
• Lesions centered on petioles
• Multiple lesions may occur on the same stem

FACTORS FAVORING DEVELOPMENT

• Frequent rainstorms
• Insects (such as stem weevils) can facilitate infection
• Sunflower residue nearby or short rotation

IMPORTANT FACTS

• Rarely economically important
• Typically the most common stem disease in the northern Great Plains
• Infection begins on leaves and progresses into the stem
• Can be vectored by black sunflower stem weevils (Apion)
• Can be confused with Phomopsis stem canker

Phomopsis stem canker

Diaporthe helianthi, D. gulyae

FIGURE 1 – Leaf bronzing
FIGURE 1 – Leaf bronzing
FIGURE 2 – Stem lesions at different stages of development
FIGURE 2 – Stem lesions at different stages of development

 

FIGURE 3 – Stem lesion and lodging
FIGURE 3 – Stem lesion and lodging

Phomopsis stem canker

Phomopsis helianthi, P. gulyae

AUTHORS: Sam Markell, Tom Gulya, Bob Harveson and Charlie Block

SYMPTOMS

• Leaf bronzing
• Large (often greater than 6-inches) brown stem lesion that is centered on petiole
• Stem will become hollow and is easily punctured with thumb
• Premature senescence and/or widespread lodging may occur

FACTORS FAVORING DEVELOPMENT

• Frequent rainstorms
• Infested sunflower residue nearby and short crop rotation

IMPORTANT FACTS

• Infection begins in leaves and spreads into the stem
• High disease pressure can devastate the crop
• Most common in the U.S. northern Great Plains
• Can be confused with Phoma black stem and Sclerotinia mid-stem rot

Sclerotinia mid-stem rot

Sclerotinia sclerotiorum

FIGURE 1 – Leaf lesion caused by Sclerotinia infected flower
FIGURE 1 – Leaf lesion caused by Sclerotinia infected flower
FIGURE 2 – Sclerotinia lesion with white mycelium
FIGURE 2 – Sclerotinia lesion with white mycelium
FIGURE 3 – Shredded stalk resulting in lodging
FIGURE 3 – Shredded stalk resulting in lodging
FIGURE 4 – Abundant small black sclerotia in a shredded stem
FIGURE 4 – Abundant small black sclerotia in a shredded stem

Sclerotinia mid-stem rot

Sclerotinia sclerotiorum

AUTHORS: Sam Markell, Charlie Block, Tom Gulya and Bob Harveson

SYMPTOMS

• Large (greater than 6-inch) tan to manila lesion on the stem, centered on petiole
• White mold (mycelium) and hard black structures (sclerotia) may be visible
• Stalk may shred at lesion, and plant eventually will lodge

FACTORS FAVORING DEVELOPMENT

• Wet soils before bloom (facilitates apothecia production)
• Temperatures 85 F or below
• Prolonged wet canopies (rain, fog, dew, etc.)

IMPORTANT FACTS

• The same pathogen causes Sclerotinia head rot and Sclerotinia wilt
• Infection begins on leaf when ascospores colonize senescent leaf tissue, florets or pollen
• Most common in the U.S. northern Great Plains states
• Can be confused with Phomopsis stem canker

Sclerotinia wilt/Basal stalk rot

Sclerotinia sclerotiorum

FIGURE 1 – Tan to manila basal lesion; note white mycelium
FIGURE 1 – Tan to manila basal lesion; note white mycelium
FIGURE 2 – Lodging and shredding (left plant only) caused by Sclerotinia wilt
FIGURE 2 – Lodging and shredding (left plant only) caused by Sclerotinia wilt
FIGURE 3 – Sclerotia and mycelium on infected sunflower
FIGURE 3 – Sclerotia and mycelium on infected sunflower
FIGURE 4 – Wilted sunflower plant
FIGURE 4 – Wilted sunflower plant

Sclerotina wilt/Basal stalk rot

Sclerotinia sclerotiorum

AUTHORS: Sam Markell, Bob Harveson, Charlie Block and Tom Gulya

SYMPTOMS

• Tan to manila basal lesion at soil line
• White mold (mycelia) and black sclerotia on basal lesion
• Whole-plant wilt, basal shredding and lodging may occur

