3
Invasive Species in the
Sonoran Desert Region
11
INVASIVE SPECIES IN THE SONORAN DESERT REGION
Invasive species are altering the ecosystems of the Sonoran Desert Region.
Native plants have been displaced resulting in radically different habitats and
food for wildlife. Species like red brome and buffelgrass have become dense
enough in many areas to carry fire in the late spring and early summer. Sonoran
Desert plants such as saguaros, palo verdes and many others are not fireadapted and do not survive these fires.
The number of non-native species tends to be lowest in natural areas of the
Sonoran Desert and highest in the most disturbed and degraded habitats.
However, species that are unusually aggressive and well adapted do invade
natural areas. In the mid 1900’s, there were approximately 146 non-native plant
species (5.7% of the total flora) in the Sonoran Desert. Now non-natives
comprise nearly 10% of the Sonoran Desert flora overall. In highly disturbed
areas, the majority of species are frequently non-native invasives. These
numbers continue to increase.
It is crucial that we monitor, control, and eradicate invasive species that are
already here. We must also consider the various vectors of dispersal for invasive
species that have not yet arrived in Arizona, but are likely to be here in the near
future. Early detection and reporting is vital to prevent the spread of existing
invasives and keep other invasives from arriving and establishing. This is the
premise of the INVADERS of the Sonoran Desert Region program at the
Arizona-Sonora Desert Museum.
We have chosen nine invasive species to initiate the INVADERS program.
Seven of these species are invasive plants and two are animal species. The two
animal species are not yet in Arizona, but their arrival could be devastating to our
state. The nine species are:
Buffelgrass -Pennisetum ciliare
Fountaingrass - Pennisetum setaceum
Natalgrass - Melinis repens
Sahara mustard - Brassica tournefortii
Tamarisk (saltcedar) - Tamarix chinensis
Athel tree - Tamarix aphylla
Onionweed – Asphodelus fistulosus
Red imported fire ant - Solenopsis invicta
Argentine cactus moth - Cactoblastis cactorum
Information on each of these species including their identification, impact, history,
and distribution are included in the following pages of this handbook. This
information is also available on the ASDM website at
www.desertmuseum.org/invaders.
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Buffelgrass (Pennisetum ciliare)
What is it?
Buffelgrass is a shrubby grass to 1.5 feet tall and 3 feet wide. It looks like a
bunchgrass when small (either a seedling or recently burned, grazed, or cut). Older
plants branch profusely and densely at nodes, giving mature plants a messy
appearance. These nodal branches produce new leaves and flower spikes very
quickly after light rains, making buffelgrass an extremely prolific seed producer.
Some native grasses such as Arizona cottontop (Digitaria californica) branch sparsely
and do not appear shrubby. Bush muhly (Muhlenbergia porteri) is a true denselybranched shrub; it differs from buffelgrass in its very delicate texture.
An entire mature plant.
A single basal stem teased out, showing the
profuse branching above ground.
Inflorescences are 1.5 to 5 inches long, fat brown to purplish when fresh or
occasionally straw-colored. The spikes are crowded with dense bristly fruit which are
actually burs without hardened spines. (For this reason buffelgrass is sometimes
included in the genus Cenchrus, the burgrasses.) This is primarily a warm-season
grass, but below 3000 feet in our region it can grow and flower after almost any rain.
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The individual units visible in these
buffelgrass inflorescences are
basically soft burs.
The most similar native grass is plains
bristlegrass (Setaria macrostachya). The
individual seeds are clearly visible.
Why is it a Threat?
Buffelgrass grows densely and crowds out native plants of similar size. Competition
for water can weaken and kill larger desert plants. Dense roots and ground shading
prevent germination of seeds. It appears that buffelgrass can kill most native plants
by these means alone.
Tumamoc Hill in Tucson, home of the University of Arizona's historic Desert
Laboratory visible at left, has been overrun by buffelgrass in the last two decades. It
has not burned, but native plants are declining and dying from lack of water. Photos:
Travis Bean
[Red brome (Bromus rubens) is another invasive grass that has covered huge areas
of lower bajadas in the upper Sonoran Desert. This annual grass has caused serious
damage in the past several decades. It grows densely only in wetter years and
produces relatively mild fires, so fires are infrequent and don't completely kill native
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communities in one episode. Nonetheless conversion is progressing where it has
invaded.]
Buffelgrass is a very drought-tolerant perennial, so it can remain dense and even
spread in dry years. It is present to burn year round and supports hotter fires than
those of red brome. The Sonoran Desert evolved without fire as an ecological factor
and most of its plants cannot tolerate it. A single buffelgrass fire kills nearly all native
plants in its path. The buffelgrass invasion is now destroying steep hillsides
compared to red brome's flatter terrain, and is rapidly converting formerly rich
biological communities into monocultural wastelands.
A "natural" roadside with native
vegetation. AZ Hwy 85 in Organ Pipe
Cactus National Monument, where
buffelgrass is controlled.
Buffelgrass resprouts vigorously after
fires, but most native desert plants are
killed. Near Caborca, Sonora.
The shoulders of this road near Saric,
Sonora are almost 100% buffelgrass, a
common result where it isn't controlled.
Buffelgrass is abundant in the adjacent hills,
but heavy grazing keeps it from reaching
burnable density.
This hillside near Caborca, Sonora recently
burned, killing nearly all of the native
plants. Only charred skeletons of teddy bear
cholla (Cylindropuntia bigelovii) and a palo
verde (Parkinsonia microphylla) are visible.
The rich Arizona Upland vegetation that
once grew here can be seen in the distance.
There is growing evidence that buffelgrass depletes soil fertility in a decade or so. It
then dies and leaves behind a sterile wasteland. No one knows how much time will
be needed to restore such ruined land.
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Distribution
Native to the Old World where it is widespread in Africa, the Middle East, Indonesia
and nearby islands, and tropical Asia. Introduced to Australia and the New World.
In the Sonoran Desert Region buffelgrass is common in southern Arizona and most
of Sonora.
Habitat
There are two seemingly unrelated habitats in the Sonoran Desert. In valleys and
lower slopes buffelgrass invades disturbed areas such as roadsides and cleared or
grazed fields. It Arizona it is spreading very rapidly along medians and shoulders of
major highways and more slowly on smaller roads. In northern Sonora it has been
present longer, and it dominates long stretches of smaller highways. From the town
of Imuris, Sonora buffelgrass extends in a continuous ribbon along highway 15 all
the way to Sinaloa, interrupted only by a few cities.
A typical roadside habitat for buffelgrass
(under the stopsign). The larger grasses
are the related fountaingrass (Pennisetum
setaceum), which is also a serious invasive
threat.
