A gardening friend of mine told me that I should be disinfecting my tools whenever I am out in the garden pruning this winter. Is this really necessary?

The purpose of disinfecting tools is to avoid transferring disease-causing bacteria or spores from an infected branch to another branch or another plant. It is most important to disinfect tools during the growing season and whenever you are working on a diseased plant.

In winter, when plants are dormant and many disease pathogens are not present, I seldom see a need to disinfect pruning tools while doing routine pruning. However, it depends on the plant and the likely disease.

For example, fire blight bacteria, which infect trees like crab apples, apples, pears and hawthorns, do not overwinter in the trees' vascular system, making it unlikely that you would transfer this disease when pruning during the winter dormant season. However, if you prune fire blight-infected plants during the growing season, you should disinfect your tools after every pruning cut.

Even in winter, you should disinfect your tools when pruning red-twig dogwoods, which often have twig blight. This disease is easy to spot because of brown to black areas on the stems, and the best solution is to prune these stems out. Because the fungal spores that cause this disease can overwinter, you should disinfect your pruning tools between plants, if not between branches.

In order to know for certain when you need to be vigilant about disinfecting tools, you would need to know what type of plant you are working with, whether it is prone to a disease and what signs would show an infection, what the pathogen is that causes the disease and its life cycle. If you are not familiar with plant diseases, the safest practice is to disinfect your tools at least once or twice a day whenever you are pruning.

Diseases are more likely to be spread when pruning in cool and wet conditions, so try to prune on sunny, dry days if you are concerned about spreading a disease.

Among the types of diseases that are easily transmitted by pruning tools are those that invade the vascular system of plants or form oozing cankers. In general, it is a good idea to disinfect your tools when working in garden areas where there are diseases caused by viruses, viroids, vascular fungi or bacteria.

Avoid cutting through any active, oozing cankers, as the sticky material they ooze is often difficult to remove from pruner surfaces, and disinfectants tend not to be entirely effective against it. The best practice is to cut in healthy wood that is well below the canker or wait until the canker has dried.

Do not apply any disinfectant directly on pruning cuts, because that can damage plant tissue.

Research comparing disinfecting solutions has produced mixed results. Generally any disinfectant will remove viruses or viroids from tools, but removal of other pathogens such as canker bacteria is less certain.

I find that Lysol disinfectant spray is effective and very easy to use in the field. A solution of bleach and water often is suggested as a disinfectant, but I do not recommend it. The bleach can damage your clothes and irritate your skin and it also is corrosive and very hard on tools. Tools that are pitted or corroded are difficult to disinfect thoroughly.

Tim Johnson is director of horticulture for the Chicago Botanic Garden in Glencoe; ctc-realestate@tribune.com.