Effect of a traditional control method (tree removal) on the spread of sharka in an apricot orchard in Southeastern Spain

Abstract

The spatial spread of sharka disease (Plum pox virus, PPV) was studied from 1990 to 2002 in a traditional apricot (Prunus armeniaca L.) orchard located in Murcia (Southeast of Spain). The occurrence of sharka was determined by the visual observation of symptoms on leaves and fruits during the ripening stage, when symptoms are most visible. To ascertain PPV in doubtful samples, an ELISA-DASI assay was applied to the leaves. All trees infected the previous year were pulled up and were not replanted. Results showed that the virus was introduced to the farm by natural vectors (aphids) from a neighbouring sharka-infected plum orchard. It was then transmitted from these infected trees mainly to nearby trees by the same vectors, although also often to trees standing quite a distance away. The long interval between infection and symptom appearance makes eradication of the disease more difficult. Pulling up infected trees as a control method reduced the percentage of trees ultimately lost, and over the long term could stop the further spread of the disease.