Carrizo Cane – Another Mexican Border Problem
Arundo cane starts in moist areas, usually around bodies of water, and then moves inland.
By Robert Fears
U.S. Border Patrol and other law enforcement agencies have a tough job attempting to stem the constant flow of illegal immigrants and goods across the Rio Grande River. One of their difficulties is created by Carrizo cane, which hides the river from view and prohibits access.
Carrizo cane has many synonyms including arundo, phragmites, giant reed, arundo grass, elephant grass, Spanish cane, wild cane, donax and oboe grass.
The plant’s scientific name is Arundo donax, from which the common names arundo and donax are derived. The plant is most often referred to as Arundo cane or giant reed. The plant is a bamboo-like grass with stems comprised of hollow internodes and solid nodes. From a distance, it looks like a corn plant.
According to USDA Forest Service, Carrizo cane is an Asian native and was cultivated for thousands of years in southern Europe, northern Africa and the Middle East. It was introduced into southern California as an ornamental and was used as an erosion control species along drainage ditches. Now the state has several programs in place to eradicate the cane.
“Arundo cane causes major problems for the Border Patrol because of its height and density,” said Bryan Gentsch, Ph.D., managing director of Association Strategies. Gentsch is a weed scientist who is advising government agencies on how to deal with the cane.
“During summer, Carrizo cane can grow as much as a foot per day reaching a height of 25 feet or more. Given sufficient sunlight and water, the cane can transform from a sprout to a 25-foot plant within a month,” Gentsch explains. “A density of 10 stems per square foot is not uncommon, making it virtually impenetrable without the use of a machete or other cutting device. Smugglers cut paths through the cane which allow them to travel as a much as 1 mile across Texas landscape undetected under dense cane foliage,” he says.
Carrizo cane causes other problems
Carrizo cane is a water-loving plant found along stream banks, desert springs, floodplains, drainages and irrigation waterways. It can establish in most moist soils regardless of the location, and occurs with saltcedar and Russian olive in many southwestern riparian areas. Establishment, however, is usually limited to locations lower than 5,000 feet elevation. The plant grows prolifically around lakes and along streams in Austin. It is rapidly moving inland from the Rio Grande, rendering thousands of acres of privately owned rangeland useless for livestock and wildlife.
The robust plant cannot be grazed because of plant density. It has limited palatability to ruminants due to its high fiber content. Cattle will eat younger plants, 20 to 40 inches high and the tips of older shoots when they can reach them.
It is inaccessible to wildlife for food or habitat. The plants are unsuitable for aquatic and upland birds except for roost sites of the white-collared seedeaters. Habitat for these tiny finches is weedy places, tallgrass, and brush found mainly in weedy overgrown fields or brushy open woods, typically close to water.
“Unlike native riparian plants, giant reeds provide little shading to the in-stream habitat,” reports California Invasive Plant Council (CIPC). “Lack of shading leads to increased water temperatures and reduced habitat quality for aquatic wildlife.”
Carrizo cane is suspected of reducing groundwater availability by its intake of large amounts of water. The Forest Service reported that one study showed that the cane can transpire 56,200 acre-feet of water over the course of a year, as compared to 18,700 by native vegetation.
“Arundo cane alters channel structure by retaining sediment and constricting water flow,” reports CIPC. “Although once planted for erosion control, the giant reed can promote bank erosion because its shallow root system is easily undercut and bank collapse may follow. Uprooted plants, due to erosion and flooding, pose clean-up problems when deposited on banks or in downstream estuaries. During flooding, uprooted plants create hazards when trapped behind bridges and other structures.”
When dry during summer and drought, Carrizo cane is extremely flammable. Due to a large amount of biomass, it produces a very hot fire that spreads rapidly. The cane often grows near and in urban areas, which poses a serious threat.
Especially important to cattle raisers, hunters and wildlife managers, is that Arundo cane enhances survivability and reproduction of the dreaded fever tick. Blood-engorged female ticks detach from their host animals (usually cattle, deer or nilgai) and drop to the ground. They release 1,000 to 2,000 eggs before dying. Newly hatched seed ticks, or larvae, crawl up plants where they wait for a host animal to pass by.
USDA Agricultural Research Service (ARS) scientists have found that the fever tick quarantine area in South Texas is extensively overlain with dense, wide infestations of Carrizo cane, which causes more difficulty in controlling the pest. Overhead canopies of cane reduce soil temperature, which creates a suitable environment for an increased number of female ticks laying larger egg masses, compared to open grassland or native brush where soil temperature is higher. It was also learned that Arundo harbors less ground-dwelling predators of fever ticks, such as spiders and ants.
