Giant Cane Invasion
Researchers and economists investigate biological controls
By Danielle Supercinski
Researchers are investigating biological controls for giant cane (Arundo donax), a non-native invasive weed, which has formed dense thickets lining Lower Rio Grande Basin waterways, exhibiting a fast growth rate and consuming large quantities of already limited water supplies.
“Giant cane presents a severe threat to agro-ecosystems and riparian areas where it chokes river sides and irrigation channels, consumes excessive amounts of water, displaces native plants and reduces wildlife habitat,” said Dr. John Goolsby, research entomologist with the U.S. Department of Agriculture–Agricultural Research Service (USDA–ARS) at Weslaco.
“In addition, giant cane serves as a protective cover to those that would enter the United States illegally, including potentially those who would harm the country,” said Dr. Ron Lacewell, economist with the Texas A&M University (TAMU) Department of Agricultural Economics.
Giant cane can thrive in dry ditches and flooded drainages with varying water resource availability. Despite its proximity to water resources, direct estimates of giant cane water consumption are lacking.
“There is a strong need to quantify transpiration in this species and to better understand how stresses such as herbivory and drought alters water consumption,” said Dr. Georgianne Moore, assistant professor in the TAMU Department of Ecosystem Science and Management.
A team of scientists and specialists are conducting giant cane work in the Rio Grande Valley with various collaborative ties.
Moore’s research focuses on conserving water through biological control of giant cane in the Lower Rio Grande Valley as a component of the Efficient Irrigation Rio Grande Basin Initiative (RGBI) project. During 2006-2007, year one of the RGBI giant cane project, researchers reared prospective biological agents for giant cane, and graduate student David Watts began work to estimate daily water loss per unit area in infested plants. In addition, he is measuring transpiration rates of existing giant cane stands within the riparian area of the Rio Grande Basin to determine the amount of water used. In the future, successful use of biological control may lessen the impact giant cane has on the landscape, both in terms of reduced competition with native plants and reduced water consumption.
Other researchers and specialists are also focusing on the problems giant cane is causing for the basin. Goolsby and his research team are researching three beneficial insects – Tetramesa romana (wasp), Cryptonevra (fly) and Rhizaspidiotus donacis (root scale) – for potential biological control of the plant.
“Three prospective agents collected from Europe are being reared in quarantine facilities in Texas,” Moore said. “Rhizomes from giant cane have been collected in the Lower Rio Grande Valley and are being propagated in pots for greenhouse experiments.”
Moore said insect agents successfully fed on potted giant cane in the initial trials. Sufficient-sized colonies of the wasp in particular have been gathered to conduct greenhouse experiments, which began in spring 2007.
“The focus of year two of this project will be to expand current greenhouse and field studies to investigate the interactions between herbivory and drought,” Moore said. “We will also investigate temporal variability in transpiration and productivity throughout the growing season. This is an important next step toward predicting water use under the wide range of growing conditions in the Rio Grande Basin and toward finding an effective biological control agent.”
Department of Agricultural Economics personnel are conducting additional RGBI efforts on giant cane. The economists include Dr. Ron Lacewell, assistant vice chancellor for agriculture and life sciences; Dr. Ed Rister, professor and associate department head; Allen Sturdivant, Extension associate–risk management; and Emily Seawright, student technician. Texas Cooperative Extension, Texas Agricultural Experiment Station and Texas Water Resources Institute are also key collaborators in these efforts.
RGBI economists are developing growth models representing the plant’s height, density and area of spread to project future cane infestations without any control. Subsequent to the development of these models, a monetary value associated with the water loss, due to uncontrolled growth of giant cane, will be estimated.
“After the safety and efficacy of the beneficial insects have been fully researched, projections will be estimated of the reduction in giant cane growth due to the biological control,” Seawright said. “Subsequently, the net water savings with the control of giant cane will be calculated, allowing the potential value of introducing the beneficial organisms into the Rio Grande Basin to be determined.”
Economists anticipate estimating the potential lost economic activity to the Basin from the giant cane invasion, and the economic and financial benefits (dollars per acre-foot) of adding water to the agro-ecosystem through management of this exotic weed via beneficial pests.
“Giant cane’s water consumption prevents the potential use of water toward agricultural crops which produce economic activity,” Sturdivant said. “The estimated net costs and benefits of a management program, which adds water (by reducing giant cane), can be calculated and compared to other measures that add (or save) water.”
In collaboration with USDA–ARS, the economists will investigate and perform economic analyses associated with a potential management program for controlling giant cane. Currently, research on these topics is under way through RGBI, USDA–ARS and numerous other researchers with an explicit objective to save/add water to the region by reducing giant cane.
