This site is provided as an introduction to biological control
of weeds in Texas. Basic information about the target weeds is provided.
Insects and mites that have been introduced into Texas as agents
for biological control of weeds are included and are the focus of
this site. The use of grass carp as an agent to manage nuisance
aquatic weeds is mentioned for completeness although most of the
information about this agent should be acquired from Texas
Parks and Wildlife. Disease organisms as agents for biological
control of weeds has not been included.. There are few examples
of disease organisms that have been used as biological control agents
for weeds. For more information, you should review the web page
links provided. The literature cited sections provide citations
that will server as an introduction to the scientific literature.
Biological Control of Weeds in Texas
Texas has an interesting, although rather brief, history of involvement
with biological control of weeds. Releases of insects for biological
control to manage aquatic weeds in Texas began in the early 1960's.
The introduction of Agasciles hygrophila, a flea beetle,
to control alligatorweed was probably the first program. This beetle
can quickly build up in numbers and locally reduce alligatorweed
in waterways. Few other biological control agents show such dramatic
results as this beetle. Later in the 1960's, the first releases
of biological control agents management of water hyacinth resulted
in establishment. Since that time additional insects have been released
to manage hydrilla, and water lettuce. The introduction of grass
carp into Texas waters first took place in Lake Conroe in 1981.
This event and subsequent use of grass carp for biological control
of aquatic weeds is probably the most visible example of biological
control of weeds from a public standpoint.
Much of the basic research for biological control of aquatic weeds
in the United States is conducted by the Waterways
Experiment Station, Army Corps of Engineers, Vicksburg, Mississippi
and the Center for Aquatic Plants,
University of Florida. The Texas
Parks and Wildlife Department, Texas
Department of Agriculture and various other state agencies have
all contributed or helped expedite biological control of weed programs
in the state.
Programs for biological control of rangeland weeds in Texas centers
around only a few weeds, namely; puncturevine, musk thistle, field
bindweed, and salt cedar. Puncturevine weevils have contributed
to the reduction of puncturevine particularly in west Texas for
many years. Musk thistle has been studied in many other states and
became a rather recent problem in Texas. The first releases of biological
control agents against musk thistle were make in 1987 at Kerrville.
Since that time redistribution efforts have established the thistle
head weevil in several other counties in Texas. Recent work by Jerry
Michels, Texas A&M University, has focused on the use of mites
to control field bindweed. Biological control of salt cedar has
been under investigation for about ten years. Permits to study caged
leaf beetles outside of a quarantine facility in Texas were allowed
for the first time in 1999.
Biological control of weeds in Texas has clearly been lead by Jack
DeLoach, USDA-ARS at Temple. Dr. DeLoach
has been the leader on the salt cedar project. Foreign exploration
and research by Jack has contributed to both rangeland weeds and
several aquatic weeds. Jack has also contributed studies on prickly
pear and mesquite, both of which were not selected for active biological
control programs in Texas because of alternate uses of these plants.
Paul Boldt, now retired from the Temple station, was the early investigator
who studied the insects for biological control of musk thistle and
its relatives in the Mediterranean region before they were released
in the United States.
Another Angle
Another important role Texas has played is that of providing biological
control agents to manage weeds in other parts of the world and research
to support such programs. For example, prickly pear cactus had become
a problem weed in the 1920's after it was imported into Australia.
Biological control of prickly pear was an option for management
that was relatively low cost and had the potential for a permanent
solution. Consequently, Australians came to Texas and New Mexico
to investigate the insect fauna of prickly pear. A considerable
research program was conducted investigating the local insects.
This project eventually lead to the importation of the Cactoblastis
moth from South America into Australia. Caterpillars of the moth
feed on the cactus pads and the damaged pads are susceptible to
diseases that can also contribute to the demise of the plant. Since
this moth became established in Australia, prickly pear infestations
have been dramatically reduced which resulted in a major success
for biological control.
A Final Note
The western states in particular have biological control programs
for many weeds that are not known to occur in Texas or are not considered
pests here. Examples of such weeds, include leafy spurge, klamath
weed, purple loosestrife, yellow star thistle, and dalmation toadflax.
Texas remains fortunate to have avoided infestations of these weeds.
Dr.
John A. Jackman, Professor and Extension Entomology Specialist