What actions are in place to control Carrizo cane?
On June 3, 2015, Governor Greg Abbott signed into law Texas Senate Bill 1734, probably the shortest legislation ever written. The bill simply states, “The state board shall develop and implement a program to eradicate Carrizo cane along the Rio Grande River.”
“The state board” refers to Texas State Soil and Water Conservation Board (TSSWCB). Senate Bill 1734 was introduced by Senator Carlos Uresti, D-San Antonio, and its rapid passage through both houses of the Legislature and across the Governor’s desk signifies deep bipartisan concern over the open Texas/Mexico border.
TSSWCB immediately commenced researching methods of controlling Carrizo cane. Primary reproduction of Carrizo cane is vegetative with sprouts occurring from disturbed stems or rhizomes, some of which are buried 3 to 10 feet deep. The cane flower is a dense plume, 1 to 2 feet long, which produces many seeds.
Seed fertility is very low, however, and seedling establishment from germinated seed is quite rare. This behavior makes the plant hard to control, especially through mechanical methods. Prescribed fire as a single treatment is also not effective because it will not kill the underground rhizomes.
ARS scientists released Arundo gall wasps (Tetramesa romana) and arundo scale insects (Rhizaspidiotus donacis) in 2009 as part of a biocontrol program to kill Carrizo cane along the Rio Grande River. The research team combined “topping” — mechanically cutting cane — with insect releases. They have learned that topping suppresses growth for more than a year and makes the plants more susceptible to insect attacks.
These insects are slowly rendering adverse effects on cane over 550 river miles. Measurements taken in 2014 (5 years after release) documented a 22 percent decrease in plant biomass and in 2016 (7 years after release) an additional 28 percent decrease was shown. In summation, a 50 percent decrease in biomass has occurred during a 12-year period. These data show that the insects are very effective if allowed enough time to complete the task. The good news is there is a significant recovery of native vegetation.
A quicker way to control Carrizo cane is by an aerial application of herbicides that translocate from foliage into the deep rhizomes for complete plant kill or injury.
Two herbicides have shown to be effective on the cane — glyphosate and imazapyr. These are the names of active ingredients and each is marketed under several product names. Texas A&M AgriLife Extension Service listed glyphosate as providing good control of Carrizo cane and rated imazapyr as excellent.
After TSSWCB studied the options, secured limited funding through grants and conferred with landowners, the organization decided to treat Carrizo cane with imazapyr because of its effectiveness and the shorter time required for control.
This decision created opposition from some environmental groups and local governments, which expressed concern that imazapyr would contaminate water in the Rio Grande River. The practice has been prohibited by the Webb County Commissioner’s Court.
Imazapyr, as well as glyphosate, are labeled for use on aquatic sites. Three to 5 annual applications may be required for complete control, but treated areas opened to sunlight could allow re-establishment of native vegetation.
It is extremely hard to receive acceptance for aquatic labels from Environmental Protection Agency (EPA). Many laboratory and field tests are required for terrestrial-use labels, such as toxicity to a multitude of organisms, human exposure, residues, metabolism and behavior in soil and water. Aquatic labels require toxicity tests on additional aquatic organisms and more behavior tests in water. By the time an herbicide is placed on the market, its characteristics are well understood.
Since Carrizo cane does not grow in the water, only the riparian area is sprayed. Modern spray application technology allows herbicide mixtures to be placed directly on target. The author has stood at the edge of treatment swaths during spray application tests without getting the toes of his boots wet.
The city of Austin has successfully sprayed Arundo cane along Lady Bird Lake without any adverse effects. They cut the cane and then sprayed herbicide in 2011 as plants grew back. A second spray application was made in 2012 to areas where the cane was not completely controlled.
Funds were not appropriated for the enactment of Senate Bill 1734, but a grant was awarded for conducting a pilot Carrizo cane control project. TSSWCB sprayed 19 miles of Carrizo cane along the Rio Grande River, with permission from the private property landowner. This application will serve as a demonstration of the feasibility of spraying more acreage.
Potential benefits of improved views and surveillance of the river by the border patrol, restoration of wildlife habitat, enhancing stream flow, decreased fever tick environment and reclamation of rangeland certainly outweigh any perceived risks of herbicide applications.
“Carrizo Cane” is excerpted from the February 2017 issue of The Cattleman magazine.