Palm tree-killing weevil found in South Texas

October 23, 2012 by Rod Santa Ana
The South American palm weevil is black, about an inch and a half long and causes severe damage to many species of palm trees. Credit: AgriLife Extension photo by Dr. Raul Villanueva

An intensive, area-wide survey of the Lower Rio Grande Valley has detected the presence of a palm tree-killing weevil that has caused extensive damage in other parts of the world, according to Dr. Raul Villanueva, an entomologist at the Texas A&M AgriLife Research and Extension Center at Weslaco.

"For the past year, we've been on the lookout for two invasive species of weevils that have caused great damage to in the tropics of the world," he said.

"Unfortunately, in April and May we found the South American at two locations in Alamo. The good news is that there's no sign yet of the Asian, or red palm weevil."

The South American palm weevil is black, about an inch and a half long and originated in Central and South America, he said. It then spread to Mexico and California where it has killed many oil and coconut palm trees.

The South American palm weevil is especially wretched because it can kill palms with a one-two punch, Villanueva said. Not only does it weaken a tree by eating its insides, it is also a vector of a nematode that transmits a deadly fungus.

"These weevils get into the crown of a palm tree and moves into the trunk, all the while consuming internal tissue and laying eggs as they go," he said. "Those eggs hatch and also burrow into the trunk. Weakened trees can die from a lack of leaves or from secondary infections.

Dr. Raul Villanueva, an entomologist at the Texas A&M AgriLife Research and Extension Center at Weslaco, checks a trap similar to the one that captured a South American palm weevil in Alamo. Credit: AgriLife Communications photo by Rod Santa Ana

"As if that weren't bad enough, this weevil can also carry a nematode, a tiny worm, that promotes a fungus in coconut palm trees called red ring disease. Like the weevil, the fungus attacks young shoots of the tree."

Damage to leaves is especially threatening to palms because unlike a tree with many shoots, or branches, palms have only one, he said. If that shoot is severely damaged, new leaves, or fronds, won't emerge which kills a palm tree.

"There's no way to determine how this weevil got here," Villanueva said. "It could have come in as a hitchhiker on an imported palm or ornamental plant. That's why it's so important to not bring plants, especially palms, citrus trees and ornamentals, into the Valley from outside the area. They can carry insects and diseases that are very harmful to our crops and landscaping."

There is no cure or treatment for trees infested with the South American palm weevil, Villanueva said.

"There's a systemic insecticide that can be used, but it's very expensive and by the time a person notices the weevil, it's too late; the damage has been done," he said.

The South American palm weevil affects several species of palm trees used extensively in South Texas landscaping, including coconut palms, date palms, Canary Island date, African oil palm, sago and Washingtonia fan palms, Villanueva said.

"In addition, this weevil can feed on sugarcane, and adults can feed on ripe fruits without really causing significant economic damage. Fruits would include citrus, guava and papaya."

Because the South American palm weevil is not native to the area, there are no natural enemies to keep their populations in check, Villanueva said. That, plus the fact that there is no efficient insecticide, means that this insect could cause major headaches for horticultural interests.

"This invasive species can threaten the ornamental palm industry, not only in Texas, but throughout the South," he said. "Especially hard hit may be those nurseries that produce palm trees for interior landscapes like malls, both locally and farther north. A large palm tree can cost $3,000 to $4,000. Preventive spraying of insecticides may reduce weevil populations, but they will be costly."

Villanueva said that without natural enemies to control populations, the weevil could affect the South Texas sugarcane industry, but doubts it will be a problem for the citrus industry.

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