The research work under discussion in this article is not yet completed but certain tentative conclusions have been reached which may be of interest.
Bud death and lateral wilt in raspberries have been well-known to Scottish fruit growers for many years under the blanket heading of raspberry die-back. However, we refrain from using this term because it can cover several disorders of similar effect, including frost damage, spur blight and cane spot. We now specifically recognise two distinct syndromes, bud death and lateral wilt, both associated with one fungus, Fusarium avenaceum.
Raspberry bud death has been observed frequently and preliminary investigations were done at the East of Scotland College of Agriculture in the 1950s by Dr A. E. W. Boyd. The main conclusions to be drawn from this work are that two species of the fungus Fusarium were usually involved and that pathogenicity tests with one of them (Fusarium acuminatum) proved negative. Our work at the Mycology Section of the Scottish Horticultural Research Institute centres on the other species, Fusarium avenaceum.
F. avenaceum may be readily cultured from the soil where, as spores, it seems able to survive for relatively long periods. Spores are also formed in orange pustules on the canes and are dispersed by rain splash. We have often cultured the fungus in the spring from buds and, later in the year, from fruiting laterals and canes which have wilted during the summer. It now seems likely that spring bud death and summer wilting may be classed as distinct diseases, though both are associated with the fungus F. avenaceum.