HNS 71: Bacterial disease of HNS - Chemical control

Eight commercial nurseries located in six regions were visited on separate occasions during a period of approximately one year. At each nursery, stock was examined for symptoms typical of bacterial disease, and samples collected for laboratory examination. Samples were examined microscopically and attempts made to isolate the pathogen onto agar plates. Suspected pathogens were then identified as far as possible within the limitations of time available. 

A total of 220 samples of suspected bacterial diseases representing 39 genera were collected and examined in the laboratory. Suspected bacterial pathogens were isolated from 117 of the samples representing twenty-one genera. Records of bacterial diseases in an additional eleven genera were also obtained from ADAS Plant Clinic, Wolverhampton and SAC Crop Health Centre. The ten most prevalent diseases are shown in Table I. 

The majority of the diseases were caused by strains of Pseudomonas syringae. In some cases, the pathogen has been presumptively assigned to a distinct pathovar (pv.). In effect this means that the pathogen can't infect other hosts (e.g. pv. philadelphi only infects Philadelphus, pv. berberidis only infects Berberis). In most cases, however, the pathogen has not been assigned to a pathovar and it is not known whether these strains can infect other hosts. Some of the diseases found have not previously been recorded in the scientific literature. 

MAFF has already been funding work on shot-hole of cherry laurel and these results clearly support a need for it to continue. It is hoped that this may serve as a model system to identify control strategies which can then be applied to other similar diseases. Xanthomonas leaf spot of ivies was also widespread and causing considerable concern to growers. In common with many of these diseases, there is very little known about it, and as the pathogen belongs to a different genus, it presents an ideal secondary target for future research effort

There is a wide range of bacterial diseases of hardy nursery stock (HNS), but most have been little studied. Reports of losses and problems caused by bacterial diseases of HNS appear to have increased over the last few years. These diseases do not appear to be controlled effectively using currently approved chemicals and there are no definitive guidelines for their control. There has therefore been an increasing demand for "something to be done". 

Inevitably due to the diversity of crop species in the sector, it is difficult to obtain reliable inf01mation on the prevalence and importance of different diseases, and therefore difficult to define targets for research. This project was therefore aimed at obtaining accurate and reliable data on the extent of and importance of the different bacterial diseases in HNS to distinguish real from perceived problems and to allow targeting of future research. It was intended as a first step in the development of a programme of research targeted towards improving our understanding and knowledge-base for bacterial diseases of HNS with the ultimate aim of devising effective control strategies.