FACTORS FAVORING DEVELOPMENT

• Field history with Sclerotinia diseases
• Tight crop rotation with broadleaf crops

IMPORTANT FACTS

• The same pathogen causes Sclerotinia white mold on other broadleaf crops
• Unlike Sclerotinia head and mid-stalk rot, fungus invades through roots
• Sclerotia can survive for many years in the soil
• Most common in the U.S. northern Plains states
• Can be confused with Verticillium wilt and Charcoal rot

Verticillium wilt

Verticllium dahliae

FIGURE 1 – Sunflower with Verticillium wilt. Note leaf chlorosis progressing upward.
FIGURE 1 – Sunflower with Verticillium wilt. Note leaf chlorosis progressing upward.
FIGURE 2 – Leaf symptoms
FIGURE 2 – Leaf symptoms
FIGURE 3 – Vascular browning
FIGURE 3 – Vascular browning
FIGURE 4 – External Verticillium lesion on lower stem (L) and shrunken and blackened pith (R)
FIGURE 4 – External Verticillium lesion on lower stem (L) and shrunken and blackened pith (R)

Verticillium wilt

Verticllium dahliae

AUTHORS: Sam Markell, Tom Gulya, Charlie Block and Bob Harveson

SYMPTOMS

• Interveinal chlorosis and necrosis starting at lowest leaves and progessing upwards
• Damaged vascular tissue; initially, a brown ring may be present
• Wilting occurring at bloom, usually in patches or rows
• Pith shrunken and black at maturity

FACTORS FAVORING DEVELOPMENT

• Water stress (sandy soil, heat, drought, etc.)
• Field history with Verticillium wilt

IMPORTANT FACTS

• The same pathogen causes Verticillium wilt on other crops (potatoes, etc.)
• Can be economically devastating with high disease pressure
• Leaf symptoms can be confused with Phomopsis stem canker
• Can be confused with Charcoal rot and Sclerotinia wilt

Albugo/White rust

FIGURE 1 – White sporulation on underside of leaf
FIGURE 1 – White sporulation on underside of leaf
FIGURE 2 – Chlorotic lesion on upper surface of leaf
FIGURE 2 – Chlorotic lesion on upper surface of leaf
FIGURE 3 – Dark, bruiselike lesion on the stem
FIGURE 3 – Dark, bruiselike lesion on the stem

Albugo/White rust

AUTHORS: Sam Markell, Tom Gulya, Bob Harveson and Charlie Block

SYMPTOMS

• Raised chlorotic pustules up to 3/8 inch in diameter on upper side of leaf
• Spores on underside of leaf opposite of chlorotic pustules
• Lesions on stem, petiole and head are dark and bruiselike

FACTORS FAVORING DEVELOPMENT

• Cool nights (50 to 60 F) and warm days (70 to 80 F)
• Rain splash

IMPORTANT FACTS

• Disease is very rare in the U.S.
• When found, it often is observed in single horizontal layer of leaves across a canopy
• Can be confused with downy mildew local lesions and powdery mildew

Alternaria leaf blight

Alternariaster helianthi, Alternaria zinniae

FIGURE 1 – Characteristic necrotic and chlorotic leaf blight lesions
FIGURE 1 – Characteristic necrotic and chlorotic leaf blight lesions
FIGURE 2 – Stem lesions
FIGURE 2 – Stem lesions
FIGURE 3 – Lesion coalescence and necrosis near leaf tips
FIGURE 3 – Lesion coalescence and necrosis near leaf tips
FIGURE 4 – Yellow leaf spots with little necrosis on resistant cultivar
FIGURE 4 – Yellow leaf spots with little necrosis on resistant cultivar

Alternaria leaf blight

Alternariaster helianthi, Alternaria zinniae

AUTHORS: Charlie Block, Sam Markell, Bob Harveson and Tom Gulya

SYMPTOMS

• Young leaf spots are small, dark, angular
• Leaf spots usually are found between major leaf veins, along leaf margins and tips and will coalesce
• Extensive yellowing (chlorosis) occurs, followed by browning and leaf death
• Defoliation occurs from the ground up
• Stem lesions are dark, narrow, elliptical and about ½ to 1½ inches long

