Environmental Protection

Giant Weed Creates Threat to Our Nation's Ecosystems and Border Security

Weed control has become a matter of national security. Along U.S. southern coastal rivers, most particularly Texas’ Rio Grande, an invasive species of plant known as giant reed is encroaching on the water, overrunning international border access roads, and creating a dense cover for illegal activities. The U.S. Department of Homeland Security has called for a plan to control this weed.

The current issue of the journal Invasive Plant Science and Management reports on the use of aerial photography to identify areas of giant reed (Arundo donax) infestations along the Rio Grande. The study provides the first accurate estimates of these infestations and will prove useful not only to government agencies but also to land owners. It will allow the estimation of water usage and economic losses, and help devise a plan for management of this invasive species.

Giant reed, more commonly known as Carrizo cane in Texas, is a nonnative bamboo-like plant that can grow more than 32 feet tall. To support its rapid growth rate, it consumes large amounts of water compared to native vegetation. The weed reduces arthropod diversity and abundance in our ecosystems and destroys wildlife habitat.

This vegetation threatening our watersheds also has stems and leaves containing several toxic or unpalatable chemicals, which can discourage native insects and other grazers from helping to reduce its numbers. It is, however, a good candidate for biological control methods. The eurytomid wasp has been tested in a small area of release and found to be a specific enemy to the giant reed, and unlikely to harm native plants.

Aerial photography has provided the first step in the battle against this green giant. Identifying areas of infestation to target in wide and inaccessible regions of Texas along the Rio Grande can be a difficult task. Remote sensing, provided by aerial photography, has enabled the differentiation of giant reed from other vegetation because of its light reflectance characteristics.

Mapping the spatial extent of giant reed infestations provided necessary information to gain approval for the release of biological control agents, such as the wasp. Aerial photography offers a relatively inexpensive method to perform this mapping and gives finer resolution than satellite digital imagery.

Full text of the article, “Mapping Giant Reed (Arundo donax) Infestations along the Texas–Mexico Portion of the Rio Grande with Aerial Photography ,” Invasive Plant Science and Management, Vol. 4, No. 4, October-December 2011, is available at http://www.wssajournals.org/

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