Research has shown that exocortis and cachexia viroids can frequently be spread from infected plants to healthy plants on clippers, budding knives and other tools used in pruning and budding. Viroids can cause stunting and back scaling on susceptible rootstock or certain scion combinations.
Exocortis is a disease affecting certain rootstocks such as Poncirus trifoliata; many citranges, including Carrizo and Troyer; some citrumelos; Rangpur lime; and sweet lime. Cachexia is a disease primarily affecting some mandarin types, and rootstocks such as Rangpur lime and sweet lime.
To minimize the mechanical spread of these disease-causing organisms between budwood source trees, a solution of household bleach (1.05 sodium hypochlorite, final concentration), 20% by volume, in water, can be effectively used to sterilize tools. Household bleach is usually around 5.25% sodium hypochlorite. This is very caustic, even at a 20% by volume dilution. Use caution when mixing and handling.
Bleach rapidly loses its strength in the heat and sun. Fresh solutions should be prepared daily. Dip clippers, knives or pruning tools in the bleach solution for a few seconds. Tools can be stored or coated in spray oil or washed after use and then stored dry to prevent rusting.
Alcohol, flame and other bacterial disinfectants are not effective sterilants for exocortis viroid. Clippers need to be sterilized between each tree when cutting budwood, and budding knives and pruning tools need to be sterilized in the nursery.
Add 200 milliliters of household bleach to 800 milliliters of water. Or add one part household bleach to four parts water. For example: 1 cup household bleach and 4 cups water.