Biocontrol Battle Begins Against Giant Reed (Arundo)
Biocontrol Battle Begins Against
Giant Reed (Arundo)
In northern California, technician Greg Ksander (left) and
ecologist David Spencer collect a leaf sample from giant reed (Arundo
In the Southwest, an exotic and invasive weed of riparian
habitats and irrigation canals has become an absolute monster.
In its native Spain, Arundo donax, or giant reed,
is kept under control by a host of insects. But that’s not the case
here in the United States, where the invader competes for scarce water
resources, thereby harming native plants and hindering farmers’ ability
to produce crops.
“Whole riparian forests have been displaced by
Arundo, and you rarely see birds or any wildlife in these dense
patches of the weed,” says John Goolsby, an entomologist at the
Service’s Beneficial Insects Research Unit (BIRU) in Weslaco, Texas.
“The most devastating impacts of Arundo are
along the Rio Grande in Texas,” says Goolsby, who’s spearheading
ARS’s efforts to manage the weed. But Arundo’s effects are
also felt south of the border, where the reed has led to the extinction of a
rare fish species near Monterrey, Mexico.
The Weslaco laboratory is located at the heart of the
Arundo problem. But it also is the epicenter of hope for a solution.
Aerial view of Arundo near Big Bend National Park,
A Fantastic Foursome
After making multiple trips to Spain to work with scientists
there, and after testing various insects to see if they’re host-specific,
Goolsby and colleagues have identified four very promising biological controls
that could curb the impact of the destructive reed.
The candidate insects would complement existing control
methods, such as cutting the cane and applying herbicide.
Each of the four attacks the reed at a different place. A scale
insect, Rhizaspidiotus donacis, which may be released this summer,
attacks the root. The Tetramesa romana wasp attacks the main stem.
This weakens the plant, lessens its overall height, and causes it to form galls
and put out side shoots. The Arundo fly (Cryptonevra
spp.) eats the inside of new shoots, while the leaf sheath miner,
Lasioptera donacis, destroys leaves.
A Tetramesa romana larva (bottom) chews its way
through this cross section of an Arundo stem.
The wasp—which is harmless to humans—was released
earlier this year.
But the scale insect is the biological control that shows the
most promise. It feeds on the part of the plant known as the
“rhizome,” where most of the plant biomass originates. Debilitating
the rhizome could have a big impact on the plant’s growth and spread.
Another benefit: an adult female scale can produce 100 to 200
young. “This outstanding reproductive capacity demonstrates the
insect’s potential to establish large and long-lived populations on giant
reed,” Goolsby says.
The work builds upon research done earlier by former ARS
European Biological Control Laboratory scientists Alan Kirk and Rouhollah
Sobhian and by Ray Carruthers of the ARS Exotic and Invasive Weeds Research
Helping out with Goolsby’s efforts at Weslaco is
entomologist Patrick Moran, who has documented the traits, or biologies, of the
candidate agents. This information is combined with the host-specificity
data—research that Goolsby conducted—to form the basis for
petitioning USDA’s Animal and Plant Health Inspection Service for permits
to release these biological control agents.
“It’s a monumental project for our research
unit,” says John Adamczyk, research leader for BIRU. “But this is a
sustainable approach that will spread and exist in the environment for many
years to come.”
Arundo: Observations From 16
Aerial view of Arundo near Eagle Pass, Texas, along
the Rio Grande. (D1481-2)
During the past several years, ARS ecologist David
Spencer’s trips around the nation to study Arundo have taken him
to nearly every state that the plant has invaded. From a carefully tended
Arundo plant growing in the pleasant front yard of an Arkansas home,
to dense stands alongside a dirt irrigation ditch in New Mexico, Spencer has
studied Arundo’s adaptability to an impressive array of
ecosystems. His survey is likely the most comprehensive of its kind for this
weed in this country.
Spencer is with the ARS Exotic and Invasive Weeds Research Unit
in Davis, California. His ventures included collecting soil samples for
analysis by teammate Robert Blank, with the unit’s Reno, Nevada,
contingent, and collecting leaf specimens for DNA analysis by coinvestigator
Marie Jasieniuk, with the University of California-Davis.
Blank’s analyses of the types of soils Arundo
grows on might reveal whether some are less favorable for the plant than
others. Blank expects to have results later this year.
Meanwhile, Jasieniuk’s assays of Arundo’s
leaves strongly suggest that, in America, the reed doesn’t have much
genetic diversity. Subsequent studies by Jim Manhart, Alan Pepper, and Daniel
Tarin at Texas A&M University-College Station, in collaboration with ARS,
confirmed this finding and more precisely pinpointed the geographic origins of
U.S. Arundo populations.
Arundo’s low level of diversity is bad news for
the plant, but good news for those who want to stop its spread. “Plants
with a relatively narrow genetic base are thought to be less able to adapt
quickly to unfavorable environmental changes,” says Spencer.
In this instance, those changes could include attack by any one
of the four biocontrol agents—the wasp, scale, fly, or leaf sheath miner.
The ARS-university studies are the first to examine
Arundo’s genetic diversity in such detail.
This short clip shows a virtual growth model
of the invasive weed species Arundo donax, constructed using L-systems
modeling. Courtesy of ARS Exotic & Invasive Weeds Research Unit.
Also a first of a kind: the “virtual
Arundo” plant that Spencer has created. In this realistic,
computerized animation, an Arundo plant emerges from a thick rhizome
and grows on the computer screen to about 30 feet in height.
This simulation is based on a growth model, developed from
thousands of measurements of dozens of Arundo plants growing in
experiments at Davis and in natural settings. The measurements, taken with a
magnetic sensor, are processed using two different software programs.
The virtual plant can be the basis of virtual experiments in
which changes in the plant’s environment can be simulated, studied, and
used to predict the possible outcome of real-world Arundo experiments.
The on-screen plant could be used, for example, to estimate how
much water Arundo plants guzzle, based on the size and quantity of the
virtual Arundo’s leaves. Accurate measurements of the
weed’s thirst indicate how much water might—if Arundo were
brought under control—be freed up for cottonwoods, willows, and other
native plants, as well as for fish and wildlife, farms, homes, offices, and
factories downstream. Those estimates can be used, in turn, to calculate the
cost-effectiveness of Arundo control projects.
Much remains to be learned about Arundo. But the
animated Arundo plant, the DNA analyses, the soil studies, and the
biocontrol investigations are unlocking some of the plant’s secrets,
giving scientists and streamkeepers alike new knowledge that they can use to
stop the advance of this aggressive invader.—By Alfredo
Wood, Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine, an
ARS national program (#304) described on the World Wide Web at
To reach the scientists mentioned in this article, contact
Alfredo Flores, USDA-ARS
Information Staff, 5601
Sunnyside Ave., Beltsville, MD 20705-5129; phone (301) 504-1627, fax (301)
"Biocontrol Battle Begins Against Giant Reed
(Arundo)" was published in the
issue of Agricultural Research magazine.