This cleared field is nearly pure
buffelgrass. It has not dominated the
surrounding flats which have not been
cleared of vegetation.
Its other habitat is steep rocky hillsides, mostly east- and south-facing slopes. It is
most abundant on debris cones near the angle of repose. These steepest slopes may
be the best establishment sites from which it will eventually spread. Some less steep
hillsides are completely covered with buffelgrass, so the invasion may still be in its
early stages. It occurs from near sea level to 4150 feet elevation.
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Buffelgrass being censused on a
hillside near Magdalena, Sonora.
Most of the herbaceous plants have
disappeared.
A steep rocky hillside in the Pan Quemado Mts,
Ironwood Forest National Monument. Several patches of
buffelgrass are visible.
History
Buffelgrass was introduced to the United States about in the1930s as livestock
forage. It was in planting trials at the Soil Conservation Service nursery in Tucson
from 1938 to 1952. Several experimental plantings were done beginning in 1941 at
Aguila near Phoenix. Most did not do well. (Another planting in Avra Valley west of
Tucson in the early 1980s also died out where it was planted on flat ground.)
Records of collections in natural habitat were sparse until about 1980 when it began
a rapid expansion. One example is Organ Pipe Cactus National Monument, where
buffelgrass was rare before 1984 (Felger 1990). By 1994 it had occupied 20-25
square miles and was expanding rapidly. Few people other than botanists noticed it
in Arizona before 1990. Today it is difficult not to see it in the southern half of the
state.
A survey of roads done by the Desert Museum in 2004 revealed the full extent of the
buffelgrass invasion of Arizona and northern Sonora (map below).
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Buffelgrass distribution along roads in
Arizona and northern Sonora. Red
symbols in both maps denote areas
where buffelgrass is the dominant plant
and dense enough to burn.
Buffelgrass distribution in the Tucson
vicinity. The survey was not completed
within the urbanized zone; buffelgrass is
present here in nearly every vacant lot
and unpaved road shoulder.
What can be Done?
Buffelgrass can be controlled by manual pulling and herbicides. Organ Pipe Cactus
National Monument nearly eradicated patches covering ca. 25 square miles in three
years of intensive manual labor. After the initial control only minor efforts have been
required to destroy new infestations (though searching the huge park takes a great
deal of time). Volunteer groups such as Sonoran Desert Weedwackers are active in
controlling it in other areas such as Tucson Mountains Pima County Park.
The highest priority should probably be to control buffelgrass on roads outside of
urban zones, because these are the seed sources for invasion of natural habitats.
Second priority should go to the most valuable habitats such as parks.
In the long run we may need biological control. This will be a controversial issue
because buffelgrass is still valued as livestock forage. To this issue, it must be
publicized that buffelgrass is not nearly as economically viable as first thought.
Research in Africa, Australia, South America, Texas, and Sonora reveal that the
average useful life of a buffelgrass pasture is only 10-12 years. Under exceptional
management productive pastures have lasted only 15 or 16 years (Ibarra 1999).
Buffelgrass impoverishes the soil and evenually dies, leaving behind a sterile
wasteland that requires expensive efforts to restore productivity.
The public and land management agencies must be educated to recognize
Buffelgrass for the threat that it is. The state of Arizona declared it to be a noxious
weed in March 2005. On the other hand, at least one branch of the federal
government is breeding buffelgrass to develop more cold-hardy varieties.
Other common names: African foxtail grass, anjan grass, syn. Cenchrus ciliaris.
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References
Tellman, Barbara (ed.). 2002. Invasive Exotic Species in the Sonoran Desert Region.
University of Arizona Press.
Ibarra F., Fernando. 1999. Lo mejor del dia del ganadero. Summary of oral
presentation on website.
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Fountaingrass (Pennisetum setaceum)
What is it?
Fountaingrass is an attractive, robust clumping grass
that grows up to 3 ft tall and wide. Its long, wiry leaves
are 11 to 30 in long from the base and form dense, light
green clumps in summer. Together the old whitish and
the new purplish inflorescences form a halo above the
green leafy core. The cylindrical inflorescences are thick,
4 to 14 in long, round in cross-section, pink, or purplish
during colder weather, and dry white. Soft silky hairs to
over an inch long surround the fruits. This grass is most
vigorous in the warm season (July-September), but also
flowers most of the year below 3000 feet in our region.
It appears to be somewhat more cold tolerant than
buffelgrass (Pennisetum ciliare) as it reaches 4800 feet
elevation in the Santa Catalina Mountains (650 feet
higher than buffelgrass).
Photo: Mark Dimmitt
Buffelgrass is another introduced African grass in the genus Pennisetum, which is
also a serious invasive species in the Sonoran Desert Region. It differs from
fountaingrass in its smaller size (1 to 1.5 ft tall), branched stems, broad leaves and
shorter (1.5 to 5 in long) fat, brown to purplish cylindrical inflorescences growing
from nodes along the stems. Above 4000 feet, bullgrass (Muhlenbergia emersleyi) is
a 3 ft tall, clumping native species that resembles fountaingrass. Its numerous small
seeds with long (0.5 in) purplish bristles form loose, flattened, nodding banners that
are unlike the cylindrical inflorescences of fountaingrass.
Photos: Mark Dimmitt
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Why is it a Threat?
Fountaingrass is a large grass that produces lots of seeds that can spread rapidly
spreads from cultivation into nearby disturbed areas, and eventually into natural
habitats. It often forms dense stands and aggressively competes with native species,
especially perennial grasses and seasonal annuals, for space, water, and nutrients.
Fountaingrass provides lots of fuel, and is well adapted to fire. In Hawaii ,
fountaingrass fires are a serious threat to the native species. After burns, it regrows
rapidly from extensive roots. In contrast, fire is not an ecological process in the
Sonoran Desert or tropical communities to the south, and native trees, shrubs, and
succulents are decimated by fire. In the Arizona Upland, grasses often dominate
roadsides and fires are more frequent than in undisturbed habitats. Grasses that
commonly occur with fountaingrass on roadsides include the native cane beardgrass
(Bothriochloa barbinodis), plains bristlegrass (Setaria macrostachya), purple
threeawn (Aristida purpurea) , spike pappusgrass (Pappophorum vaginatum),
tanglehead (Heteropogon contortus) , the non-native barley (Hordeum murinum) ,
Bermuda grass (Cynodon dactylon) , Lehmann lovegrass (Eragrostis lehmanniana),
Natalgrass (Melinis repens), red brome (Bromus rubens), and wild oats (Avena
fatua).
