| Biology
Musk thistles are annuals, winter annuals, or biennials.
In Texas, seeds produced in summer germinate to form young
rosettes in the fall. The rosettes overwinter and resume
development in the spring. Stems elongate from March to
April and the plant typically flowers in April and May.
Determinate blooming continues through June, with seeds
dropping in June and July. A wide range of growth habits,
plant heights, and plant densities are possible primarily
in response to local moisture levels.
History
Musk thistle was introduced from Eurasia in about 1853,
and is now found in more than 40 states. It was first reported
in Texas by Cory (1940). Musk thistle has become a problem
weed in several counties in the Texas Hill country. It also
occurs locally in the Panhandle, Central Texas, and North
Texas.
Status
Musk thistle is a noxious weed in pastures, rangeland,
cropland, along highways, and even in many urban areas of
the U.S. This thistle is successful for many reasons such
as: it produces a large number of seeds, the seeds have
a long life, the plant competes well with other plants and
there are few natural enemies in this country. Consequently,
it continues to thrive and expand its range in Texas.
Management
Musk thistle can be controlled mechanically, chemically
with herbicides, and biologically using natural enemies
that feed on the plant. Mechanical methods consisting mainly
of mowing and hoeing are expensive. Musk thistle has long
been controlled effectively with herbicides. However, chemical
control is not usually permanent and is also expensive when
repeated every year.
The advantages of biological control program are:
- It is inexpensive
- It poses little threat to non-target organisms
- Once established, natural enemies move into adjoining
infested areas
- Little additional effort is required once a natural
enemy is established, while other controls must be applied
periodically
- It does not threaten water quality, even along streams.
Biological Control Agents
Literature
Boldt, P. E., and J. A. Jackman. 1993. Establishment of
Rhinocyllus conicus Froelich on Carduus macrocephalus
in Texas. Southwestern Entomologist 18(3): 173-181.
Cory, V. L. 1940. Six thistles recently introduced into
Texas. Madrono 5: 200-201.
Jackman, J. A., P. Boldt, J. W. Stewart and T. W. Fuchs.
1992. Biological Control of Musk Thistle in Texas. L-5067.
Biological Pest Control. Texas Agricultural Extension Service.
Texas A&M University System, College Station, TX.
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