Cercosporiosis

any one of several plant diseases caused by fungi of the genus Cercospora. The causative agents of cercospor-ioses are spread during vegetation; they winter in infected plant remains as clusters of thickened hyphae on the surface or in the upper layers of the soil. The most common and harmful cercosporioses are those of sugar beets, potatoes, and fruit crops (including grapes). Round or elongate ashen spots with a brown or red border form on the leaves, petioles, and stems of sugar beet and potato plants. Diseased potato leaves are covered with a gray-lilac coating and often wither. The dying of diseased parts of leaves causes a decrease in the yield of root crops, the sugar content of sugar beets, and the yield and starch content of potato tubers. The disease occurs in regions of sugar beet cultivation; it sometimes severely infects potatoes in the western regions of the nonchernozem zone of the USSR.

Control measures include clearing fields after sugar beets and potatoes are havested, isolating one-year-old sugar beet plantings from fields of seed plants, applying phosphorus and potassium fertilizers, and spraying with a 1-percent solution of bordeaux mixture or its equivalent two or three times.

In fruit crops spots varying in size, shape, and color form on the leaves; the spots contain the sporangia of the fungus. In grapes the affected leaves and berries fall. Control measures include destroying infected plant parts and fallen leaves, pruning the branches, and spraying with a 1-percent bordeaux mixture two or three times.