FACTORS FAVORING DEVELOPMENT

• Rainfall shortly after planting
• Warm, humid weather

IMPORTANT FACTS

• Disease development is highly dependent on rain and dew
• Plants at flowering and seed filling stages more susceptible than young plants
• Fungus survives on plant residue
• Crop rotation and tillage of residue to encourage decomposition to help manage disease
• Can be confused with Septoria leaf blight, bacterial leaf spot

Apical chlorosis

Pseudomonas syringae pv. tagetis

Figure 1 - Young plant infected systemically; note bright yellow chlorosis and stunting
Figure 1 - Young plant infected systemically; note bright yellow chlorosis and stunting
FIGURE 2 – Plant nearing bud formation (R1) exhibiting systemic chlorosis symptoms
FIGURE 2 – Plant nearing bud formation (R1) exhibiting systemic chlorosis symptoms
FIGURE 3 – Distribution of apical chlorosis corresponding to low areas of water accumulation in field
FIGURE 3 – Distribution of apical chlorosis corresponding to low areas of water accumulation in field

Apical chlorosis

Apical chlorosis

Pseudomonas syringae pv. tagetis

AUTHORS: Bob Harveson, Tom Gulya, Sam Markell and Charlie Block

SYMPTOMS

• Distinctive bright yellow to nearly white chlorosis of newest leaves
• New leaves will be unaffected in warm weather
• May occur on isolated plants, patches or in rows
• Stunting if plants infected at a young stage

FACTORS FAVORING DEVELOPMENT

• Wet, cool conditions
• Water-logged soils

IMPORTANT FACTS

• Can be observed on plants of all growth stages, but most common on young plants (pre-bloom)
• Damage is minimal unless young plants are infected
• Chlorotic symptoms due to a toxin produced by the pathogen
• Related to bacterial leaf spot pathogen
• Can be confused with fertility problems, downy mildew and/or viruses

Bacterial leaf spot

Pseudomonas syringae pv. helianthi

FIGURE 1 – Multiple leaf spots surrounded by yellow halos
FIGURE 1 – Multiple leaf spots surrounded by yellow halos
FIGURE 2 – Small necrotic leaf spots on lower leaves
FIGURE 2 – Small necrotic leaf spots on lower leaves
FIGURE 3 – Coalescing of spots to form linear lesions
FIGURE 3 – Coalescing of spots to form linear lesions

Bacterial leaf spot

Pseudomonas syringae pv. helianthi

AUTHORS: Bob Harveson, Sam Markell, Tom Gulya and Charlie Block

SYMPTOMS

• Angular, necrotic spots of varying size
• Leaf spots form linear lesions that crack and fall out
• Necrotic spots may be surrounded with yellow haloes

FACTORS FAVORING DEVELOPMENT

• Wounds created by hail, sandblasting and other forms of mechanical damage
• Warm temperatures with high humidity levels

IMPORTANT FACTS

• Often is restricted to lower leaves and, thus, not generally economically damaging
• Can be seed-borne and soil-borne; spread by splashing rains and high winds
• Related to apical chlorosis pathogen
• Can be confused with Alternaria leaf blight and Septoria leaf blight

Powdery mildew

Erysiphe cichoracearum

FIGURE 1 – Discrete spots of white mycelium forming on a seedling
FIGURE 1 – Discrete spots of white mycelium forming on a seedling
FIGURE 2 – White spots forming on mature leaf (brown spots are rust)
FIGURE 2 – White spots forming on mature leaf (brown spots are rust)
FIGURE 3 – Sunflower leaf completely covered in mycelium
FIGURE 3 – Sunflower leaf completely covered in mycelium

Powdery mildew

Erysiphe cichoracearum

AUTHORS: Sam Markell, Tom Gulya, Bob Harveson and Charlie Block

SYMPTOMS

• White spots of fungal mycelium on upper leaf surface, can be rubbed off easily
• White mycelium will eventually cover the entire leaf
• Black specks (cleistothecia) may develop late in season

FACTORS FAVORING DEVELOPMENT

• High humidity
• Plant maturity and leaf senescence

IMPORTANT FACTS

• Usually doesn’t appear until after full bloom (R5)
• Symptoms are often more severe on lower leaves
• White fluffy growth on the top of leaves and late onset of disease help distinguish from downy mildew
• Can be confused with local lesions of downy mildew

