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Mycologia, DEUTEROMYCOTINA, HYPHOMYCETALES, DEMATIACEAE .

Crops attacked: sugar beet .

Cercospora disease

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

[R]Description
Small leaf spots (4-5 mm diameter) with grey necrotic center and red margins.
The spots develop and multiply causing severe dehydratation of the lamina starting with the marginal leaves and progressing to the destruction of the entire crop foliage.
Black microscopic fructifications occur on the leaf spots on the abaxial surface.
The decay of the foliage and the new shoots the plant puts forth in response to the disease cause important loss of weight and sugar quality.
The seed crops are also invaded by spots from the base of the plant up to the bracts and seeds.

[R]Biology
The fungus survives as pseudo-sclerotia and conidia on seeds and crop debris.
As this is a systemic fungus one single conidium germinating on a leaf is enough to infect the whole plant. A few days after the contamination occurs the first spots show on the leaves and dark conidiophores carrying new conidia form on the abaxial surface.

[R]Epidemiology
The disease starts with a limited infection court affecting a few plants and develops into an epidemic which extends to the whole field.
Conidia are spread by rain and splash.
Humidity (RH >90%) allows conidial germination to take place and heat (temperature over 17 °C. with optimum at 27 °C.) facilitates the growth of the fungus.

[R]Treatement
Treatment of the seeds (glomerula) in the seed crops during the vegetative cycle.
Avoid the short beet crop rotations.
Use resistant cultivars.
If fungicide treatment is applied, it has to be carried out between the germination of the spores on leaves and their actual penetration into the leaf parenchyma (they persist in the sub-stomatal cavities for 3-5 days).
Parasitic resistant strains to common fungicides have appeared.

[R]Possible misleading
Possible confusion with the spots of Ramularia beticola whose chains of white spores are arranged in white cushions.

[R] Images

1. Cercospora beticola , Cercospora disease (INRA)
   Beet cercospora disease Generalised infection of beet by cercospora disease.
   
2. Cercospora beticola , Cercospora disease (INRA)
   Beet cercospora disease Wilt of the crown leaves infected by cercospora disease.
   
3. Cercospora beticola , Cercospora disease (BASF)
   Beet cercospora disease Heavy infection of cercospora disease on a beet leaf : little primary spots are coalescing.
   
4. Cercospora beticola , Cercospora disease (INRA)
   Beet cercospora disease Grey round spots of cercospora disease surrounded by a brown red margin on a beet leaf (general view of a leaf).
   
5. Cercospora beticola , Cercospora disease (INRA)
   Beet cercospora disease Grey round spots of cercospora disease surrounded by a brown red margin on a beet leaf (detail of a lonely spot).
   
6. Cercospora beticola , Cercospora disease (PUTZ C., INRA)
   Beet cercospora disease View of damage due to leaf spot on a chlorotic beet leaf.
   

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