I co-authored a pruning leaflet about eight years ago which has been a popular guide for woodland owners, managers and others who care for trees (see previous post). However, there was a serious omission in the leaflet that has prompted an update: the importance of sterilising tools between trees, and between sites to reduce the risk of spreading infection.
The importance of phytosanitary control is now paramount, with the apparent increase in serious outbreaks of pests and diseases affecting our trees, such as Phytophthora ramorum (Sudden Oak Death) [apologies for incorrectly stating Acute Oak Decline in a former draft]. Knowledge about the impact on disease spread from pruning has existed for over a century: in the USA Waite and Smith (1906) linked fire blight (Erwinia amylovora Burrill) infections in plant nurseries to contaminated pruning tools. More recently Goodman and Hattingh (1988) reported a 66% infection rate in trees pruned with secateurs treated with bacterial spot (Xanthomonas campestris pv. pruni Smith), although interestingly infection rates were only this high during cool and wet conditions. The worst case of infection spread will come from pruning weeping bacterial wounds, e.g. cankers, where extreme care should be taken to clean tools after use – better still, wait until the oozing has dried up before pruning. There is some evidence that even the best cleaning methods are ineffective at removing bacteria from the surfaces of cutting tools (Kleinhempel et al. 1987).
The following action is recommended on sites where there is a biosecurity problem but I would go further suggest that it is good practice to follow these recommendations at all times.
Sterilise pruning tools between use on each tree by wiping with a cloth soaked in industrial methylated spirits (IMS). You should also complete a more thorough sterilisation between sites, by soaking your tools in IMS.
Some suggest using household bleach, perhaps diluted nine parts water to one part bleach. However, be aware that bleach is extremely toxic to plants, will ruin your clothes if splashed or dripped onto them, and it is a corrosive that will also spoil your tools.
After a hard day’s work in the garden or woods, and following disinfecting your tools using IMS as recommended above, rub some vegetable oil over the metal parts to keep your pruning tools in perfect working order.
The pruning leaflet is published by Woodland Heritage and available along with other practical leaflets from their website.
Goodman, C.A. and M.J. Hattingh, 1988. Mechanical transmission of Xanthomonas campestris pv. pruni in plum nursery trees. Plant Disease. 72:643. (link)
Kleinhempel, H., M. Nachtigall, W. Ficke and F. Ehrig. 1987. Disinfection of pruning shears for the prevention of the fire blight. Acta Horticulturae. 217: 211-218.
Waite, M.B. and R.E. Smith. 1906. Pear blight – its introduction, cause and treatment, and work of eradication. Californian State Horticultural Committee Special Report, 27 pp.