“GUMMOSIS” OR “DIEBACK” OF APRICOTS
The first record of the occurrence of E. armeniacae in Europe was obtained in 1963 when apricot trees in the south of France were found to be commonly affected (Carter, Morvan and Castelain3). Dieback of several species of the ornamental shrub Ceanothus in South Australia was reported by Moller5 to be caused by the same fungus, and in California, a dieback of western choke-cherry (Prunus virginiana var. demissa (Torr. & Gray.) Torr.) has been attributed to E. armeniacae by English and Davis4.
In recent visits to the Bas-Rhône district of south-east France (Carter) and to California (Moller) we found the ascigerous stage of the pathogen on dead wood of grape vine (Vitis vinifera L.) in the vicinity of apricot orchards where it undoubtedly contributes inoculum for their infection. The amount of infection in 5—6 year old apricot trees in plantations of the Compagnie du Bas-Rhône et Languedoc and in older apricot trees in the San Francisco bay area of California appeared to be as high as in some of the worst-affected districts of South Australia. We believe that situations similar to this must surely occur in other parts of Southern Europe, but we have not had the opportunity of visiting other European regions of apricot production to confirm our belief.
Air sampling close to a source of E. armeniacae ascospores in five consecutive years has shown that there is a regular seasonal cycle of ascopore output from stromata of this pathogen under South Australian conditions. This quantitative study has revealed a winter period of low ascospore liberation which coincides closely with the dormant period of the apricot host. Airborne spores are abundant whenever rain falls during spring, summer and autumn (September to April in Southern Australia) (Moller & Carter7).
Apricot tree pruning experiments based on these findings have been reported (Moller6 Carter & Moller2. Significantly less infection takes place when trees are pruned immediately after spore dispersal declines (early winter) than when trees are pruned in autumn or spring, but nevertheless 3% of small wounds (< 1.3 cm. diam.) and 12% of large wounds