Psorosis

Infected trees, mostly orange and grapefruit, slowly decline; main scaffold branches die and trees become unproductive. The most distinguishing field symptom is scaling and flaking of the bark on the scion. Symptoms, including interveinal yellow flecking on young leaves, may appear in fall. During early stages, patches of bark on the trunk or scaffold branches show small pimples or bubbles, which later enlarge and break up into loose scales. Gumming often appears around the margins of a lesion. In advanced stages, deep layers of bark and the wood become impregnated with gum and die.

Psorosis is a graft transmissible disease, caused by a virus, most often found in old citrus plantings. It is transmitted in infected budwood or possibly with contaminated grafting tools. Occasionally, the disease spreads through root grafting from an infected to a healthy tree. Seeds of some citrange cultivars are known carriers of the disease.

As with other graft transmissible diseases, the use of disease-free budwood is the major method for preventing damage from psorosis. The Citrus Clonal Protection Program provides budwood free of major diseases to nurseries and growers. Where an old tree shows symptoms, scrape away the infected bark area to stimulate the formation of wound callus, which results in temporary recovery. Generally, a psorosis-infected tree will be less productive than healthy trees, and replacement is the best option.