Cercospora leaf spot is the most serious beet disease in Greece and other countries because it destroys the plants causing significant losses in weight and sugar content. In Greece the damage can reach 40-50% of sugar production.
Scientific name: Cercospora beticola
Other names: Black mold, Okra leaf spot
Greek name: Κερκόσπορα των Τεύτλων
In late May-early June, depending on plant growth and weather conditions, small grey-brown spots appear on the leaves, with a reddish-brown margin, which slowly multiply and eventually dry out the entire leaves. In wet weather, black spots and a greyish-white fuzz (fruit spores and spores of the pathogen) appear in the center of the spot, particularly on the lower surface of the leaves.
In late July-late August the field looks like burnt. The plants put out new leaves (regrowth), consuming sugar stored in the root.
Pathogen – Growth conditions
Cercospora leaf spot disease is caused by the fungus Cercospora beticola. The fungus perpetuates itself in the form of microspores and spores (conidia) on the leaves or on the seed. Infection starts when the spore (conidia) of the pathogen germinates on the leaf in wet and warm weather. The mycelium then enters the leaf through the stomata and the fungus grows inside the leaf. The spores (conidia) are spread by rain and cause disease to surrounding plants.
The high humidity in the leaf area of the plants and a temperature of 25-30 degrees Celsius favor the growth and spread of the disease. Therefore, rainfall from mid-May onwards, after the beet rows have closed, and watering – especially with artificial rain – create particularly dangerous conditions.
The main means of effectively controlling the disease is the application of an appropriate spray program with specialized powder mildew fungicides. In areas of particular risk, disease resistant varieties such as Greek Vergina and others are used. In addition, rational irrigation and crop rotation are recommended.