When discussing plant diseases and their management, I often emphasize decontaminating pots, gardening tools and work surfaces as one part of a successful disease management strategy. To kill fungi and bacteria (and to a lesser extent viruses) I often recommend treating items for at least 30 seconds with alcohol, commercial disinfectants, or bleach.
When using alcohol, a 70% solution is optimal for decontamination. I use ethanol for decontaminating items in my lab, but rubbing (i.e., isopropyl) alcohol is a better option for home gardeners, as it is readily available at a local drugstore or grocery store. Rubbing alcohol is formulated as a 70% solution and can be used straight out of the bottle.
Commercial disinfectants come in many forms. I look for products that contain alcohol (you may see ethanol listed as an ingredient) and where the percentage of all active ingredients is as close to 70% as possible. If you opt to use a spray disinfectant, spray items until they drip and then allow them to air dry.
Bleach is probably the most challenging material to use for decontamination. Back when I started at the PDDC (almost 25 years ago), most bleach that you could buy at the grocery store was formulated to be 5.25% sodium hypochlorite (the active ingredient), and you just had to make a 10% solution (i.e., 1 part bleach and 9 parts water) to yield an approximate 0.5% solution that is optimal for decontaminating items. Nowadays, the bleach that you buy can contain very different concentrations of sodium hypochlorite (e.g., 1.8%, 5.25%, 7.5%, 8.25%), and you have to be more careful how you mix up your dilute bleach solution.
Here are some easy instructions on how to dilute the bleach that you buy (assuming it contains 1% or more sodium hypochlorite) to properly to yield a solution that is 0.5% sodium hypochlorite (or slightly higher):
- Find the percentage of sodium hypochlorite in your bleach in the ingredient list;
- Multiple that number by two (2);
- Round the resulting number down to the nearest whole number;
- Subtract one (1) from that rounded number.
- This final number is the number of parts of water that you need to mix with one (1) part of your bleach to yield the diluted solution you need for decontaminating items.
When you use bleach on metal tools (alcohol is really a better option for treating metal items), be sure to rinse tools thoroughly with water after treating (to remove bleach residues) and then oil them. Bleach corrodes metal and will cause metal tools to rust if not used properly. Also use bleach carefully to prevent contact with your skin and clothing. Bleach can cause skin irritation/burns and eat holes in your clothes, if not used properly.
Now go forth and decontaminate!
For more information on plant diseases and their management, check out the UW Plant Disease Diagnostics Clinic website (https://pddc.wisc.edu/) or contact PDDC staff at email@example.com or (608) 262-2863.