Sunblotch not easily spread by avocados

Agricultural experts are unanimous that avocado sunblotch is spread by grafting and infected pruning tools.

This is the disease that caused Costa Rican plant health officials to cut off avocado imports last May 5.

The decision has created an international incident mainly involving México.

Plant health officials from México met with representatives of the  Servicio Fitosanitario del Estado of the Ministerio de Agricultura y Ganadería.

The plant health service put out a statement Thursday that said the action was taken because Costa Rican officials realized that the country was free of avocado sunblotch. The statement also showed that officials here realize that the causal agent of the disease can be spread also by the avocado seed.

The disease has been recognized since early in the 20th century. Recent research blames a viroid, a small piece of genetic material smaller than a virus, for the infection. These virods are also spread by pollen, but the research available online says that under such conditions only the avocado fruit and not the tree becomes infected.

It appears that in order to bring the disease into Costa Rica, someone would have to import infected trees or infected seeds. In the latter case, they would have to raise seedling from the seeds and then graft the bud or branch of the seedling onto a health tree.

The best protection against the disease, according to online sources, including Plant Health Australia, is for growers only to purchase blotch-free plants and to sterilize pruning equipment when moving from tree to tree.

Plant Health Australia also said: “Sunblotch can be transmitted on sap-contaminated pruning blades, harvesting clippers and injection equipment. It can be transmitted in pollen, but only the developing fruit, and not the fruit-bearing tree, are infected.”

Francisco Dall´Anese Alvarez is the director of the  Servicio Fitosanitario del Estado. His actions have causes some to think his decision was protectionist for the benefit of Costa Rican growers instead of protecting the trees from Méxican contamination.

The Hass avocados from México have been the staple of Costa Rican cuisine. This is the black avocado with the bumpy skin.

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