Damage usually patchy, not uniform throughout field. Early blooms are produced on long, strong, single stems. Larger rounded lesions with pycnidia help distinguish Septoria leaf spot from Alternaria leaf spot. The red stems are probably sunburns too. This is quite possibly what you are seeing in your sunflowers. carotovorum and P. atrosepticum, 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 3 – Affected tissues dry out and turn black after a period of warm, dry weather, AUTHORS: Bob Harveson, Sam Markell, Tom Gulya and Charlie Block, • 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, • Thunderstorms with hail; insect or bird damage to heads• Warm temperatures with high humidity levels, • 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), R. stolonifer, R. oryzae (syn. )Sunflower mosaic virus (SMV), AUTHORS: Tom Gulya, Bob Harveson, Sam Markell and Charlie Block, • Begins as small, yellow spots on new foliage• Chlorotic ringspots may develop as plants mature, • 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. R. arrhizus) and R. microsporus, 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. )• 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, FIGURE 1 – White sporulation on underside of leaf, FIGURE 2 – Chlorotic lesion on upper surface of leaf, FIGURE 3 – Dark, bruiselike lesion on the stem, • 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, • Cool nights (50 to 60 F) and warm days (70 to 80 F)• Rain splash, • 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, Alternariaster helianthi, Alternaria zinniae, FIGURE 1 – Characteristic necrotic and chlorotic leaf blight lesions, FIGURE 3 – Lesion coalescence and necrosis near leaf tips, FIGURE 4 – Yellow leaf spots with little necrosis on resistant cultivar, AUTHORS: Charlie Block, Sam Markell, Bob Harveson and Tom Gulya, • 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, • Rainfall shortly after planting• Warm, humid weather, • 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, AUTHORS: Bob Harveson, Tom Gulya, Sam Markell and Charlie Block, • 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, • Wet, cool conditions• Water-logged soils, • 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, FIGURE 3 – Coalescing of spots to form linear lesions, • Angular, necrotic spots of varying size• Leaf spots form linear lesions that crack and fall out• Necrotic spots may be surrounded with yellow haloes, • Wounds created by hail, sandblasting and other forms of mechanical damage• Warm temperatures with high humidity levels, • 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, FIGURE 2 – White spots forming on mature leaf (brown spots are rust), FIGURE 3 – Sunflower leaf completely covered in mycelium, • 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, • High humidity• Plant maturity and leaf senescence, • 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, 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 3 – Pustules on stem and petiole (L) and bracts (R), • 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), • 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, • 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, FIGURE 2 – Mature lesions of Septoria leaf spot, FIGURE 3 – Pycnidia visible as black specks inside large, round lesions (with hand lens), AUTHORS: Charlie Block, Bob Harveson, Sam Markell and Tom Gulya, • 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, • 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. 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