Threats from fountaingrass fires are most serious in natural riparian habitats in
scenic mountain canyons. In the Tucson area, it has invaded the rocky canyons in
Finger Rock, Pima, Sabino, and other Canyons in the Santa Catalina Mountains and
King Canyon in the Tucson Mountains . Fountaingrass is less of a threat in desert
grassland or chaparral above 3500 feet where fire is a natural process.
It has been declared as a state noxious weed by Hawaii and Nevada .
Distribution
Fountaingrass is native to North Africa and the Middle East . It has been widely
cultivated as an ornamental around the world and often escapes into natural
habitats. In the United States, it is common in southern Arizona, southern California,
southern Nevada, southwestern Utah, and Hawaii . It has also been found in Florida,
Louisiana, Tennessee, Oregon, Colorado, and Texas .
In Arizona it is widespread in the Phoenix, Tucson, Ajo, and Gila Bend areas in
Maricopa and Pima counties. It is also common along the Colorado River from Lake
Mead to Parker in Mohave and La Paz counties. A few plants have been found in
Cochise, Gila, Pinal, Santa Cruz , and Yavapai counties. In the Mexican portion of the
Sonoran Desert Region, it is only beginning to escape cultivation in Alamos, Kino
Bay, and Magdalena (Sonora), near Ensenada (Baja California), and Mulegé (Baja
California Sur).
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Habitat
Fountaingrass mostly occurs on disturbed
roadsides, rocky outcrops, canyons, and
cliffs from 2000 to 3500 feet in the
Sonoran Desert Region in Arizona . It is
most common in riparian habitats within
paloverde-saguaro desertscrub in the
Arizona Upland Sonoran Desert . It is less
common in the Lower Colorado River
Valley desertscrub down to about 985
feet, and in chaparral, desert grassland,
and oak woodland up to 4800 feet. On the
Fountaingrass invading a suburban
north side of Tucson, it replaces
roadside. Photo: Mark Dimmitt
buffelgrass on roadsides and rocky road
cuts.
It is also common in another riparian habitat on flood lines and rocky shores of
reservoirs and rivers in low-elevation (400 to 1200 feet) Mohave and Sonoran
desertscrub. It is common from Lake Mead to Parker along the Colorado River in
some very hot, dry areas.
History
Although fountaingrass was reported in Hawaii as early as 1914, it was first collected
on roadsides in Arizona in the Santa Catalina Mountains (4500 ft elevation) and in
Ajo in 1940. It was used in urban landscapes in Tucson as early as 1940, and
cultivated in the Soil Conservation Nursery (now National Resource Conservation
Service) in 1941. It was well established in the Santa Catalina Mountains by the
1940's and the Phoenix area by 1962. Later specimens were collected in nowprotected natural areas in the Tucson area including Tumamoc Hill (1968), the
Arizona-Sonora Desert Museum (1966), and King Canyon (1988) in the Tucson
Mountains, and Sabino Canyon (1974) in the Santa Catalina Mountains. Like
buffelgrass, it has expanded dramatically in many areas since 1990.
What can be Done?
Poorly-maintained nurseries can be
sources of new invasive weeds.
Fountaingrass in this nursery is in seed
and can soon invade surrounding land.
Fountaingrass can be controlled by
physically removing the entire plant,
including the seed-bearing inflorescences.
Seedlings and small plants can easily be
pulled by hand. Iron digging bars or
shovels will help extract larger plants. It
may be necessary to return to controlled
areas for several years to remove
seedlings. Chemical treatments with
systemic herbicides may be needed to
control large infestations. Herbicides have
been sprayed from boats to control
fountaingrass along rocky shorelines of
Colorado River reservoirs.
There are alternatives for fountaingrass in
urban landscapes. Bronzeleaf
fountaingrass (var. cupreum) is a
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genetically-modified sterile cultivar that can be planted instead of the normal plants.
Native grasses that resemble fountaingrass but are not invasive include bullgrass
and deergrass (Muhlenbergia rigens). Beargrass (Nolina microcarpa) and desert
spoon (or sotol, Dasylirion wheeleri) are native succulents that grow in large clumps
that are attractive in desert gardens and road medians.
Links
California Exotic Pest Plant Council:
http://ucce.ucdavis.edu/files/filelibrary/5319/17411.pdf
Pima County Exotic Species Council: www.co.pima.az.us/cmo/sdcp/
National Resource Conservation Service, National Plant Data Center , USDA. 2004.
The PLANTS Database, Version 3.5:
http://plants.usda.gov/cgi_bin/plant_profile.cgi?symbol=PESE3
Plant Conservation Alliance, Alien Plant Working Group:
www.nps.gov/plants/alien/fact/pesel.htm
References
Tellman, Barbara (ed.) 2002. Invasive Exotic Species in the Sonoran Desert .
University of Arizona Press.
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Natalgrass (Melinis repens)
What is it?
Natalgrass (synonym Rhynchelytrum roseum) is an erect grass to 28 in tall that has
attractive long reddish or pink silky hairs on the triangular fruit at maturity, fading to
silvery white with age. In the northern part of its geographic range, it is short-lived
perennial or annual, but becomes stouter in warmer areas to the south. The
branched inflorescences are open (2-3 in wide) and fluffy. The leaves are narrow and
flat (3-8 in long) from unbranched stems. It can flower throughout the year under
favorable temperature and moisture conditions but is limited by hard freezes.
Photo: T.R. Van Devender
Photo: Mark Dimmitt
Bush muhly (Muhlenbergia porter) is a native species with pink inflorescences but
differs from Natalgrass in its sprawling growth habit and tiny pink seeds in nebulous
clusters growing from stem nodes. Arizona cottontop (Digitaria californica) also has
white silvery hairs but the fruit are flattened, oval, and in slender spikes rather than
open panicles.
Why is it a Threat?
In most areas in the Tucson vicinity,
Natalgrass mainly occurs on roadsides
and does not present a serious threat to
natural ecosystems. But in eastern and
north-central Sonora it left the roadsides
and invaded natural grassland habitats
beginning about 1990. As with Lehmann
lovegrass (Eragrostis lehmanniana),
weeping lovegrass (E. curvula), King
Ranch bluestem (Bothriochloa
ischaemum), and other non-native forage
grasses in Arizona, the introduction of
Natalgrass has recently taken over this
Natalgrass results in changes in the
hillside near Yécora, Sonora. Photo: T.R. composition and structure of desert
Van Devender
grassland, but not conversion to
desertscrub or some other type of
vegetation. In contrast to buffelgrass (Pennisetum ciliare), it does not appear likely
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to invade drier desert habitats in the Sonoran Desert Region in patches dense
enough to burn and convert desertscrub to savanna-like grassland. In Hawaii and
some areas on the Mexican Plateau north of Mexico City, recurrent fires in dense
Natalgrass stands threaten natural vegetation and native species. It is listed as an
alien pest species in Hawaii.
