The symptoms should not be mixed up with those of citrus ringspot virus. They are visible on leaves, fruit, bark, trunk, roots and branches. Leaves exhibit a variety of symptoms, from chlorotic flecks or spots, to discoloration in the form of mottling. Symptoms may fade as leaves mature. Psorosis-infected fruits may develop ring-shaped chlorotic patterns. However, the most common symptom of the disease is the deterioration of bark. This usually starts with the appearance of blisters or bubbles which later enlarge and split open, resulting in bare patches and loose scales of bark. The flaking or scaling later extends to the rest of the trunk and main branches. 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.
The symptoms are caused by the citrus psorosis virus, which is considered to be one of the most detrimental virus pathogens of citrus trees worldwide. It is mainly transmitted through infected budwoods or contaminated tools during grafting. Occasionally, the disease spreads through natural root grafting from an infected to a healthy tree. Seeds of some citrange varieties are known to carry the disease. There is also some evidence of natural spread, possibly by the fungus Olpidium brassicae, or by a yet unknown aerial vector. The incidence of psorosis has been reduced in many areas by using budwood certification programs. Mainly orange and grapefuit are affected but mandarin, tangerine, lemon, pomelo and lime may also develop symptoms.
To this day there is no known biological control treatment to reduce the incidence or severity of this disease. Please notify us, if you know of any.
Always consider an integrated approach with preventive measures and biological treatments if available. Virus diseases can not be directly controlled by usage of chemical treatments. When psorosis is present in a grove, disinfection of tools should be practiced by dipping pruning or budding tools in a solution of bleach. The best way to prevent the disease is to acquire certified, disease-free budwoods for grafting.