Since they are easy and fast to grow, but above all for their majesty that evokes wealth and elegance, the palm trees of the species phoenix canariensis They are the most popular arborescent plants in landscaping and gardening on the five continents.
Coming from the Canary Islands, they came to the country through President Miguel Alemán (ruled from 1946 to 1952), who saw them on a visit to Los Angeles, California and decided to bring them to Mexico City.
Today, almost 80 years after their arrival, these plants face various diseases, pests and fungi that cause most of the specimens to perish and the rest to fall ill.
“There are several organisms that can be associated with the death of a palm tree. Among the most common are the red weevil, the false leafhopper and the moth; there may also be viruses, bacteria and fungi (that of the genus fusarium is the one that maintains the greatest presence). Several of these can lodge and attack a single specimen ”, explains in an interview the biologist Ivonne Olalde Omaña, academic technician of the Botanical Garden of the Institute of Biology of the ONE.
Divine foreigners
Palm trees are not trees: they are arborescent plants, that is, they have the shape of a tree but in reality they are not, since they do not form wood; the so-called trunk is the union of the leaves, not a true trunk.
Its growth area is concentrated in the center and at the top, which is why it is difficult to know what happens to pests because that is where they lodge.
As mentioned before, they are endemic to the Canary Islands, where they are considered a symbol. The first document that is had on the cultivation of the Canarian palm tree outside its place of origin comes from Norway. The botanist Christen Smith met her during a trip to the Canary Islands in 1815 and collected seeds that he took to the Oslo botanical garden, where many of them germinated. He was the first to introduce the phoenix canariensis in Europe. One of his palm trees, which became known as “Smith’s palm,” grew in a greenhouse until it died in 2000, at the age of 185.
Palm trees came to the United States during the so-called golden age (1878-1889), when the wealthiest entrepreneurs began building mansions and hotels in Florida that required large landscaping and gardening projects.
In those same years they were also imported to South American countries such as Ecuador, Chile, Argentina, Bolivia and Peru, where they are used as ornaments for squares and parks, as well as Asia and southern Spain.
Its journey around the world was achieved thanks to the fact that this plant adapts to any climate: from sea level to 2,500 meters of altitude. Palm trees also host and serve as a refuge for various birds and mammals. Another feature is that they can measure up to 20 meters, although the space where it is is influenced because it depends on the availability of water and nutrients.
How they get sick
Olalde Omaña details that the red weevil and the false leafhopper are insects that feed on these plants; they reach the top of the palm tree, eat there and lay their eggs.
“Worm-like larvae hatch from the eggs and begin to form galleries in the center of the palm tree. Bacteria and fungi can easily get into these tunnels. These spread through the internal tissue, make a kind of fermentation and the center of the palm tree dies, it no longer recovers because its growth zone is directly affected. There are also other organisms that can be in the soil, such as nematodes (round worms, they have elongated and cylindrical bodies), which also affect them ”, he explains.
According to the Ministry of the Environment of the capital (Sedema) in Mexico City there are records of mortality of palm trees since 2011.
Another problem, the biologist points out, is that these pests do not have a natural predator in the capital to stop them. “In their place of origin there is surely some bird or reptile that feeds on them, that’s why the population is controlled there. That food chain does exist there. But when we remove both the palm tree and the insect from their natural environment, we break that balance. Here in the city we do not have a top animal that feeds on these insects and that is why the population of pests can grow so much “.
However, he admits that the insects that may be the carriers of the viruses “are not invincible and could be controlled.” The problem is to detect them when they reach the palm tree, monitor them and prevent them from expanding, since they can have several generations in a year if the weather is good, that is, “if it is hot and there is humidity. And in Mexico City it is getting hotter and hotter ”. They can even have two or three generations: each generation can lay up to 200 eggs.
The specialist adds that the risk is that these insects, even fungi, can pass to other types of palm trees that are nearby. “They could then affect Mexican palm trees, in addition to the fact that we can lose a large part of the vegetation that is in the city; In other words, if we have many palm trees and they die, we lose that coverage; the ideal in this case would be to replace them with native plants ”.
Until July of this year, staff from the Ministry of Works and Services of the capital (Sobse) has removed 27 dry palm trees and made the opening of 64 vines for the planting of 25 palm trees of the species phoenix canariensis, which will later be replaced with palm trees washingtonia robusta.
“It would be best if no palm trees of any species were planted again, because they can be reinfected, while the fungi may still be in the soil of the palm that died; the pathogens are still there, ”he says.
native
“Nobody denies the beauty of palm trees or any other exotic plant, but they are species that often do not work for natural processes of the ecosystem where they arrive and can disrupt the natural balance of the place,” says the specialist from the Botanical Garden of La ONE.
For this reason, he recommends that in Mexico City the palm trees be replaced by endemic species such as pines, oaks or strawberry trees.
Capulines and tejocotes can also be planted in ridges and green areas. “These species are recommended because, in addition to the ecological benefits they provide, they produce fruits that can be fed to birds, mammals and even reptiles such as lizards. They all need food and these trees can provide it ”.
The idea, he adds, is that the municipalities look for these endemic species, because they are the first to carry out large plantations and reforestations. However, “currently we see that several streets of the city were remodeled and the new thing that was put on was once again exotic. They would have to propagate these native plants ”, he concludes.
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