South of Nogales, Sonora, dense
Natalgrass stands along the highway
right-of-way burns regularly. In one area,
a fire spread up a grassland slope and
burned hop bush (Dodonaea viscosa) and
other shrubs to the ground. It has
colonized the canyon bottom and is
invading the adjacent south-facing slopes
of Pima Canyon in the Santa Catalina
Mountains near Tucson. In the Mule
Mountains five miles west of Bisbee in
southeastern Arizona, it grows densely
with velvet mesquite (Prosopis velutina)
Natalgrass fire in highway median, south
and ocotillo (Fouquieria splendens) in
of Nogales, Sonora. Photo: T.R. Van
desert grassland on a south-facing slope Devender
very similar to those south of Nogales. It
is intolerant of cold and dies back to the base at the first frost. Cold temperatures
probably prevent it from expanding into many higher or more northern areas in
Arizona. However, its behavior in warmer areas to the south suggests that it is
prudent to watch it in the southern Arizona borderlands where many tropical plants
and animals reach their northern distributional limits.
Distribution
Natalgrass is native to South Africa but is now introduced in the warmer parts of the
world, including tropical Latin America in North and South America. In the United
States it is mostly found in Florida, west along the coast of the Gulf of Mexico to
south Texas, southern Arizona, and Hawaii. It also occurs in Maryland, Virginia, New
Mexico, southern California, Puerto Rico, and the Virgin Islands. In Sonora, zacate
rosado is common in the Nogales-Imuris area (north-central) and from Tepoca to the
Yécora-Maycoba area (eastern). It is locally present in Sonoran Desert in central and
west-central Sonora, and southward and eastward into more tropical areas.
In Arizona Natalgrass is locally common in Pima County in the Santa Catalina and
Tucson Mountains, and Tucson, and in Cochise County in the Mule Mountains west of
Bisbee. It is uncommon in Santa Cruz County in the Santa Rita Mountains.
Habitat
Natalgrass is most common in Arizona on disturbed roadsides along paved highways
in desert grassland 3000 to 4000 feet. In eastern and northern Sonora, and in the
Mule Mountains west of Bisbee, it has spread into natural desert grassland. It is less
common in the Arizona Upland Sonoran Desert down to 2400 feet and oak woodland
up to 5700 feet.
In Sonora, it is common in desert grassland northeast of Imuris and south of Nogales
(to 4300 feet), and near Maycoba in the Sierra Madre Occidental in eastern Sonora
(to 5400 feet). It occurs in desertscrub, foothills thornscrub, and tropical deciduous
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forest from near sea level in the Guaymas area through the transition into oak
woodland (3600 feet) above Tepoca in eastern Sonora.
History
This attractive grass with its long purplish-pink, silky hairs on the fruit and open
inflorescences has been grown as an ornamental. It was grown for forage in the
southeastern United States. In the Arizona Flora published in 1951, Natalgrass was
only reported in Pima County in the Santa Catalina Mountains near Tucson. Since
that time it has spread into many areas in the Tucson area and appears to be
expanding its range in the Arizona-Sonora borderlands.
What can be Done?
Management and control methods are not well known. It should not be planted as an
ornamental and should be pulled by hand in areas of conservation concern.
Other Common Names: rose Natalgrass, Natal redtop, zacate rosado, espiga
colorada, pink feathergrass, rubygrass, Holme's grass, blanketgrass.
Links
Utah State University Intermountain Herbarium Grass Manual (distribution map in
the United States)
USDA Natural Resources Conservation Service Plants Profile
Fact sheet on Natalgrass in the Pacific Islands
References
Gould, F. W. 1977. Grasses of the Southwestern United States. University of Arizona
Press, Tucson.
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Sahara mustard (Brassica tournefortii)
What is it?
Numerous Old World mustards have invaded North America. Of these Sahara
mustard (aka several other names) is the newest and by far the worst. It is a robust,
fast-growing, drought-tolerant winter annual that prefers sandy soils. The basal
rosette of divided hairy leaves can span three feet in wet years. The nearly leafless
flowering stems branch profusely and grow to a height of about two feet, creating
the appearance of a shrub from a distance. The small light yellow flowers are selfpollinating, so each of the thousands of them sets a seed pod. Large plants produce
up to 9000 seeds. Dried plants break off at the base and tumble like Russian thistle
(tumbleweed, Salsola tragus), spreading seeds rapidly across the landscape. When
wet, the seeds are sticky with mucilage and can be transported long distances by
animals and perhaps vehicles.
All photos: Mark Dimmitt
Several other exotic mustards are also invasive threats to the Sonoran Desert. Most
of them have been here a long time and have already invaded most suitable habitat;
we can hope they will not cause further damage to communities. Black mustard
(Brassica nigra and similar spp.) can also grow to nearly three feet tall. It is
distinguished from Sahara mustard by its smaller leaves and larger, bright yellow
flowers. London rocket (Sisymbrium irio) is a major pest in gardens as well as
roadsides and undisturbed desert areas. It has bright shiny leaves and flower stalks
up to 2 feet tall with small bright yellow flowers.
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Arugula (aka rocket salad, Eruca vesicaria
sativa) is a culinary herb with one-inch
whitish to yellowish fragrant flowers. The
plants can grow to 5 feet tall in wet years
as in the image at right. It is now the
dominant plant in much of the area along
Interstate 8 from Gila Bend west to the
Maricopa County line, a distance of 45
miles. Along this stretch it extends on
both sides of the freeway as far as the
eye can see. It has been there for many
decades and is apparently spreading
slowly. Because of the stealthy spread
and its remote location, its invasion has
gone largely unnoticed except by
botanists. Though a significant local
threat, arugula is a minor problem
compared to Sahara mustard.
Almost everything visible in this scene is
arugula. The plants are nearly as tall as
the widely-scattered creosotebushes
barely visible in this scene taken in March
2005.
Why is it a Threat?
This dune evening primrose seedling
(Oenothera deltoidea, right) will soon be
overgrown by the Sahara mustard
seedlings next to it.
Sand verbena (Abronia villosa) struggling
to survive beneath a large Sahara
mustard that germinated at the same
time.
This weed grows very fast, smothering native herbaceous plants and even competing
with shrubs for light and soil moisture. The famous wildflower fields of the sandy
valleys of Lower Colorado River Valley Sonoran Desertscrub are in danger. In the
winter-spring of 2005 about three-quarters of the prime display areas were overrun
with Sahara mustard in California and Arizona. Fortunately it does not do well in
every year. It is known that a freeze can kill the plants and give native flowers a
chance to grow and reproduce. However, freezes are uncommon in the low desert.
