Southeast Texas wouldn’t be the same without its tall pines. The mighty oak stands proud across the Hill Country and can be found far and wide across Central Texas and other parts of the state. But in the Rio Grande Valley and up the long coastline of Texas the palm rules, a reminder that parts of the state cross the invisible sub tropic longitude where these swaying palms dance constantly to the trade winds of the warm, salty Gulf.
But many types of palms in Texas may be in trouble now thanks to the introduction of the South American palm weevil (Rhynchophorus palmarum) in the Valley. First detected in May, the insect is a risky pest that has the potential to decimate oil and coconut palms in the Valley and others parts of the state where palms are found.
“We have been watching for the arrival of two potentially dangerous weevils to South Texas, the South American weevil and the red palm, or Asian, weevil. Using some 40 traps spread from South Padre Island to the Upper Valley, we discovered two South American weevils about a mile apart near Alamo in the early summer months,” reports Dr. Raul Villanueva, an entomologist at the Texas A&M AgriLife Research and Extension Center at Weslaco.
Of the two weevil varieties, Villanueva says the South American palm weevil (SAPW) presents the greatest problem because it can deliver two methods of destruction.
“Starting at the crown of a palm tree, the weevil will eat its way to the trunk, laying eggs along the way. As these eggs hatch, more weevils eat the tree from the inside, and worse, the South American weevil is known to carry a nematode (Radinaphelenchus cocophilus) that will deliver a deadly fungus to the palm. At this point there is no cure, the tree will die,” he said.
Villanueva says spraying the trees with specific insecticides will work, but it is costly, and by the time the first signs of damage are visible, it is too late for a chemical solution.
While the presence of the South American weevil in South Texas is cause for alarm, the entomologist says so far only the two weevils have been detected.
“Shortly after we discovered these weevils earlier this year, USDA dispatched a team of about 20 entomologists and technicians who established a much larger network of traps across the Valley, and after 4 to 5 months of comprehensive collection, no other weevils have been found. This is encouraging,” he added.
Several palms threatened
Trees that the South American palm weevil threatens include date palms, Canary Island date palms, coconut palms, African oil palms, sago palms and Washingtonia fan palms.
Villanueva says it is impossible to know how the weevils made their way into the Valley, but he speculates that a palm nursery near where the two weevils were discovered may be the source.
“This nursery imports palm fronds from South and Central America to use in floral arrangements, and the weevils may have come in on one of these fronds. It is also possible that with the large number of trucks carrying freight across the Texas/Mexico border every day the weevils were hitchhikers that made their way across the river,” he said.
The South American weevil is black and ranges in size from 1 to 2 inches in length. Sometimes the weevil will have a velvety appearance. Weevils smaller than 1½ inches are not considered a serious danger. Last year they found their way into Southern California, where the red weevil (Asian weevil) was also found.
Officials said it is difficult to detect weevil infestations because they live inside palms, but that infested palms will often suffer from notched new fronds or damage to the top of the crown.
Villanueva says the SAPW causes economic damage during the larval stage, when larvae feed on the growing tissues in the crown of the palm, often destroying the apical growth area and subsequently causing death of the palm. Populations of only 30 larvae have been reported as sufficient to cause the death of an adult coconut palm.
The red ring nematode, delivered into the palm by SAPW,releases a fungus which can kill palm trees within five months of inoculation.
While palm trees are the major target of the SAPW, the weevils will also feed on decaying oranges, which poses little threat to the Valley’s citrus industry, but Villanueva warns of greater concern as the weevil has also been known to infest sugarcane fields. If an infestation of SAPW were to occur, the Valley sugarcane industry could be at risk.
Officials warn nurseries and consumers to refrain from bringing palm trees, palm plants and fronds into the Valley and the state.
“This is the number one concern when it comes to introducing unwanted pests and diseases into an area,” Villanueva said.