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Mycologia, DEUTEROMYCOTINA, HYPHOMYCETALES, DEMATIACEAE .

Crops attacked: sunflower .

Leaf spot

Identification, Description, Biology, Epidemiology, Treatement, Possible misleading, Images

[R]Description
Brown little leaf spots (of a few milimeters diameter) to be found both on and between the leaf veins. The spots look brown and striated on the petioles but they appear black, striated and of an elliptical shape on the stem ; on the non-floral side of the capitulum there are brown round spots (about 1 cm diameter) with a slight depression in the center.

[R]Biology
The mycelium rests in the plant debris covering the soil and less frequently on seeds. Its conidia are spread by the wind and the water.
Splashing of conidia affect the lower levels of the leaf first. The leaf spots resulting from this primary infection will sporulate and produce new conidia which are then spread to the whole foliage and will contaminate new plants causing a general epidemic on that parcel.

[R]Epidemiology
High temperature (24 to 27 °C.) and frequent rain (free water or dew absolutely necessary for a few hours) alternating with periods of dryness are favorable to the sporulation of the fungus.
Wind facilitates the spreading of the fungus.

[R]Treatement
Destruction of the culture debris.
Avoid the too frequent return of the sunflower in the rotation.
Practice seed control to avoid damping-off of the seedlings (rare in Europe).

[R]Possible misleading
The leaf spots caused by Septoria helianthi but no spot on the veins in case of septoria disease.

[R] Images

1. Alternaria helianthi , Alternaria leaf spots (LAMARQUE C., INRA)
   Sunflower alternaria leaf spots Alternaria helianthi spots on sunflower capitulum.
   
2. Alternaria helianthi , Alternaria leaf spots (LAMARQUE C., INRA)
   Sunflower alternaria leaf spots Alternaria helianthi spots on the lower surface of sunflower capitulum.
   
3. Alternaria helianthi , Alternaria leaf spots (LAMARQUE C., INRA)
   Sunflower alternaria leaf spots Alternaria little spots on sunflower capitulum.
   
4. Alternaria helianthi , Alternaria leaf spots (LAMARQUE C., INRA)
   Sunflower alternaria leaf spots Alternaria helianthi spots on sunflower stems.
   
5. Alternaria helianthi , Alternaria leaf spots (LAMARQUE C., INRA)
   Sunflower alternaria leaf spots Spots of Alternaria helianthi on a leaf and petiole of a sunflower.
   
6. Alternaria helianthi , Alternaria leaf spots (LAMARQUE C., INRA)
   Sunflower alternaria leaf spots Conidia of Alternaria helianthi demonstrating variability in form.
   

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