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Now: 2005
Then: 1998
What we have lost: These two scenes were both photographed in the northern end
of the Mohawk Dunes in western Arizona. In 2005 Sahara mustard covered 70-90%
of the surface area at this location. Almost no native wildflowers bloomed here in
2005.
In wet years Sahara mustard covers the ground almost 100% and can carry fire
when it dries. It is a frightful thought that hyperarid desert, including sand dunes,
can burn because of this weed. There have already been documented fires in the
dunes west of Blythe, CA and the Pinta sands in the Cabeza Prieta Wildlife Refuge.
This latter site is a remote, uninhabited, and previously pristine habitat. Most
Sonoran Desert plants cannot tolerate fire; burned areas become wastelands of
nearly pure Sahara mustard.
Snow Creek Canyon on the south side of
the San Jacinto Mountains near Palm
Springs, CA used to be covered in huge
carpets of pink, yellow, and white flowers
in wet springs. Now it is almost 100%
Sahara mustard.
This area of sand dunes in the Chuckwalla
Valley, CA (west of Blythe) burned, killing
most of the creosotebushes. Sahara
mustard was the fuel.
This is the worst invasive plant in the Sonoran Desert in terms of area covered
and damage inflicted on the biotic community. In riparian communities saltcedar is
its rival.
Distribution
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Sahara mustard is abundant in the Desert Southwest at low and mid elevations from
southeastern California to southern Nevada and south into Baja California and
Sonora. It's rare in southern New Mexico and western Texas. It extends to the edge
of the tropics in Mexico.
It is native to many areas of the Old World from north Africa and the Middle East
east to southern Europe and Pakistan.
Habitat
It is most abundant in Lower Colorado River Valley Sonoran Desertscrub and lower
Mohave Desertscrub. It's currently uncommon in Arizona Upland Sonoran
Desertscrub, and rare in chaparral and desert grassland. It favors sandy, disturbed
soils at low elevations, but its range is expanding rapidly into undisturbed soils
including rocky hillsides in Arizona Upland. The literature lists its elevational range as
250 to 2800 feet, but it has recently been found above 4100 feet.
One way that weeds invade new habitats:
This huge field of dried Sahara mustard
This mound of imported soil in Tucson, AZ
near very arid Parker, AZ was several
was infested with seeds of Sahara
miles long. If it catches fire, the houses in mustard and London rocket.
the background are at risk as well as the
few native plants left.
History
This recent invader probably arrived in North America as a contaminant in crop seed.
The first record is from California's Coachella Valley in 1927. It was first discovered
in Arizona-Sonora in 1957 on Mexico Highway 2 near Yuma. By the 1970s it was
widespread in the low desert in Arizona, California, Baja California, and Sonora. It
doesn't seem to have caused much alarm until the early 1990s when people began
to realize how much habitat it was overrunning.
Sahara mustard was first collected in Tucson in 1978, and in 1991 was reported as
rare. Today it is widespread and locally common in the metropolitan area and
surrounding suburbs.
What can be Done?
In small areas Sahara mustard can be eradicated by pulling plants before they
mature seed. This is most effective in new invasions where a seed bank has not been
established.
30
Control in the thousands of square miles of remote desert habitat seems almost
hopeless. It is unlikely that a biological agent, if found, would be approved because
many important crop plants are in the genus Brassica (e.g., cabbage, cauliflower,
broccoli, brussels sprouts). There are also numerous native mustards that might be
threatened by a biological agent.
In selected areas herbicide treatment may be effective. Sahara mustard tends to be
the first annual to germinate after a rain, so early treatment may reduce its
abundance and allow later-germinating natives to establish.
The spread of Sahara mustard can be reduced by controlling it along roads, which
provide corridors for rapid invasion into new habitats.
Other Common Names: Asian mustard, Moroccan mustard, desert mustard,
southwestern mustard, Mediterranean mustard, Mediterranean turnip, wild turnip,
prickly turnip, turnip weed.
References
Felger, R.S. 1990. Non-native plants of Organ Pipe Cactus National Monument. Tech.
Rep. 31. Tucson: Cooperative National Park Research Studies Unit.
Felger, R.S. 2000. Flora of the Gran Desierto and Rio Colorado of Northwestern
Mexico. Tucson: University of Arizona Press.
Minnich, R.A. and A.C. Sanders. 2000. Brassica tournefortii Gouan. In: Bossard, C.C.,
J.M. Randall, and M.C. Hoshovsky. eds. Invasive Plants of California's Wildlands.
University of California Press, Berkeley and Los Angeles. 360 pp.
Tellman, Barbara (ed.). 2002. Invasive Exotic Species in the Sonoran Desert Region.
University of Arizona Press.
Van Devender, T.R., R.S. Felger, and A. Burquez M. 1997. Exotic Plants in the
Sonoran Desert region. 1997 Symposium Proceedings, California Exotic Pest Plant
Council. Website
31
Tamarisk, saltcedar, athel tree (Tamarix spp.)
What is it?
Tamarisk is a general term for several species of Old World shrubs and trees in the
genus Tamarix with scalelike leaves on very thin terminal twigs.
Saltcedars are large shrubs or small trees 8-16 feet tall and usually less wide. They
have tiny, triangular, scale-like leaves that are winter-deciduous. The flowers are
pink to near-white, densely crowded along branched terminal spikes; they appear
from January to October. Fruit and seeds are tiny, brown, inconspicuous. The several
species introduced to North America have been labeled Tamarix chinensis (our
current choice for southern Arizona plants), T. ramosissima, T. pentandra, T.
parviflora, and T. gallica. They are very similar in appearance and are hybridizing, so
distinguishing among them is difficult. Apparently the hybrid populations are the
most invasive.
Young saltcedar (Tamarix cf. chinensis) in
flower. Photo: Steve Dewey, Utah State
University; www.forestryimages.org
Tamarix chinensis branch with flowers. The
tiny triangular leaves stick out from the stems,
giving the twigs a prickly feel. Photo: T.R. Van
Devender
Athel tree (Tamarix aphylla, also called saltcedar) is a large evergreen tree to 50 feet
tall and wide with virtually no leaves (reduced to tiny scales) and inconspicuous
whitish flowers. It was long thought to be sterile and therefore at most mildly
invasive, but it is reproducing from seed in some localities. It has been doing so at
Lake Mead for 30 years, and is hybridizing with the deciduous saltcedars.
32
A young-mature athel tree at Lake Mead.
Photo: Elizabeth Powell
Closeup of athel tree twigs showing the tiny
scalelike leaves and small white flowers.
Photo: Mark Dimmitt; inset: Elizabeth Powell
Australian pines (Casuarina spp.) could be confused with tamarisks. They have
similar thin branches and scale-like leaves. Casuarinas don't seem to be invasive in
the southwestern U.S., where they are found mostly in landscaped areas.
