Before grafting citrus, it is important to sterilize grafting tools to both kill any pathogens that may harm grafts and also to kill diseases of citrus that are readily spread via grafting. Likewise it is important to sterilize pruning tools to avoid the spread of diseases when pruning.
Chlorine Bleach is the Best Disinfectant
Chlorine bleach is the disinfectant used by the scientists at the CCPP whose mission is to make disease-free citrus budwood available to growers. A readily available product with an adequate concentration of bleach to kill all citrus pathogens is Clorox Clean-Up. I am now using Clorox Clean-Up to disinfect my tools when grafting and pruning citrus.
Chlorine bleach can be hazardous and should be used with care. When spraying it is important to avoid exposure to the spray or mist. The material safety data sheet from Clorox recommends the use of safety glasses and recommends immediate rinsing of exposed skin with water. It can ruin clothes, so wearing old clothes would be advisable. It is also corrosive to tools; to minimize the corrosive effect on tools, it is a good idea to wash tools and then spray with WD-40 after grafting.
When spraying grafting tools, be sure to spray to the point that the bleach is dripping off of the tools as shown below. After spraying all of the tools, repeat by again spraying them all to the point that the bleach is dripping.
When disinfecting with Clorox Clean-Up, Clorox recommends that the surface remain wet for 30 seconds before rinsing and wiping clean.
After grafting, wash tools and spray with WD-40 to make the tools last longer.
Lysol is an Alternative Disinfectant
With all of the warnings about using bleach, there will be some who will be reluctant to use it. One alternative is Lysol Disinfectant Spray. Lysol is less hazardous to people, clothes, and tools. Unfortunately it would also seem less hazardous to pathogens and I know of no science regarding its use in citrus grafting. Lysol recommends that a surface remain wet for 10 minutes to disinfect. 10 minutes is a long time to wait and that makes Lysol less practical, but it is certainly better than no disinfectant at all.
When using Lysol, be sure to spray tools to the point that the Lysol is dripping off of them. After spraying all of the tools, repeat by again spraying them all to the point that they are dripping.
Disinfecting Wipes are a Less Preferred Disinfectant
Yet another alternative is a disinfecting wipe like Clorox Disinfecting Wipes. To disinfect, Clorox recommends that the surface remain visibly wet for 4 minutes. I tried this and found it difficult to achieve in practice as the disinfectant evaporated from the tools in seconds, not minutes. Because of this, I do not recommend disinfecting wipes. Disinfecting wipes would be better than no disinfectant at all, however.
Alcohol is used to Preserve Citrus Pathogens
Yet another alternative is to spray tools with 70% isopropyl alcohol. When I admitted to using this approach, Georgios Vidalakis of CCPP pointed out to me that they use alcohol in the lab to preserve some citrus pathogens. Clearly alcohol is not the best choice for disinfecting tools for citrus grafting! Alcohol does kill some pathogens, however, so again it is better than using nothing at all. I have now switched to using Clorox Clean-Up to sterilize my grafting tools. Another potential use for alcohol is to clean the rootstock itself if top working with a dirty rootstock. Unlike the other disinfectants, alcohol will not harm the tree. Alcohol will not kill mold spores, however.
Thank you very much to Rock Christiano and Georgios Vidalakis of CCPP for helping me in the preparation of this article.