Rust

Puccinia helianthi

FIGURE 1 – Pycnia (L) on upper side of leaf and Aecia (R) opposite pycnia on underside of leaf
FIGURE 1 – Pycnia (L) on upper side of leaf and Aecia (R) opposite pycnia on underside of leaf
FIGURE 2 – Uredinia surrounded by yellow halos; note spores on finger
FIGURE 2 – Uredinia surrounded by yellow halos; note spores on finger
FIGURE 3 – Pustules on stem and petiole (L) and bracts (R)
FIGURE 3 – Pustules on stem and petiole (L) and bracts (R)
FIGURE 3 – Pustules on stem and petiole (L) and bracts (R)

Rust

Puccinia helianthi

AUTHORS: Sam Markell, Bob Harveson, Charlie Block and Tom Gulya

SYMPTOMS

• Pycnia = yellow/orange bump on topside of leaf (early season)
• Aecia = cluster of orange cups opposite pycnia (early season)
• Uredia = dusty cinnamon-brown pustule (throughout season), spores can be easily rubbed off, yellow halo common
• Telia = hard black pustule (crop maturity)

FACTORS FAVORING DEVELOPMENT

• Frequent leaf wetness; dew, fog, light rain, etc.
• Temperatures between 55 and 85 F
• Proximity to wild, volunteer or sunflower residue that has or had rust

IMPORTANT FACTS

• Sunflower rust is specific to sunflowers (cultivated and wild)
• Economic losses can be devastating in epidemics
• Fungicide threshold = 1 percent severity on upper leaves at or before bloom (R5)
• Found in all U.S. Great Plains states
• Can be confused with soil splashed on lower leaves or other foliar diseases

Septoria leaf blight

Septoria helianthi

FIGURE 1 – Young developing lesions
FIGURE 1 – Young developing lesions
FIGURE 2 – Mature lesions of Septoria leaf spot
FIGURE 2 – Mature lesions of Septoria leaf spot
FIGURE 3 – Pycnidia visible as black specks inside large, round lesions (with hand lens)
FIGURE 3 – Pycnidia visible as black specks inside large, round lesions (with hand lens)

Septoria leaf blight

AUTHORS: Charlie Block, Bob Harveson, Sam Markell and Tom Gulya

SYMPTOMS

• Circular leaf spots up to ¾ inch in diameter, with dark margins and tan to gray centers
• Leaf spots often, but not always, surrounded by a narrow yellow halo
• Fungus survives on plant residue; infection spreads from bottom leaves upward
• Mature leaf spots become dotted with black specks, or pycnidia, on the upper leaf surface

FACTORS FAVORING DEVELOPMENT

• Cool temperatures and rain in the spring and fall
• Symptoms develop most rapidly after flowering, but finding leaf spots on seedlings is common
• Frequent wetness during or after bloom, including rain, fog and heavy dew

IMPORTANT FACTS

• Disease tends to go dormant during hot, dry weather
• Seldom a problem in drier sunflower-production areas
• Can be confused with Alternaria leaf blight and bacterial leaf spot. Larger rounded lesions with pycnidia help distinguish Septoria leaf spot from Alternaria leaf spot.

Virus Diseases

Nebraska mottle/ringspot virus? Sunflower mosaic virus

FIGURE 1 – Greenhouse-inoculated seedlings showing small, yellow spots (NMRV?)
FIGURE 1 – Greenhouse-inoculated seedlings showing small, yellow spots (NMRV?)
FIGURE 3 – Typical sunflower mosaic virus symptoms (SMV)
FIGURE 3 – Typical sunflower mosaic virus symptoms (SMV)

Virus Diseases

Nebraska mottle/ringspot virus? (NMRV?)Sunflower mosaic virus (SMV)

AUTHORS: Tom Gulya, Bob Harveson, Sam Markell and Charlie Block

SYMPTOMS

NMRV?

• Begins as small, yellow spots on new foliage
• Chlorotic ringspots may develop as plants mature

SMV

• Leaf mosaic symptoms

FACTORS FAVORING DEVELOPMENT

• Unknown

IMPORTANT FACTS

• Viruses are not typically an economic problem due to low incidence
• Identity of virus pathogen and potential vectors are unknown in many viruses
• Sunflower mosaic virus can be seedborne and vectored by aphids