Why is it a Threat?
Tamarisks are extremely invasive in riparian communities, often nearly completely
replacing native vegetation with impenetrable thickets. They are extremely
competitive against native vegetation because they are aggressive usurpers of
water. They also sequester salt in their foliage, and where flooding does not flush out
soil salts the leaf litter increases the salinity of soil surfaces. Dense stands of
saltcedars support lower biodiversity than the natural communities they displace.
This stretch of Tonto Creek above
Roosevelt Lake in Arizona is choked with
Tamarix chinensis. Most of the green on
the valley floor is this saltdecar. Photo:
Mark Dimmitt
Several miles of Greene Wash south of
Casa Grande, AZ is dominated by athel
trees. These may have propagated by
pieces of branches that wash downstream
in floods and take root, or they may be
seeding. Natural washes in this region are
vegetated by desert ironwood trees
(Olneya tesota) and blue palo verde
(Parkinsonia florida). Photo: Mark
33
Dimmitt
Distribution
Tamarisks are almost throughout the Southwest below about 6000 feet elevation. In
Arizona they are widespread, especially south of the Mogollon Rim and in the Grand
Canyon.
Habitat
Tamarisks occur mostly on low ground where water collects. They are most abundant
in riparian habitats, both natural and artificial, often in extensive pure stands. They
are less common in drier places. They thrive in alkaline and saline soils.
History
Various species of tamarisks were in cultivation in the United States in the early
1800s. The National Arboretum released T. pentandra in 1870. Tamarisk was first
noticed to be escaping from cultivation in 1880, and by the end of the century it was
common along southern Arizona and Texas rivers.
What can be Done?
There are teams of "tammywackers" in several states that are making progress in
local areas. Specially modified jacks are used to grip and pull trees up by their roots.
Cutting and treating the stumps with herbicides gives good control. Aerial spraying is
being used in large areas where tamarisks have completely taken over. In areas too
large or too remote for manual control, flood management can reduce the
dominance of saltcedars. Periodic floods prevent saltcedars from forming dense
thickets, permitting native trees and substory plants to establish and maintain
codominance.
References
Gaskin, J.F. and P.B. Shafroth. 2005. Hybridization of Tamarix ramosissima and T.
chinensis (saltcedars) with T. aphylla (athel) (Tamaricaceae) in the southwestern
USA determined from DNA sequence data. Madroño 52(1):1-10.
34
Onionweed (Asphodelus fistulosus )
What is it?
Onionweed is an herbaceous perennial in the lily
family (Liliaceae) to about a foot tall and almost as
wide. Clusters of long, tapering, round, hollow
leaves very much resemble chives or scallions.
Leaves sprout after winter rains. Flowers appear in
spring. Plants die to the ground during dry season.
The flat flowers are less than a half-inch across and
have six petaloid parts, each white with pink center
line. They are sparsely distributed on branched
spikes to almost two feet tall.
Fruits are 1/8-inch round capsules.
Mature plant in flower. Photo:
Mark Dimmitt
Onionweed might be confused with some native
onions (Allium spp.) Allium macropetalum (desert
onion) is a much shorter plant with leaves rarely
more than four inches tall. Taller native onions grow
in different habitats than onionweed.
Closeup of flower. Photo: Mark Dimmitt
Dried plant with seed capsules. Photo:
USDA
Why is it a Threat?
Onionweed is an aggressive invasive species. Introduced as an ornamental, it easily
escapes cultivation into surrounding unirrigated land. It seeds prolifically and can
establish large populations quickly. It is unpalatable to cattle and apparently to most
wildlife, so it is very persistent once established. To date it tends to invade
disturbed ground, so it is unclear whether it will be a threat to natural communities.
35
Distribution
Native to southern Europe, Mediterranean Africa, and Western Asia. In the United
States onionweed occurs in California (in several coastal southern counties), Arizona,
New Mexico, and Texas. Also known to be in Mexico. It is a noxious weed causing
problems in Australia. Arizona infestations are primarily in the southeastern corner of
the state. A few small infestations have been found in Tucson. Reported but
unverified in Ajo.
Habitat
In the Sonoran Desert region this weed
seems to do best in areas above the
desert that receive moderate winter
rainfall. A well-established population in
suburban Tucson was reduced to only two
plants after the severe drought of 2002.
Plants have been found in Arizona from
about 2000 feet elevation to at least 4500
feet.
History
Onionweed invading a roadside in
Plants introduced into the United States in southeastern Arizona. Photo: USDA
the 1980s may be the founders of our
invasion. They were offered for sale in Alpine, Texas and Phoenix, Arizona as early as
1984. Some of the original US plants were collected from a naturalized population
near Saltillo, Coahuila, Mexico, where the species was documented in 1930.
What can be Done?
Some nurseries offer onionweed as an
ornamental even though it is a prohibited
noxious weed in many states as well as a
federally listed noxious weed. Do not buy
it or plant it, and eradicate it if it is
established on your property.
Pulling the plant is usually not effective.
The top breaks off leaving the tuberous
roots underground. They must be dug up
by the roots or sprayed with herbicide.
A flowering plant in desert grassland with mesquite. Other common names: pink asphodel,
hollow-stemmed asphodel
Photo: USDA APHIS Archives,
www.forestryimages.org
36
Links
USDA Plant Database Profile
InvasiveSpecies.org onionweed page
The Nature Conservancy's Invasive Species Initiative
References
(The literature on this species is very sparse
37
.)
Red Imported Fire Ant (Solenopsis invicta)
What is it?
The red imported fire ant (RIFA) is a small reddish brown ant from South America .
There are six known species of fire ants (Solenopsis spp.) in the United States, three
of which are found in Arizona. These three species are the southern fire ant (S.
xyloni), and two species of desert fire ant (S. aurea and S. amblychila). RIFA has not
established in Arizona, but is present in the bordering states of New Mexico and
California. It was discovered near Yuma, Arizona but was exterminated.
Adult red imported fire ants. Photo: USDA RIFA workers marked with wire bands.
APHIS PPQ Archives,
Photo: Bart Drees
www.forestryimages.org .
RIFA are small but highly aggressive. They inject a necrotising, alkaloid venom when
they sting. The stings result in painful, itchy, and persistent pustules, and sometimes
in severe allergic reactions. Five million people are stung each year in the
southeastern United States. About 25,000 of these people require medical
consultation. When a fire ant mound is disturbed, workers boil to the surface, run up
any legs, arms, etc. in the vicinity, grab the victim's skin in their mandibles and sting
synchronously in response to the slightest movement. The attacks are coordinated
and dozens or even hundreds of workers sting in unison.
