> if you have citrus in your yard > please be very vigilant in checking > your trees for [the citrus psyllid > vector of citrus greening.] DO NOT > transport citrus > into or out of your area. Most here won't know what this is. Citrus greening is a disease caused by a bacterium lacking a cell wall. For this reason the bacterium does not tolerate drying and can only be spread wet. It infects the fluid transport system of plants in family Rutaceae. This includes citrus, white sapote (Casimiroa edulis), the herb rue (Ruta graveolens), and tropical shrubs commonly called mock oranges (Murraya paniculata), though not the temperate "mock orange" which is genus Philadelphus. Similar bacteria cause human disease, known in English as "walking pneumonia" but citrus greening does not infect humans. The disease and its vector, the aforementioned psyllid, are native to eastern Asia. The psyllid feeds on most members of Rutaceae and transmits the bacterium on its proboscis. This is the reason Rutaceae have been on the USA no-import list for some years. A psyllid in English is colloquially known as a leafhopper (which is different from and smaller than a grasshopper.) The greening psyllid is so small, and so similar to other psyllids, that it cannot be identified without a microscope. Many county agriculture departments provide study traps to commercial and home orchardists with citrus trees. Genetic analysis shows the psyllid was brought to the New World in the 1500s or 1600s, probably with cultivated citrus or Murraya shrubs. The disease arrived much later; South America some time ago, and Miami, Florida in the 1990s. The disease in the USA is genetically distinct from that in Brazil, and is more closely related to strains in China; for this reason, it is thought it was introduced to Miami from China. Vector and disease quickly spread through citrus groves throughout Florida despite herculean and sometimes shockingly, lethally violent government attempts to control it. It arrived in Los Angeles in the early 2000s and continues spreading. Citrus greening kills citrus trees. There is now no successful treatment for infected trees. Trees are infected for 3-4 years before showing signs, and psyllids feeding on infected but asymptomatic trees can spread the disease to other trees. Seeds may bear the disease because most citrus have polyembryonic seeds, formed by parthenogenesis. Symptoms are those of inadequate fluid transport: Stunted growth, and fruit which falls off the tree with any water stress. Almost all fruits are affected. They bear skin scars and are bitter. It is predicted that if a control method is not found, the citrus industry in Florida will disapper soon. As of now the only method of control is prevention of spread of the vector. USDA citrus germplasm repositories now house collections in containers in triple-screened greenhouses to prevent entrance of the psyllid. The bacterium is quite susceptible to antibiotics but there is no effective way to disperse antibiotics through tree vascular tissues. Study of insects possibly parasitic on the psyllid are underway. Current thinking is that the US citrus industry will only be saved by genetically engineering citrus to be resistant to the bacterium. There has been some research showing the common guava (Psidium littorale) repels the psyllid, and some growers are interplanting citrus orchards with guava. Recommendations are also to remove members of Rutaceae from landscapes at risk, and not to plant other plants in this family. Arizona is the last state in the US that can grow organic citrus without pesticides. Those of us active in fruit gardening clubs in Arizona have been following this issue for some time. The psyllid is in the citrus fields just across the Colorado River from Arizona near Blythe and Yuma, as well as Hermosillo, Sonora, Mexico, just a few hundred miles south. The intervening desert has so far prevented spread into metro Phoenix but summer storms could bring the psyllid, the way hurricanes brought certain kinds of soybean rust from the Yucutan Peninsula to the US midwest some years ago. Some of us are currently interplanting or preparing to interplant our orchards with guava. Leo Martin Phoenix Arizona USA