Grape Black Measles




Grapevine measles, also called esca, black measles or Spanish measles, has long plagued grape growers with its cryptic expression of symptoms and, for a long time, a lack of identifiable causal organism(s). The name ‘measles’ refers to the superficial spots found on the fruit (Fig. 1). During the season, the spots may coalesce over the skin surface, making berries black in appearance. Spotting can develop anytime between fruit set and a few days prior to harvest. Berries affected at fruit set tend not to mature and will shrivel and dry up. In addition to spotting, fruit affected later in the season will also have an acrid taste.

Leaf symptoms are characterized by a ‘tiger stripe’ pattern (Fig 2-bottom leaf) when infections are severe from year to year. Mild infections can produce leaf symptoms (Fig. 2-upper leaf) that can be confused with other diseases or nutritional deficiencies. White cultivars will display areas of chlorosis followed by necrosis, while red cultivars are characterized by red areas followed by necrosis. Early spring symptoms include shoot tip dieback, leaf discoloration and complete defoliation in severe cases.

Management

Presently, there are no effective management strategies for measles. Wine grape growers with small vineyards will often have field crews remove infected fruit prior to harvest. Raisins affected by measles will be discarded during harvest or at the packing house, while table grape growers will leave affected fruit on the vine. Current research is focused on protecting pruning wounds from fungal infections to minimize suspect fungi from colonizing fresh wounds.



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