Fire ants swarming boot after mound
disturbance. Photo: Bart Drees.
Pustules from RIFA stings. Photo: Murray
S. Blum, The University of Georgia,
www.forestryimages.org
38
Fire ants live in colonies that may have 100,000 to 500,000 ants. The queen of the
colony can lay from 1500 to 5000 eggs per day, never leaves the nest and can live
for many years. Worker ants take care of the queen and her eggs, build the nest,
defend the colony, and find food. Preferred food of fire ants consists of protein-rich
sources such as insects and seeds. Winged male and female ants fly from the colony
in the spring and summer to mate in the air. The males die and the females become
queens that start new colonies.
Only the red imported fire ant has a median clypeal tooth and a striated
mesepimeron; these may be difficult to see at first. RIFA also have an antennal
scape that nearly reaches the vertex, a post-petiole that is constricted at the back
half, and the petiolar process is small or absent. Of the native fire ant species, the
southern fire ant (Solenopsis xyloni) looks the most like the red imported fire ant. It
can be identified by its brown to black color, well-developed petiolar process, and no
median clypeal tooth. Desert fire ants (Solenopsis aurea and S. amblychila) are both
yellowish-red to reddish-yellow and have a well-developed petiolar process. RIFA can
also be identified by the proportion of large to small workers in disturbed mounds. If
half the workers in disturbed mounds are large and dark, it is RIFA. If only a few
large ants appear relative to hundreds of small ants, it is non-RIFA.
Side view of adult RIFA worker. Photo:
USDA APHIS PPQ Archives,
Median clypeal tooth can be seen here on
www.forestryimages.org.
head above the mandibles. Mandible has
4 teeth. Photo: Carl Olsen
39
Table: Characteristics of RIFA and RIFA mounds
Characteristic
Description
RIFA
# of node segments
2
# of sizes of workers
Many (polymorphic)
Size of workers
3 – 7 mm
Shape of thorax
Uneven
# of antennal segments
10 with two-segment club at tip
# pairs of spines in thorax
None
Color
Reddish brown, abdomen darker
Stinger
Present, inflicts pain, leaves white pustule (pustule is not an
allergic reaction)
Mound
Material
Formed from excavated soil
Size
Wider than a dinner plate at its base
Shape
Amorphous, often oval shaped like a mountain cone
Visibility
Above ground, 4” to 24” tall
Entrance
None visible, ants access mound through subterranean tunnels
that spoke out from the central mound
Texture
Has a fresh-tilled appearance, especially after a rain
Size variation in RIFA worker ants and
queen on the right. Photo: S. Porter.
RIFA mounds have a fresh tilled
appearance. Photo: Bart Drees.
Why is it a Threat?
RIFA colonies are extremely destructive. They dominate their home ranges due to
their large numbers and aggressiveness. The lack of natural enemies results in
population booms in areas they invade.
40
RIFA alter the composition of the ecological communities in the areas they invade.
They outcompete and frequently eliminate native fire ants. They also compete with
other animals for food and alter abundance of prey species. RIFA attack eggs and
young of many bird and reptile species. In areas of high infestation, RIFA have
significantly reduced northern bobwhite quail populations (Allen et al. 1995) and may
completely eliminate ground-nesting species from a given area (Vinson and Sorenson
1986). They also attack small mammals such as rodents and have been known to
attack and sometimes kill newborn deer and cattle. Due to a 10-20 year lapse before
bird population reductions are observed, it is suggested that actual effects of RIFA on
animal populations may be underestimated (Mount 1981). Natural plant ecosystems
could potentially be impacted as well. RIFA predates upon solitary bees that are
pollinators of certain plants (Vinson 1997) and move and feed on large quantities of
seeds.
Tricolor heron chick being attacked by fire RIFA feeding on plant nectar. Photo: S. B.
ant workers. Photo: Bart Drees.
Vinson.
Stings from RIFA create health problems for many humans. Fire ants sting
repeatedly and venom is injected from the poison sac with each sting. RIFA venom
has a high concentration of toxins that cause an intense burning and itching that
lasts for an hour and is followed by a blister that becomes a white pustule. Broken or
scratched pustules can result in secondary bacterial infections and permanent scars.
In some individuals, severe allergic reactions can occur resulting in anaphylactic
shock and even death (Dowell et al. 1997).
RIFA worker biting and stinging human.
Photo: Texas Department of agriculture
file photo.
Secondary infection following RIFA sting
on hand. Photo: Texas Department of
Agriculture file photo.
41
RIFA cost the US billions of dollars a year in damage to agricultural crops and
equipment, livestock, wildlife, public health, and electrical equipment such as air
conditioners, traffic signal boxes, electrical and utility units, telephone junctions,
airport landing lights, electric pumps for oil and water wells, computers, and even
car electrical systems. Control methods for RIFA are extremely costly.
Fire ant mound in electrical utility
housing. Photo: S. B. Vinson.
RIFA in traffic control relay switch box.
Photo: Bart Drees.
Distribution
RIFA are native to South America and were brought to the US sometime around the
1930's. They now occupy more than 275 million acres of land in the US and are
found in Florida, Georgia, Alabama, Mississippi, Arkansas, South Carolina, North
Carolina, Texas, Louisiana, Tennessee, New Mexico , Oklahoma, and California. They
invade via transported nursery stock, honeybee colonies, and on empty trailers and
trucks. Cold temperatures may limit the northward spread of RIFA in the US and the
westward spread may be limited by drier conditions. Natural dispersal occurs on
flowing water. Areas with seasonal flooding are vulnerable to RIFA invasion.
RIFA colony floating in flood water. Photo: RIFA colony emerging from flood water.
Bart Drees.
Photo: Bart Drees.
Habitat
In infested areas, colonies are common in lawns, gardens, school yards, parks,
roadsides, and golf courses. Nests generally occur in sunny, open areas and are most
common in disturbed and irrigated soil. RIFA mounds are 4 to 24 inches tall and
have no visible surface entrance. Mounds are accessed through subterranean tunnels
42
that spoke out from the central mound. Non-RIFA mounds rarely exceed an inch or 2
in height. RIFA mounds have a fresh-tilled appearance, especially after a rain.
Typical RIFA mound. Photo: USDA APHIS
PPQ Archives, www.forestryimages.org .
Profile diagram of RIFA mound. Photo:
Texas Cooperative Extension file photo.
History
RIFA are believed to have arrived in the southern United States around the 1930's on
ships from South America as ballast waters were dumped or goods were unloaded.
Their range expanded rapidly and today they occupy 13 US states and Puerto Rico .
What can be Done?
