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Powdery Mildew

Typical powdery mildew leaf symptoms




Sugar Beet, beetroot.


A white/light grey mould of fungal mycelium and spores develops on the leaf surface, usually between August and October. Resting spores appear as small black dots on infected leaves. Leaves ultimately turn yellow and die. Conidiophores (specialised hyphae) release conidia (asexual spores) which further disperses the inoculum within the crop or to neighbouring fields, ascospores (sexual spores) are released later in the season when conditions are unsuitable for production of conidia. Overwinters as mycelia on wild beet, groundkeepers or beet volunteers.


The disease initially occurs on isolated plants, but can quickly spread throughout the whole field. The mould reduces leaf photosynthesis and accelerates leaf senescence, which subsequently reduces root yields.

Favourable Factors

Suitable conditions for disease establishment are dry weather and high temperatures (20C optimum) with dew at night. The annual forecast of the likely disease pressure for the newly sown crop is based on the number of frosts in February and March. Cold winters with frequent frosts are unfavourable for disease development.


Substantial yield losses. Sugar yield may be reduced by up to 30%.


Identification and Management of sugar beet diseases

Find out more information on the key disease threats to your sugar beet crop. For each disease you will find out the importance of the disease in terms of potential yield penalty, how to identify the disease in its early stages and our advice on the best control strategies.

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