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Cercospora leaf spot

Causal agent: Cercospora beticola
Symptoms: Small, relatively circular lesions (2-3 mm), in the centre bright grey encircled with a reddish-brown margin. As the disease progresses individual spots coalesce resulting in the death of large parts of the leaf blade and finally causing the wilting of numerous leaves. Under a magnifying glass a grey mycelium with black dots (conidiophores) is visible. Symptoms of the damage are first observed only on single plants, their spreading over the whole field is transmitted by rain-splash and wind.
Epidemiology: Conidia of the fungus persist in infected leaf debris. Under close crop rotations (short intervals between beet crops) the potential for infection from the soil is increased. Symptoms are observed within 5 days with a relative humidity of at least 96 % and temperatures of 23-27 C. The infection occurs mainly during damp and warm weather.
Risks: When the crop meets across the rows, the microclimate in the field changes and there is a high potential of infection from the preceding years (narrow crop rotation) and by the use of irrigation
Economic importance: Cercospora is one of the most important foliar diseases of sugar beet in all humid and warm growing areas. This noxious fungus can contribute to high yield losses in many countries worldwide.
Control: Agrochemicals are available, at present contact and systemic fungicides as well as copper products are allowed. An indirect control can be carried out by the choice of resistant varieties and the cultivation of beet in crop rotations of at least three years.

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