Orange (fruit)
Diseases

Citrus greening disease, caused by the bacterium Liberobacter asiaticum, has been the most serious threat to orange production since 2010. It is characterized by streaks of different shades on the leaves, and deformed, poorly colored, unsavory fruit. In areas where the disease is endemic, citrus trees live for only five to eight years and never bear fruit suitable for consumption. In the western hemisphere, the disease was discovered in Florida in 1998, where it has attacked nearly all the trees ever since. It was reported in Brazil by Fundecitrus Brasil in 2004. As from 2009, 0.87% of the trees in Brazil's main orange growing areas (São Paulo and Minas Gerais) showed symptoms of greening, an increase of 49% over 2008. The disease is spread primarily by psyllid plant lice such as the Asian citrus psyllid (Diaphorina citri Kuwayama), an efficient vector of the bacterium. Foliar insecticides reduce psyllid populations for a short time, but also suppress beneficial predatory ladybird beetles. Soil application of aldicarb provided limited control of Asian citrus psyllid, while drenches of imidacloprid to young trees were effective for two months or more. Management of citrus greening disease requires an integrated approach that includes use of clean stock, elimination of inoculum via voluntary and regulatory means, use of pesticides to control psyllid vectors in the citrus crop, and biological control of the vectors in non-crop reservoirs.

Greasy spot, a fungal disease caused by the ascomycete Mycosphaerella citri, produces leaf spots and premature defoliation, thus reducing the tree's vigour and yield. Ascospores of M. citri are generated in pseudothecia in decomposing fallen leaves.
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