Brazil’s Fundecitrus is alerting citrus growers to take extra measures against leprosis during the current critical period for disease occurrence, May to September. At this time, fruit are in development, and the lack of rain favors outbreaks of the leprosis-transmitting mite.
Leprosis is an important disease of Brazilian citrus that in recent years has caused significant damage to orange groves. It has the potential to cause intense and premature fruit drop, defoliation and drying of branches. It drastically reduces the production and longevity of trees.
Sweet oranges are the most susceptible variety to leprosis. Some citrus types, such as Tahiti lime and Murcott tangor, are resistant to the leprosis virus.
In Brazil’s last harvest, leprosis was the fifth most responsible cause of premature drop in oranges, causing an estimated loss of 7.94 million boxes.
The disease is found in all Brazilian citrus-producing regions. In São Paulo, it occurs throughout the state, with greater intensity in the north and northwest.
One of the main management strategies is the application of acaricides to keep the mite that transmits leprosis at low levels. Fundecitrus researcher Renato Bassanezi said there are few efficient acaricides available in citriculture for the leprosis mite. The recommendation is not to make sequential applications of the same product.
“It is essential that citrus growers take extra precautions during this period,” Bassanezi said. “To avoid selection of resistant populations, one of the strategies is not to repeat the same active ingredient and rotate acaricides with different modes of action. With this, it is possible to preserve the efficiency of the few products available on the market.”
Bassanezi said the best results in controlling leprosis mites occur when infestation in the orchard is still low — when less than 3% of the fruit have the mite present. “The citrus grower must monitor at least 2% of the plants, observing three to five fruits per plant, at most every two weeks,” the researcher advised.
To detect increased pest populations, monitoring should be conducted by professionals trained in the identification of the leprosis mite.
Other management strategies should be used to lower the mite population, such as eliminating weed hosts for the mite and removing all fruit at harvest, leaving no fruit remaining on the tree.
The leprosis mite moves short distances but can also be dispersed by being carried on crop material, infested plants and fruits, and by wind. Therefore, growers should plant healthy seedlings free of the mite, clean the harvesting equipment to avoid introducing the mite into areas free of the disease, and harvest healthy plots before harvesting the plots with a history of infestation.
Periodic pruning of branches with leprosis lesions helps to reduce the source of virus within the orchard, in addition to restoring the health of the plants.
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