RIFA is a regulated species in Arizona. To keep RIFA out of Arizona, the Arizona
Department of Agriculture has been conducting surveys at high-risk sites such as
nurseries, parks, truck stops, etc. In 2004, all samples collected were negative for
RIFA. The drier climate in Arizona is a limitation for this species, however, as we
irrigate more lawns, agricultural fields, and golf courses, we increase our chances of
a successful RIFA invasion. Once RIFA has established in an area, the chances of
eradicating it are slim and control becomes the primary means of fighting its spread.
It is vital that we prevent the spread of this species. RIFA very easily travel in potted
plants and soil and in our vehicles. If RIFA is detected, citizens should contact the
Arizona Department of Agriculture for confirmation and eradication. Eradication
methods are complex due to the life cycle of the species and should be conducted by
trained individuals.
Links
Arizona Department of Agriculture Red Imported Fire Ant Update
Invasivespecies.gov – a gateway to Federal efforts concerning invasive species
Texas Imported Fire Ant Research and Management Project
University of Florida Red Imported Fire Ant Site
US Department of Agriculture APHIS Imported Fire Ant Information
43
References
Allen, CR, Lutz RS, and Demarais S. 1995. Red imported fire ant impacts on northern
bobwhite populations. Ecological Applications 5(3):632-638.
Dowell, RV, Gilbert, A, and Sorenson J. 1997. Red imported fire ant found in
California . California Plant Pest and Disease Report 16(3-4) June-September: 50-55.
Mount RH. 1981. The red imported fire ant, Solenopsis invicta (Hymenoptera:
Formicidae) as a possible serious predator on some southeastern vertebrates: direct
observations and subjective impressions. Journal fo the Alabama Academy of Science
52:71-78.
Vinson SB. 1997. Invasion of the Red Imported Fire Ant (Hymenoptera: Formicidae)
Spread, Biology, and Impact. American Entomologist 43(1):23-29.
Vinson SB, Sorenson, AA. 1986. Imported Fire Ants: Life History and Impact. The
Texas Department of Agriculture. P.O. Box 12847 , Austin , Texas 78711 .
44
Argentine Cactus moth (Cactoblastis cactorum)
The adult cactus moth is not distinctive; there
are thousands of species of small brown moths.
The egg sticks and larvae, however, are easy to
recognize. Photo: Susan Ellis, USDA APHIS PPQ
www.forestryimages.org
Prickly pear pad hollowed out by larvae of the
Argentine cactus moth. Photo: Les Tanner,
Northwest Weeds, www.forestryimages.org
What is it?
The Argentine Cactus Moth (aka Cactoblastis cactus moth) is a small (22-35 mm)
grayish-brown moth. The larvae are 25-30 mm in length and bright orangish-red
with large dark spots that form cross bands. In Florida there can be three
generations in a year. The eggs are laid in a series of up to 140 that creates a chain,
looking like a stick or spine on the surface of the prickly pear pad (cladode). Upon
hatching the larvae burrow into the pad and begin feeding gregariously on the
tissues. This feeding consumes the cladode completely and the larvae move to other
ones before pupation.
The distinctive "egg stick". Photo: Susan Ellis,
USDA APHIS PPQ www.forestryimages.org
Larvae inside a prickly pear pad. Photo: Susan
Ellis, USDA APHIS PPQ www.forestryimages.org
Why is it a Threat?
As a natural feeder on prickly pears (Opuntia species) the caterpillars of this moth
are capable of destroying plants and populations of these plants. Prickly pear cacti
are popular in residential and commercial landscapes throughout the southwest US
and Mexico . Additionally there is widespread and valuable commercial and
traditional use of the plants in Mexico. Opuntia production of food for humans and
45
livestock are the major uses. It is estimated between 2% of the value and production
from agriculture in Mexico is from Opuntia.
Top left: A field of prickly pears (Opuntia ficus-indica) being grown for nopales (edible pads) or tunas (edible fruits)
near Hermosillo, Sonora. Top right and bottom left: Tunas for sale in Hermosillo market. Bottom right: Tunas
prepared to eat. Photos: T.R. Van Devender
Widespread invasion by this moth could lead to extensive destruction of natural
Opuntia populations that serve as food for wildlife such as deer, javelina, rodents,
and coyotes. Birds use prickly pears as nesting sites.
Distribution
The moth is native in the South American countries of Argentina , Brazil , Paraguay
and Uruguay.
It was introduced into Australia in 1926 as a control for the invasive spread of prickly
pears that had been introduced as animal fodder. Introduction has occurred in
African, Asian and island countries since then.
46
The arrival in Florida may have natural dispersion from the West Indies or on
imported plants.
Habitat
Suitable habitat in the U.S. has not been
determined. It can live on many species
of prickly pears, but it is not known
whether it can tolerate the arid climate of
the Southwest.
If Cactoblastis can invade the Sonoran Desert,
prickly pears will virtually disappear from the
landscape. Photo: Mark Dimmitt
History
The moth is native to several South American countries. It was discovered in the
Florida Keys in 1989 and has now spread north to South Carolina and east into
Alabama
What can be Done?
Monitoring Opuntia in nurseries and home landscapes in the path of expansion of the
range of Cactoblastis for evidence of infestation will be critical for early detection.
Research into control methods is being conducted, looking at chemical, biological and
sterile insect techniques (SIT).
Control by available insecticides may be appropriate in nursery and small landscape
settings, but not in widespread landscapes or agriculture.
Specific Biological Control agents (predators) have not been identified and study in
the home range of the moth is continuing.
Sterile Insect Techniques is a process of releasing sterile males into a population,
they breed with fertile females resulting in sterile eggs, thus fewer offspring.
Studies with this technique will take place in 2005.
47
The oozing wounds on this prickly pear pad are
symptomatic of several species of cactus borers,
not necessarily Cactoblastis. Photo: USDA
This saguaro seedling is infested by the native
blue cactus borer (Cactobrosis fernaldialis). The
larva of this moth is bluish in color and do not
feed in colonial groups. This native rarely causes
lethal damage to larger cacti. Photo: Mark
Dimmitt
Links
National Invasive Species Council " invasive species of the month" for March 2005
University of Florida Featured Creatures: the cactus moth
European and Mediterranean Plant Protection Organization (EPPO)
References
Solis, M. Alma, Stephen D. Wright and Doria R. Gordon. 2004.
Tracking the Cactus Moth Cactoblastis cactorum Berg.as it flies and eats its way
westward in the US .
News of the Lepidopterists' Society, Vol. 46 Number 1.
Soberon, J., J. Golubov, and J. Sarukhan , 2001.
The Importance of Opuntia in Mexico and Routes of Invasion and impact of
Cactoblastis cactorum (Lepidoptera: Pyralidae).
Florida Entomologist 84 (4).
48