Exocortis—
Citrus exocortis viroid
Exocortis disease is generally of minor importance in California because regulations on budwood sources keep new plantings largely free of this and other known viroid diseases.
Identification
Dry, cracked bark that lifts in strips and may peel off the root crown (bark shelling) is the characteristic symptom of exocortis. Droplets of gum commonly appear under the loose bark.
Life cycle
Citrus exocortis viroid is easily spread in infected budwood and on contaminated propagation and pruning tools. When a tree is infected, bark shelling sometimes develops slowly for several years, and diseased tissue is restricted to a small area. In other instances the disease develops rapidly over the entire rootstock.
Damage
The growth of trees infected with Citrus exocortis viroid is slowed and fruit yield declines gradually over the years. But trees are rarely killed by the pathogen. Exocortis disease develops only in certain susceptible rootstocks, most commonly trifoliate orange and its hybrids. Rangpur lime and some citron and lemon rootstocks are also affected. The disease is generally seen only in old citrus trees because current propagation methods generally prevent infection in citrus nursery stock.
Solutions
It is best to remove infected trees because pruning clippers and saws can transmit exocortis to other citrus trees unless the tools are thoroughly cleaned and disinfected after working on an infected tree. Replace infected trees with those that are certified as free of known viroids, such as those from the University of California's Citrus Clonal Protection Program.
After using propagation and pruning tools on a tree with exocortis, before working on another citrus tree, scrub or wipe the tools clean. Then disinfectant dip or spray them with a 10 to 20% bleach solution, 70% ethyl alcohol, or a commercial disinfectant that is allowed to remain in contact with the tools for several minutes.
Adapted from Integrated Pest Management for Citrus and Pest Management Guidelines: Citrus, University of California Statewide Integrated Pest Management Program (UC IPM). |
