Left: A gardener in Parco Bonaria explains how the red palm beetle works, drilling into the heart of the palm. Center: Lots of treatment marks on this palm. Right: The beetle behind the palm deaths: Rhynchophorus ferrugineus.
While in Cagliari, kept seeing circular paint marks on palm tree trunks and we would mutter to ourselves something like: “those damn graffitists, marking up a tree, really!?”. The mystery didn’t reveal itself until our 6th day when we stopped to talk to a gardener in the Parco di Bonaria.
What first caught our attention were orange buckets hanging in trees. It was just too tempting and when we saw a gardener sitting there, we decided it was time for an explanation and a language lesson. (We find that people – be it a docent in a museum or a gardener in a park – just love to talk and it’s a great way to practice Italian.) Well, this gardener helped crack the mystery so much so that our visit to the nearby santuario was a bit of letdown. (In this instances, facts trump faith.)
The marks on the trees, concentric circles of yellow, red, blue, and green are a way to keep track of which trees have been treated for the red palm weevil, Rhynchophorus ferrugineus. Each circle represents an intervention, or use of insecticide. The infestation of this beetle from Asian has been devastating to palm trees around the Mediterranean. It mostly targets the Phoenix canariensis pictured here, although it’s not just limited to this host. I remember first becoming aware of the seriousness of the infestation when we were in Seville, Spain two years ago (see A tour of Andalusia: Córdoba, Seville and Granada) and we saw many palm stumps, trees with no tops. The beetle kills the tree because the larvae burrow into the heart of the palm weakening and eventually killing the host by eating its heart out.
Cagliari seems to have a marking system with lots of variation. We saw big and small circles. Even the gardener lamented the fact that everyone does it differently. You would think they would have adopted a system a little more aesthetically pleasing to look at like smaller, uniform circles or metal tags that can be punched. Why didn't they ask us first?
Oh, the bucket hanging from the tree, that was filled with pheromones and soapy water. The beetles are attracted to the sex-in-the-bucket and get covered with soapy water, which cuts off how they breathe, and they die.
Treated and dead palms (note stumps) in the Gardini Publici in front of the Galleria Comunale d'Arte Moderna, Cagliari.
Left: Parco Bonaria marked palm. Center: An orange bucket filled with pheromones. Right: A palm in Parco Bonaria already sick, note yellowing fronds.